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Horse — Care & Reference Manual

LLM-refined manual (v2 pipeline, kimi, 2026-08-04; docs/MANUAL_V2_DESIGN.md). This manual assembles the verified fact blocks in Pet Data Station that mention horse, organised along a pet owner's journey. Every quoted fact is reproduced verbatim from its cited first-hand source ([n] superscripts; see References, each tagged with a computed trust grade per docs/topic_grading_guide.md) and is independently checkable. Guide sections (checklists, red-flag box) are orientation prose in which every factual sentence carries its own [n]; derived-summary blocks from non-Open-Access sources keep their Paraphrased derived summary mark. Mis-sectioned, duplicate, off-topic and image-residue fragments were removed by the v2 builder (build-gate enforced).

Contents

1. Species Profile
2. Life-Stage Care
3. Is this pet right for you?
4. Daily & Weekly Care Checklist
5. Nutrition
6. Husbandry
7. Behavior & Training
8. Enrichment & Exercise
9. When to call a vet NOW
10. Health & Disease
11. Toxicology & Hazards
12. Grooming
13. Breeding & Neutering
14. Regulations & Legality
15. Breed-Specific Health
16. Species-Specific Health
17. Appendix A — Commercial Food & Regulatory Notes
18. Appendix B — Research Evidence

Species Profile

The profile below records this species' taxonomy, natural origin and lifespan as documented in the cited reference.

Horse (Equus caballus) and other equines — ownership profile: legal duty of care, herd-animal nature, lifetime commitment (UK DEFRA code)

Owning and caring for a horse can be a source of great enjoyment but it is also a big responsibility with a long-term caring and financial commitment. [1]

Under the Act animal owners and keepers are under a legal duty of care for the animals for which they are responsible on a permanent or temporary basis. [1]

A parent or guardian of a child under 16 years old is responsible for any animal that is owned or cared for by the child. [1]

Horses are herd animals and in the wild would live in relatively stable social groups. [1]

Research suggests that only 9% of horses die of natural causes, so planning for the timely euthanasia of your horse is a key responsibility of ownership. [1]

Life-Stage Care

Young, adult and senior care for this species, drawn from first-hand care pages and veterinary references.

Horse life-stage care — foals, pregnant mares and elderly horses have special dietary and care needs; retirement and end-of-life planning (UK DEFRA code)

As horses become older their needs may become greater and they may well require increased supervision and additional veterinary care. They may develop age-related conditions, such as dental problems, and their immune systems may become less efficient. [1]

When a horse reaches the end of its active working life, or is very elderly, consideration should be given to whether the horse can be provided with a good quality of life in retirement. Owners have a responsibility to ensure that they or whoever is entrusted with the care of such a horse is fully aware of the needs of that horse. [1]

Boxes for foaling and for mares with a foal at foot will require additional space. [1]

The transport of foals should be considered carefully to safeguard the welfare of both foal and dam. [1]

Is this pet right for you?

• A decades-long commitment: owning a horse is a big responsibility with a long-term caring and financial commitment — research suggests only 9% of horses die of natural causes, so planning for timely euthanasia is part of ownership. [1]
• A legal duty of care: under the Animal Welfare Act 2006, owners and keepers are under a legal duty of care for any horse they are responsible for, on a permanent or temporary basis. [1]
• They need company: horses are herd animals that would live in relatively stable social groups in the wild, and isolating a horse from other horses can have a negative psychological impact. [1]
• They need land: as a general rule each horse requires approximately 0.5–1.0 hectares (1.25 to 2.5 acres) of suitable grazing if no supplementary feeding is provided. [1]
• They need daily time: horses at grass should be inspected at least once a day, and stabled or group-housed horses at least twice a day. [1]
• Ongoing professional costs: hooves are usually trimmed or re-shod every 4–8 weeks, teeth should be checked by a vet or BAEDT equine dental technician at least once a year, and tetanus vaccination is strongly recommended. [1]
• Children: a parent or guardian of a child under 16 years old is responsible for any animal owned or cared for by the child. [1]

Daily & Weekly Care Checklist

Every day:

• Almost constant access to forage (grass, hay, haylage) during non-exercise hours — horses are natural grazers that eat little and often. [1]
• Continuous access to a clean supply of fresh water — around 5 to 10 litres per 100 kg bodyweight per day. [1]
• Inspect horses at grass at least once a day (stabled horses at least twice), paying attention to gait, demeanour, feet, body condition and appetite. [1]
• Pick out the hooves of stabled horses when leaving the stable, and of horses in work before and after exercise. [1]
• Daily turnout for all stabled horses (apart from those on box rest for veterinary reasons) to graze and socialise with other horses. [1]
• Tethered horses: inspect no less frequently than every six hours during normal waking hours, and give daily exercise. [1]

Every week and routine:

• Monitor weight and body condition regularly to avoid welfare problems; a sudden change in appetite or weight can be a sign of ill-health. [1]
• Groom regularly so the coat is clean and free from wounds or parasites, and to detect rug, tack or harness rubbing. [1]
• Keep fields clear of dangerous objects and poisonous plants; remove ragwort — ingestion can cause fatal liver damage. [1]
• Farrier care usually every 4–8 weeks; dental inspection at least once a year; keep tetanus vaccination up to date. [1]

Nutrition

The short version: near-constant forage, fresh water always, any concentrate ration spread over at least two meals a day, and all diet changes made gradually — sudden changes can lead to gastrointestinal upsets including colic and diarrhoea. [1] The sourced details follow.

The quotes below summarise this species' dietary requirements and nutrition-related disease risks, drawn from professional veterinary references.

Horse nutrition — fibre-based forage diet, constant forage access, clean water, gradual diet changes (UK DEFRA code)

Horses are naturally grazers who eat little and often. [1]

Horses should have almost constant access to forage (e.g. grass, hay, haylage) during their non-exercise hours. [1]

It is essential that all horses have continuous access to a clean supply of fresh water. [1]

Stabled horses should have continuous access to fresh water. [1]

If a daily concentrate ration is required it should be spread over at least two meals a day. [1]

Any diet changes (increase in volume, change in feed or hay etc.) should be made gradually. [1]

The weight and condition of every horse should be monitored regularly to avoid welfare problems. [1]

around 5 to 10 litres per 100 kg bodyweight per day [1]

in a natural state they would spend 16-20 hours a day grazing and browsing for forage [1]

Therefore all ragwort should be removed and carefully disposed of from land used for grazing horses or land that will be used to produce forage for horses. [1]

Husbandry

Space, shelter and safe pasture come first: fields kept clear of dangerous objects and poisonous plants, sturdy fencing, and stables with adequate ventilation and enough room for each horse to lie down, readily rise and turn around in comfort. [1] The sourced details follow.

Housing, environment and daily-care essentials for this species.

Horse husbandry — pasture area, daily inspection, poisonous plants, tethering limits, turnout (UK DEFRA code)

As a general rule, each horse requires approximately 0.5 – 1.0 hectares (or 1.25 to 2.5 acres) of grazing of a suitable quality if no supplementary feeding is being provided. [1]

Horses at grass should be inspected at least once a day, preferably more often. [1]

Stabled or group-housed horses should be inspected at least twice a day. [1]

Tethered horses should be inspected no less frequently than every six hours during normal waking hours [1]

Behavior & Training

Socialisation, bonding, play and preventing boredom / behaviour problems.

Horse behaviour, training and companionship — herd socialisation needs, humane training, restraint limits (UK DEFRA code)

They should be able to socialise with members of their own species. Isolating a horse from other horses can have a negative psychological impact. Where this is not possible, other animals may be used to provide company; however the company of other horses is by far the better option. Horses may become distressed if separated from other horses, or from a horse with which they have formed a pair bond. [1]

Donkeys have particular socialisation needs and can become ill – potentially fatally so - if suddenly separated from a companion that they have bonded with. [1]

Horse training should be humane, effective and safe for both horse and handler. Horses do not perform unwanted behaviours intentionally to defy their handlers; usually there is an underlying reason such as pain, discomfort, fear or habit (the behaviour has been learnt because it has been rewarded, often accidentally, in some way). [1]

Any training should be appropriate to the age, experience and condition of the animal in question. If you are unsure how to best handle your horse, advice should be sought from an experienced horse professional. [1]

Any restraint method used to assist normal management or treatment of the horse should be applied by a competent person only, and for the minimum period necessary. [1]

When forming new groups care should be taken to minimise fighting and stress, particularly when horses are to be mixed together for the first time. [1]

All stabled horses, apart from those on box rest for veterinary reasons, will benefit from daily turnout in the field to allow them to graze and socialise with other horses. [1]

Enrichment & Exercise

Toys, foraging, hiding and exercise to prevent boredom.

Horse exercise and enrichment — daily exercise and turnout, preventing stable stereotypies, stallion stimulation (UK DEFRA code)

In the wild, horses would travel long distances whilst searching for resources. Horses require adequate exercise, or freedom to exercise and this will require time and effort from the horse owner or keeper. [1]

This may have the added benefit of reducing the risk of developing abnormal behaviours such as windsucking, weaving, crib-biting, box walking and wood chewing. If turnout is not feasible, stabled horses should receive appropriate exercise daily, unless contrary to veterinary advice. Tethered horses also require daily exercise. [1]

It is important that stallions receive adequate exercise and environmental stimulation. [1]

When to call a vet NOW

• Signs of pain or colic: facial tension, reluctance to move, pawing at the ground, rolling, increased rate of respiration and sweating — contact your veterinary practice. [1]
• Sudden change in appetite or weight — this can be a sign of ill-health; your vet should be consulted if you have any concerns. [1]
• Donkeys not eating: in donkeys, loss of appetite can be life threatening in a very short period of time, so veterinary advice should be sought immediately. [1]
• Illness or pain where the cause is not clear, or first aid is not working — obtain veterinary advice promptly. [1]
• Foot problems — obtain advice from a registered farrier or vet. [1]

Preparation beats emergencies: keep your vet's contact details easily available including out-of-hours information, and keep the horse passport accessible — it is required by law, and without it some treatments may not be available. [1]

Health & Disease

Common conditions and their clinical signs, drawn from professional veterinary references. If you notice worrying signs, contact a species-experienced veterinarian promptly.

Horse emergency & illness signs — pain/colic signals, when to call the vet (UK DEFRA code)

any signs of pain or discomfort, including facial tension, reluctance to move, pawing at the ground, rolling, increased rate of respiration and sweating [1]

Veterinary advice should be obtained if the horse appears to be ill or in pain and the cause is not clear or if initial first aid treatment is not effective. [1]

If you think that there is anything wrong with your horse, contact your veterinary practice. [1]

Sudden changes can lead to gastrointestinal upsets including colic and diarrhoea and should be avoided. [1]

in donkeys, loss of appetite can be life threatening in a very short period of time so veterinary advice should be sought immediately [1]

Everyone responsible for the supervision of horses should be able to recognise signs of ill health and have a basic knowledge of equine first aid. [1]

Horse routine health care — tetanus vaccination, annual dental checks, farrier hoof care every 4-8 weeks, worm control (UK DEFRA code)

It is strongly recommended that all horses are vaccinated against tetanus as horses are very susceptible to this fatal condition. [1]

Teeth should be inspected by a vet or British Association of Equine Dental Technicians (BAEDT) equine dental technician at least once a year, and rasped or otherwise treated if necessary. [1]

Hooves should be trimmed and/or re-shod as advised by the farrier, which should usually be every 4-8 weeks. [1]

The routine use of wormers without faecal egg counts is strongly discouraged, as this will encourage parasite resistance to these drugs [1]

When a new horse enters premises, the horse should be isolated before being introduced to the rest of the herd. [1]

Become familiar with what is normal for your horse such as normal temperature, breathing rate, water consumption and mobility. [1]

Toxicology & Hazards

Substances and environmental hazards to avoid.

Horse poisonous plants and feeding hazards — ragwort, privet, yew, laburnum, sycamore seeds, oak acorns, grass cuttings (UK DEFRA code)

Some plants and trees (e.g. including privet, yew and laburnum) are also extremely toxic to horses, therefore horses should not have access to these (or their clippings) at any time. [1]

Grass cuttings are not suitable for horses to eat and care should be taken that horses do not gain access to these (i.e. garden waste or cut fields). [1]

Owners and keepers should ensure that they make themselves aware of which plants are poisonous to horses and take steps to prevent their animals ingesting these. [1]

Some plants pose a particular risk in certain seasons (e.g. sycamore tree seeds and oak trees which are most dangerous in the autumn when they shed their acorns) so arrangements should be made to mitigate such seasonal risks. [1]

Horses will eat living or cut ragwort. [1]

Gloves should be worn when removing ragwort, and it is important to remember that flowering ragwort can still seed even when removed from the ground and it has a 70% germination rate. [1]

Ragwort should be disposed of by incineration, controlled burning or landfill according to The Guidance on the Disposal Options for Common Ragwort, produced to supplement the Code of Practice and provide more detailed advice on disposal. [1]

Common Ragwort is one of the plants covered under the Weeds Act 1959, Ragwort Control Act 2003 and the Code of Practice on How to Prevent and Control the Spread of Ragwort 2006. [1]

Fields should be kept clear of dangerous objects and poisonous plants. [1]

Ragwort is toxic to horses and ingestion can result in fatal liver damage. [1]

Grooming

Brushing / bathing, nails, coat / skin and dental care.

Horse grooming and hoof care — regular grooming, daily hoof picking, rug maintenance (UK DEFRA code)

Horses should be groomed regularly to ensure that the coat is clean, free from wounds or parasites and to detect rug, tack or harness rubbing. The frequency required will depend on your horse’s management regime and coat type. [1]

Hooves of horses that are primarily field kept should be picked out and at the same time examined for signs of discomfort, wounds, injury, loose shoes, impacted foreign material, early signs of disease or anything else unusual. [1]

Stabled horses should have their feet picked out when leaving the stable and horses in work should have their feet picked out before and after exercise. [1]

Rugs should be cleaned and repaired as necessary and all fastenings kept in good working order. [1]

Breeding & Neutering

Neutering / spaying, reproduction and preventing unwanted litters.

Horse breeding considerations — suitability, heritable-condition screening of the stallion, mare/foal care costs, UK overpopulation (UK DEFRA code)

If you decide to breed from your horse, there are a number of considerations to be taken into account. You should always consider whether your horse is a suitable candidate for breeding, whether the stallion you intend to use has been inspected and is free from heritable conditions and whether you could buy or rehome a youngster rather than breeding a foal. [1]

In addition, mares have special requirements during pregnancy, foaling and the post-foaling period and you should make sure you are aware of these before breeding from your mare. The care of a young foal can be expensive and requires a large investment of time, and there is no guarantee that the foal will mature into the animal that you want. [1]

At the time of publication of this code, overpopulation of horses is a problem in the UK, and the foal’s individual future should be realistically taken into account. [1]

These may include uncastrated males (colts, stallions) and “rigs” (a stallion with undescended testicles or a horse which has been incompletely castrated). [1]

Stallions and colts can live with mixed herds but this may lead to unwanted breeding and is not recommended. [1]

A horse’s nutritional requirements will vary through its life and foals, pregnant mares and elderly horses in particular have special dietary requirements. [1]

Regulations & Legality

Legality crosswalk lines for this species, where available. Jurisdiction-specific pet law is frequently a gap — see the roadmap.

Horse — UK legal framework: Animal Welfare Act 2006 duty of care, Horse Passport (England) Regulations 2004/2009, microchipping (UK DEFRA code)

It is your responsibility to fully understand your horse’s welfare needs and what the law requires you to do to meet those needs. Breach of a provision of the Code is not an offence in itself, but if proceedings are brought against you for a welfare offence the Court will look at whether or not you have complied with the Code in deciding whether you have committed an offence. [1]

Since 2004 it has been a legal requirement (the Horse Passport (England) Regulations 2004) for all horses and ponies (and other forms of equidae) in England to have a valid passport identifying the animal and the current registered owner. [1]

These regulations were updated in 2009, requiring all foals born after the 1st July 2009 and older horses not previously identified to be microchipped when a passport is applied for. For foals, all applications must be submitted by the end of the year of their birth or within six months of birth, whichever is later. [1]

The passport must accompany the horse during all movements with a few exceptions, most notably when moved on foot or in an emergency situation, but must be produced without undue delay by the keeper if required. [1]

One of the purposes of horse passports is to record when a horse receives certain medications which may have negative consequences for human health if your animal enters the food chain at the end of its life. It is therefore essential that the passport is available whenever your vet treats your horse so he/she can record if any of these medicines are given. [1]

Horse passports should be easily accessible, as required in law, otherwise some treatments may not be available. [1]

Breed-Specific Health

Aegidienberger, Germany (Horse) — Neuronal ceroid lipofuscinosis (hereditary; OMIA-verified breed predisposition)

Breed: Aegidienberger, Germany (Horse) [2]

Disorder: Neuronal ceroid lipofuscinosis [2]

Summary: There is only 1 report of NCL in equines to date, with 3 distantly related horses of an Austrian stud in cross-breds of Icelandic horse and Peruvian paso (Url et al 2001). All three horses showed developmental retardation, slow movements and loss of appetite at the age of six months; followed by an onset of neurological symptoms that steadily progressed from the age of 1 year. The horses condition deteriorated, and was euthanized 1½ years after clinical onset. Macroscopic examination of the brain revealed slight flattening of the gyri in all 3 horses, with yellow-brownish discoloration observed in the brain of 2 horses (Url et al 2001). Microscopically, all 3 horses showed massive loss of neurons of all cortical layers of the cerebrum and a striking astrocytosis. An eosinophilic autofluorescence storage material was found mainly in neurons in the cerebral cortex and with less frequency in neurons of other brain regions, spinal cord, retina and submucous and myenteric ganglia. The storage material stained deep blue with Luxol-fast blue, (LFB) Nile blue A (NBA) and to a lesser degree, pink with periodic acid-Schiff (PAS) and black with Sudan black (SB). Immunohistochemistry (IHC) revealed large amounts of subunit c of mitochondrial ATP synthase (SCMAS) and small amounts of saponins (SAPs) storage bodies. Electron microscopy (EM) of the tissue samples revealed markedly enlarged lysosomes containing material arranged in fingerprint, curvilinear and rectilinear ultrastructural patterns. NCL in horses is suggested to be autosomal recessively inherited (Url et al 2001). [2]

Clin feat: All three horses showed developmental retardation, slow movements and loss of appetite at the age of six months (Url et al. 2001). This was followed by an onset of neurological symptoms at the age of 1 year; with characteristics of torticollis, ataxia, head tilt and visual failure (observed in 1 horse). The neurological disorders progressed, and the horses condition deteriorated. Affected horses have a reduced lifespan. [2]

Pathology: Macroscopic examination of the brain revealed slight flattening of the gyri in all 3 horses, with yellow-brownish discoloration observed in the brain of 2 horses (Url et al 2001). No atrophy of retinal layers was observed. Microscopically, all 3 horses showed massive loss of neurons of all cortical layers of the cerebrum and a striking astrocytosis. An eosinophilic, autofluorescence storage material was found mainly in neurons in the cerebral cortex and with less frequency in neurons of other brain regions, spinal cord, retina and submucous and myenteric ganglia. The storage material stained deep blue with Luxol-fast blue, (LFB) Nile blue A (NBA) and to a lesser degree, pink with periodic acid-Schiff (PAS) and black with Sudan black (SB). Immunohistochemistry (IHC) using antiserum against subunit c of mitochondrial ATP synthase (SCMAS) revealed strong, granular immunostaining in neurons of brain and spinal cord of all horses, with some present in retinal neurons of 1 horse. IHC also revealed small amounts of saponins (SAPs) storage bodies. IHC results were positive for extraneural SCMAS and both neuronal and extraneural SAPs in tissues of control horses, but that is presumably due to certain equine tissues that physiologically contain a relatively high level of SCMAS and SAPs. Electron microscopy (EM) of the tissues sample revealed markedly enlarged neuronal lysosomes containing material arranged in fingerprint and rectilinear ultrastructural patterns. Storage material was also found in lysosomes of kidney tubular cells, and in lymphocytes and macrophages of lymph nodes; with the lamellar profiles for lymph nodes storage bodies revealing rectilinear and curvilinear formations (Url et al 2001). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA entry symbol: NCL (no structured Phene_Gene link) Evidence (references) - 2001. Equine neuronal ceroid lipofuscinosis. Acta Neuropathologica — PubMed:PMID11355313 — OMIA Phene_Article / Article - 2013. Use of model organisms for the study of neuronal ceroid lipofuscinosis. Biochim Biophys Acta — PubMed:PMID23338040 | DOI:10.1016/j.bbadis.2013.01.009 — OMIA Phene_Article / Article [2]

Akhal-Teke (Horse) — Naked foal syndrome (hereditary; OMIA-verified breed predisposition)

Breed: Akhal-Teke (Horse) [3]

Mode of inheritance: Autosomal recessive [3]

Clin feat: Bauer et al. (2017): Affected horses had almost no hair and showed a mild ichthyosis. So far, all known NFS affected horses died between a few weeks and 3 years of age. It is not clear whether a specific pathology caused the premature deaths. Bauer et al. (2017) noted similarities to ST14 defects in other species: “Taken together, the ST14 gene has essential roles in the interfollicular epidermis by contributing to epidermal barrier formation as well as for hair follicle development. The observed phenotype in NFS-affected horses resembles the group of heterogeneous phenotypes caused by ST14 variants in humans and mice. However, in horses with NFS, the degree of alopecia is more severe than in human patients, whereas the ichthyosis is less pronounced, and suggested mainly by the clinical picture.” (FN thanks Emily Rogers, who provided all but the first sentence of this entry, working under the supervision of Professor Ernie Bailey; 24 April 2020) [3]

Prevalence: The variant c.388GT was homozygous in 5 affected horses and heterozygous in 10 obligate carriers. Testing of 191 other Akhal-Teke horses identified 165 homozygous for the reference sequence and 26 heterozygous for c.388GT. This variant was not found among 400 horses of other breeds. (Bauer et al., 2017) (FN thanks Emily Rogers, who provided this contribution, working under the supervision of Professor Ernie Bailey; 24 April 2020) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388959675 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Bauer et al. (2017): "Whole genome sequencing of two affected horses, two obligate carriers, and 75 control horses from other breeds revealed a single non-synonymous genetic variant on the chromosome 7 segment that was perfectly associated with NFS. The affected horses were homozygous for ST14:c.388G>T, a nonsense variant that truncates more than 80% of the open reading frame of the ST14 gene (p.G… Evidence (references) - 2011. Myosin heavy chain pattern in the Akhal-Teke horses. Animal — PubMed:PMID22439988 | DOI:10.1017/S1751731110002375 — OMIA Phene_Article / Article - 2006. The Stavropol Sphynx. Akhal-Teke Inform. — OMIA Phene_Article / Article - 2007. Again about sphynxes. Akhal-Teke Inform. — OMIA Phene_Article / Article - 2017. A nonsense variant in the ST14 gene in Akhal-Teke horses with naked foal syndrome. G3 (Bethesda) — PubMed:PMID28235824 | DOI:10.1534/g3.117.039511 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:602400 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:606797 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [3]

American Miniature Horse (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: American Miniature Horse (Horse) [4]

Mode of inheritance: Autosomal incomplete dominant [4]

Summary: As summarised by Bellone et al. (2013): Leopard complex spotting is a group of white spotting patterns in horses caused by an incompletely dominant gene (LP)... homozygotes (LP/LP) are also affected with congenital stationary night blindness. Thus, a single mutation is autosomal incompletely dominant for Leopard Complex/Appaloosa and autosomal recessive for stationary congenital night blindness ([OMIA:001341-9796]). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4161661 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Bellone et al. (2013) reported that a retroviral insertion in TRMP1 was complete associated with Leopard spotting in 511 horses from a range of breeds. Evidence (references) - 1990. The Inheritance of the Leopard Complex of Spotting Patterns in Horses. J Hered — PubMed:PMID2177073 | DOI:10.1093/oxfordjournals.jhered.a110997 — OMIA Phene_Article / Article - 2004. Assignment of the appaloosa coat colour gene (LP) to equine chromosome 1. Anim Genet — PubMed:PMID15025575 | DOI:10.1111/j.1365-2052.2004.01113.x — OMIA Phene_Article / Article - 2007. Clinical and electroretinographic characteristics of congenital stationary night blindness in the Appaloosa and the association with the leopard complex. Vet Ophthalmol — PubMed:PMID17970998 | DOI:10.1111/j.1463-5224.2007.00572.x — OMIA Phene_Article / Article - 2010. Fine-mapping and mutation analysis of TRPM1: a candidate gene for leopard complex (LP) spotting and congenital stationary night blindness in horses. Brief Funct Genomic Proteomic — PubMed:PMID20353955 | DOI:10.1093/bfgp/elq002 — OMIA Phene_Article / Article - 2012. Congenital stationary night blindness is associated with the leopard complex in the Miniature Horse. Vet Ophthalmol — PubMed:PMID22051042 | DOI:10.1111/j.1463-5224.2011.00903.x — OMIA Phene_Article / Article - 2013. Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse. PLoS One — PubMed:PMID24167615 | DOI:10.1371/journal.pone.0078280 — OMIA Phene_Article / Article - 2016. Variant in the RFWD3 gene associated with PATN1, a modifier of leopard complex spotting. Anim Genet — PubMed:PMID26568529 | DOI:10.1111/age.12375 — OMIA Phene_Article / Article - 2017. Phenotypic and genetic analysis of the leopard complex spotting in Noriker horses. J Hered — PubMed:PMID28453641 | DOI:10.1093/jhered/esx039 — OMIA Phene_Article / Article - 2015. Twenty-five thousand years of fluctuating selection on leopard complex spotting and congenital night blindness in horses. Philos Trans R Soc Lond B Biol Sci — PubMed:PMID25487337 | DOI:10.1098/rstb.2013.0386 — OMIA Phene_Article / Article - 2019. Analysis of ROH patterns in the Noriker horse breed reveals signatures of selection for coat color and body size. Anim Genet — PubMed:PMID31199540 | DOI:10.1111/age.12797 — OMIA Phene_Article / Article - 2021. Review: Balancing selection for deleterious alleles in livestock. Front Genet — PubMed:PMID34925454 | DOI:10.3389/fgene.2021.761728 — OMIA Phene_Article / Article - 2024. Spotting the pattern: A review on white coat color in the domestic horse. Animals (Basel) — PubMed:PMID38338094 | DOI:10.3390/ani14030451 — OMIA Phene_Article / Article - (2 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:613216 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:603576 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [4]

American Miniature Horse (Horse) — Silver dapple (hereditary; OMIA-verified breed predisposition)

Disorder: Silver dapple [5]

Mode of inheritance: Autosomal dominant [5]

Summary: The Silver coat color, also called Silver dapple, is characterized by dilution of the black pigment (eumelanin) in the hair. This phenotype shows an autosomal dominant inheritance. The effect of the mutation is most visible in the long hairs of the mane and tail, which are diluted to a mixture of white and gray hairs (Brunberg et al. 2006). A likely causal variant responsible for silver dilution was identified in the PMEL gene in 2006 (Brunbereg et al., 2006; Reissmann et al., 2007). See also: [OMIA:000733-9796] Multiple Congenital Ocular Anomalies (MCOA) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: PMEL17 (Entrez Gene ID 4143454) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Brunberg et al. (2006) reported that "a missense mutation in exon 11 [of PMEL17] changing the second amino acid in the cytoplasmic region from arginine to cysteine (Arg618Cys) . . . showed complete association with the Silver phenotype across multiple horse breeds [Icelandic horse; American miniature; Rocky mountain horse; Morgan horse; Swedish warmblood, Ardenne], and was not found among non-Silv… Evidence (references) - 1953. Silver dapple, a unique colour variety among Shetland ponies. Journal of Heredity — OMIA Phene_Article / Article - 2006. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genetics — PubMed:PMID17029645 | DOI:10.1186/1471-2156-7-46 — OMIA Phene_Article / Article - 2009. Genetics. It's a bull's market. Science — PubMed:PMID19390037 | DOI:10.1126/science.1173880 — OMIA Phene_Article / Article - 2009. Molecular tests for coat colours in horses. J Anim Breed Genet — PubMed:PMID19912415 | DOI:10.1111/j.1439-0388.2009.00832.x — OMIA Phene_Article / Article - 2007. Two SNPs in the SILV gene are associated with silver coat colour in ponies. Anim Genet — PubMed:PMID17257181 | DOI:10.1111/j.1365-2052.2006.01553.x — OMIA Phene_Article / Article - 2010. Pleiotropic effects of pigmentation genes in horses. Anim Genet — PubMed:PMID21070283 | DOI:10.1111/j.1365-2052.2010.02116.x — OMIA Phene_Article / Article - 2010. [Molecular basis and applicability in equine color genetics]. Yi Chuan — PubMed:PMID21513164 — OMIA Phene_Article / Article - 2011. Mutations in or near the transmembrane domain alter PMEL amyloid formation from functional to pathogenic. PLoS Genet — PubMed:PMID21949659 | DOI:10.1371/journal.pgen.1002286 — OMIA Phene_Article / Article - 2013. Equine multiple congenital ocular anomalies and silver coat colour result from the pleiotropic effects of mutant PMEL. PLoS One — PubMed:PMID24086599 | DOI:10.1371/journal.pone.0075639 — OMIA Phene_Article / Article - 2016. Distribution of coat-color-associated alleles in the domestic horse population and Przewalski's horse. J Appl Genet — PubMed:PMID27194311 | DOI:10.1007/s13353-016-0352-7 — OMIA Phene_Article / Article - 2021. Multiple congenital ocular anomalies in a silver coat Missouri Fox Trotter stallion. Tierarztl Prax Ausg G Grosstiere Nutztiere — PubMed:PMID34666370 | DOI:10.1055/a-1581-4810 — OMIA Phene_Article / Article - 2012. Coat colour and sex identification in horses from Iron Age Sweden. Ann Anat — PubMed:PMID22154005 | DOI:10.1016/j.aanat.2011.11.001 — OMIA Phene_Article / Article - (1 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:155550 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [5]

American Miniature Horse (Horse) — Splashed white, macchiato (hereditary; OMIA-verified breed predisposition)

Disorder: Splashed white, macchiato [6]

Summary: Currently (in 2016), among domesticated animals the horse is the species with the highest number of known genetic variants that lead to white spotting phenotypes. Related coat colour phenotypes are caused by variants in the EDNRB, KIT, MITF, PAX3 and TPRM1 genes. Combinations of multiple variants in these gene can lead to more pronounced coat colour phenotypes. Variants in MITF can lead to a variable degree of white spotting. The splashed white phenotype in horses is most frequently due to variants in the MITF gene, but may also be caused by variants in the PAX3 gene. As described by Hauswirth et al. (2012), The “splashed white” pattern is primarily characterized by an extremely large blaze, often accompanied by extended white markings at the distal limbs and blue eyes. Some, but not all, splashed white horses are deaf. For variants in the KIT gene that result in a white spotting phenotype see [OMIA:000209-9796]: Coat colour, dominant white in Equus caballus. [6]

Clin feat: Magdesian et al. 2009 demonstrated an increased risk for deafness in horses with the splashed white and/or frame overo spotting phenotype. Horses with the SW1 allele have an increased risk for unilateral and bilateral deafness, but the exact risk is unknown. The risk for deafness and the extent of depigmentation increase, if multiple white increasing alleles occur simultaneously in the same horse (Hauswirth et al. 2012). The macchiato Franches-Montagnes horse carrying the p.Asn210Ser variant was deaf and had low sperm quality (Blatter et al. 2013). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 210327737 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Hauswirth et al. (2012) reported a non-coding regulatory 10 bp insertion into the melanocyte-specific promoter of the MITF gene (ECA16:g.20,117,302Tdelins11; "SW1"), which disrupts a PAX3 binding site. This allele is apparently several hundred years old and can be found in many different breeds segregating for the splashed white phenotype, such as e.g. American Paint Horses, Icelandic Horses, Mini… Evidence (references) - 2009. Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype. J Am Vet Med Assoc — PubMed:PMID19912043 | DOI:10.2460/javma.235.10.1204 — OMIA Phene_Article / Article - 2012. Mutations in MITF and PAX3 cause "splashed white" and other white spotting phenotypes in horses. PLoS Genet — PubMed:PMID22511888 | DOI:10.1371/journal.pgen.1002653 — OMIA Phene_Article / Article - 2013. Accumulating Mutations in Series of Haplotypes at the KIT and MITF Loci Are Major Determinants of White Markings in Franches-Montagnes Horses. PLoS One — PubMed:PMID24098679 | DOI:10.1371/journal.pone.0075071 — OMIA Phene_Article / Article - 2017. A novel MITF variant in a white American Standardbred foal. Anim Genet — PubMed:PMID27592871 | DOI:10.1111/age.12484 — OMIA Phene_Article / Article - 2013. [Clinical evaluation of the new coat colour macchiato in a male Franches-Montagnes horse]. Schweiz Arch Tierheilkd — PubMed:PMID23531944 | DOI:10.1024/0036-7281/a000451 — OMIA Phene_Article / Article - 2017. Association analysis of KIT, MITF, and PAX3 variants with white markings in Spanish horses. Anim Genet — PubMed:PMID28084638 | DOI:10.1111/age.12528 — OMIA Phene_Article / Article - 2019. Whole-genome sequencing reveals a large deletion in the MITF gene in horses with white spotted coat colour and increased risk of deafness. Anim Genet — PubMed:PMID30644113 | DOI:10.1111/age.12762 — OMIA Phene_Article / Article - 2020. A de novo MITF deletion explains a novel splashed white phenotype in an American paint horse. J Hered — PubMed:PMID32242630 | DOI:10.1093/jhered/esaa009 — OMIA Phene_Article / Article - 2022. Non-frameshift deletion on MITF is associated with a novel splashed white spotting pattern in horses (Equus caballus). Anim Genet — PubMed:PMID35672910 | DOI:10.1111/age.13225 — OMIA Phene_Article / Article - 2023. Two novel variants in MITF and PAX3 associated with splashed white phenotypes in horses. J Equine Vet Sci — PubMed:PMID37406837 | DOI:10.1016/j.jevs.2023.104875 — OMIA Phene_Article / Article - 2023. A de novo 2.3 kb structural variant in MITF explains a novel splashed white phenotype in a Thoroughbred family. Anim Genet — PubMed:PMID37697831 | DOI:10.1111/age.13352 — OMIA Phene_Article / Article - 2023. Digital phenotyping reveals phenotype diversity and epistasis among white spotting alleles in the American Paint horse. Genes (Basel) — PubMed:PMID38002953 | DOI:10.3390/genes14112011 — OMIA Phene_Article / Article - (2 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:193510 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:103500 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:156845 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [6]

American Paint (Horse) — Curly coat (hereditary; OMIA-verified breed predisposition)

Breed: American Paint (Horse) [7]

Mode of inheritance: Morgenthaler et al (2017): in North American horses, the most frequent Curly coat phenotype is described as autosomal dominant (Crd) [Sponenberg, 1990], whereas recessive forms have been reported to segregate in the Quarter Horse, Arabian, Appaloosa, Missouri Fox Trotter, Tennessee Walking Horse, Paint, Morgan and Paso Fino breeds [Sponenberg, 1990] as well as in French Percheron horses [Blakeslee et al., 1943]. [7]

Summary: Information relating to curly coat in horses due to variants in KRT25 and SP6 was previously listed here but has been moved to gene specific entries [13/02/2026] - see [OMIA:003039-9796]: Curly coat, KRT25-related in Equus caballus (domestic horse) and [OMIA:002175-9796]: Curly coat, SP6-related in Equus caballus (domestic horse). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA molecular-genetics note: For information on likely causal variants in KRT25 and SP6 which were previously listed here see OMIA:003039-9796 : Curly coat, KRT25-related in Equus caballus (domestic horse) and OMIA:002175-9796 : Curly coat, SP6-related in Equus caballus (domestic horse). Evidence (references) - 1940. Inheritance of curliness in the horse. C.R. (Doklady) Academy of Science U.R.S.S., N.S. — OMIA Phene_Article / Article - 1990. Dominant Curly Coat in Horses. Genetics Selection Evolution — OMIA Phene_Article / Article - 2016. Rare phenotypes in domestic animals: unique resources for multiple applications. Anim Genet — PubMed:PMID26662214 | DOI:10.1111/age.12393 — OMIA Phene_Article / Article - 2017. A missense variant in the coil1A domain of the keratin 25 gene is associated with the dominant curly hair coat trait (Crd) in horse. Genet Sel Evol — PubMed:PMID29141579 | DOI:10.1186/s12711-017-0359-5 — OMIA Phene_Article / Article - 1989. Myth and mystery: the curly horse in America. New York: C.S. Fund Inc. — OMIA Phene_Article / Article - 1943. Curly coat of horses. Journal of Heredity — OMIA Phene_Article / Article - 2018. An epistatic effect of KRT25 on SP6 is involved in curly coat in horses. Sci Rep — PubMed:PMID29686323 | DOI:10.1038/s41598-018-24865-3 — OMIA Phene_Article / Article - 2024. Horse allergy: Curly Horses can mediate immune tolerance. Pneumologie — PubMed:PMID37827498 | DOI:10.1055/a-2101-9533 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:608245 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [7]

American Paint (Horse) — Equine rhabdomyolysis syndrome; Polysaccharide storage myopathy; Tying-up (hereditary; OMIA-verified breed predisposition)

Disorder: Equine rhabdomyolysis syndrome; Polysaccharide storage myopathy; Tying-up [8]

Summary: Valber et al. (1996) identified a polysaccharide storage myopathy (a glycogen storage disorder) associated with exertional rhabdomyolysis in Quarter-horse related breeds. [8]

Clin feat: As summarised by McCue et al. (2008): The phenotypic expression of PSSM ranges from muscle atrophy and progressive weakness in Draft horse breeds to muscle soreness and gait abnormalities in Warmblood breeds, and acute exertional rhabdomyolysis in Quarter Horses. The severity of clinical signs in PSSM ranges from muscle cramping and stretching out... to severe muscle pain and myoglobinuria and occasionally the complete inability to rise. [8]

Pathology: Widespread presence of subsarcolemmal vacuoles and PAS-positive inclusions (Valberg et al., 1996). [8]

Prevalence: As reported by McCue et al. (2008), The His309 allele was found in either heterozygous or homozygous form in 356 horses from 15 different breeds including Quarter Horses, Paint horses, Appaloosa horses, 5 Draft horse breeds, 3 Warmblood breeds, the Morgan, Mustang, Rocky Mountain Horse breeds, as well as mixed breed horses and Warmblood horses of unspecified breed. Its frequency ranged from 0.035 to 0.350 in different breeds. The presence of this allele in so many breeds suggests ancient origins. McCue et al. (2008) estimated its mean age at 159 generations, which means that this mutation likely originated between 1200 to 1500 years ago..., prior to the separation of the modern breeds known today. McCoy et al. (2013) reported evidence that the 309His mutation underwent historical selection in the Belgian [because Under historical conditions of daily work and limited feed, excess muscle glycogen may have been advantageous], but not in the Quarter Horse. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: GSY1 (Entrez Gene ID 4157416) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Noting that the only functional comparative gene in the candidate region of HSA19 was GYS1, McCue et al. (2008) sequenced this gene in a likely homozygous affected horse and a control horse, discovering a missense mutation (c.?G>A; p.Arg309His) whose segregation in other affected and normal horses was consistent with causality. Interestingly, McCue et al. (2008) presented evidence that this is … Evidence (references) - 1993. Muscle Histopathology and Plasma Aspartate Aminotrausferase, Creatine Kinase and Myoglobin Changes with Exercise in Horses with Recurrent Exertional Rhabdomyolysis (Erratum for Vol 25, Pg 11, 1993). Equine Veterinary Journal — OMIA Phene_Article / Article - 1993. Caffeine Contractures, Twitch Characteristics and the Threshold for Ca-2+-Induced Ca-2+ Release in Skeletal Muscle from Horses with Chronic Intermittent Rhabdomyolysis. Research in Veterinary Science — PubMed:PMID8434138 — OMIA Phene_Article / Article - 1996. Familial basis of exertional rhabdomyolysis in quarter horse-related breeds. American Journal of Veterinary Research — PubMed:PMID8669756 — OMIA Phene_Article / Article - 1997. Chronic exertional rhabdomyolysis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1997. Genetic markers in standardbred trotters susceptible to the rhabdomyolysis syndrome. Equine Veterinary Journal — PubMed:PMID9104560 — OMIA Phene_Article / Article - 1997. Exertional rhabdomyolysis and polysaccharide storage myopathy in horses. Compendium on Continuing Education for the Practicing Veterinarian — OMIA Phene_Article / Article - 1998. Exertional rhabdomyolysis. Equine Practice — OMIA Phene_Article / Article - 1998. Dietary control of exertional rhabdomyolysis in horses. Journal of the American Veterinary Medical Association — OMIA Phene_Article / Article - 1998. Renal failure, laminitis, and colitis following severe rhabdomyolysis in a draft horse-cross with polysaccharide storage myopathy. Canadian Veterinary Journal - Revue Veterinaire Canadienne — OMIA Phene_Article / Article - 1998. Skeletal muscle glycolytic capacity and phosphofructokinase regulation in horses with polysaccharide storage myopathy. American Journal of Veterinary Research — PubMed:PMID9622752 — OMIA Phene_Article / Article - 1999. Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy. Equine Veterinary Journal — PubMed:PMID9952328 — OMIA Phene_Article / Article - 1999. Postanaesthetic recumbency in a Belgian filly with polysaccharide storage myopathy. Veterinary Record — PubMed:PMID10070692 — OMIA Phene_Article / Article - (92 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:611556 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [8]

American Paint (Horse) — Glycogen storage disease IV (GSD IV); glycogen storage disease (GSD); glycogen branching enzyme deficiency (GBED); amylopectinosis (hereditary; OMIA-verified breed predisposition)

Disorder: Glycogen storage disease IV (GSD IV); glycogen storage disease (GSD); glycogen branching enzyme deficiency (GBED); amylopectinosis [9]

Mode of inheritance: Autosomal [9]

Summary: A deficiency in the glycogen branching enzyme (GBE1) is responsible for the autosomal recessive disease in American Quarter Horses initially identified as GSD and later termed GBED or Glycogen Storage Disease IV (GSD IV) after a homologous condition in people. This genetic mutation leads to the inability to mobilize glycogen leading to decreased levels of glucose in the blood and ultimately organ failure leading to death (Valberg et al., 2001; Ward et al., 2004). [9]

Clin feat: Valberg et al. (2001) investigated “related Quarter Horse foals that died by 7 weeks of age …. Clinical signs varied from stillbirth, transient flexural limb deformities, seizures, and respiratory or cardiac failure to persistent recumbency. Leukopenia … as well as high serum creatine kinase …, aspartate transaminase …, and gamma glutamyl transferase … activities were present in most foals, and intermittent hypoglycemia was present in 2 foals.“ [9]

Pathology: Valberg et al. (2001): “Gross postmortem lesions were minor, except for pulmonary edema in 2 foals. Muscle, heart, or liver samples from the foals contained abnormal periodic acid Schiff's (PAS)-positive globular or crystalline intracellular inclusions …. Accumulation of an unbranched polysaccharide in tissues was suggested by a shift in the iodine absorption spectra of polysaccharide isolated from the liver and muscle of affected foals. Skeletal muscle total polysaccharide concentrations were reduced., but liver and cardiac muscle glycogen concentrations were normal. Several glycolytic enzyme activities were normal, whereas GBE activity was virtually absent in. affected foals. GBE activities in peripheral blood cells of dams of affected foals and several of their half-siblings or full siblings were approximately 50% of controls. GBE protein in liver. was markedly reduced to absent in affected foals, and in a half-sibling of an affected foal, it was approximately one-half the amount of normal controls.” Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4143712 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 2001. Glycogen branching enzyme deficiency in quarter horse foals. Journal of Veterinary Internal Medicine — PubMed:PMID11817063 — OMIA Phene_Article / Article - 2004. Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV. Mamm Genome — PubMed:PMID15366377 — OMIA Phene_Article / Article - 2003. Genetic mapping of GBE1 and its association with glycogen storage disease IV in American Quarter horses. Cytogenet Genome Res — PubMed:PMID14970703 | DOI:10.1159/000075749 — OMIA Phene_Article / Article - 2009. Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. J Am Vet Med Assoc — PubMed:PMID19119976 | DOI:10.2460/javma.234.1.120 — OMIA Phene_Article / Article - 2020. Preclinical research in glycogen storage diseases: A comprehensive review of current animal models. Int J Mol Sci — PubMed:PMID33348688 | DOI:10.3390/ijms21249621 — OMIA Phene_Article / Article - 2020. Efficient correction of a deleterious point mutation in primary horse fibroblasts with CRISPR-Cas9. Sci Rep — PubMed:PMID32366884 | DOI:10.1038/s41598-020-62723-3 — OMIA Phene_Article / Article - 1999. Amylopectinosis in fetal and neonatal Quarter Horses. Vet Pathol — PubMed:PMID10098645 | DOI:10.1354/vp.36-2-157 — OMIA Phene_Article / Article - 2003. Muscular weakness and recumbency in a Quarter Horse colt due to glycogen branching enzyme deficiency. Equine Veterinary Education — DOI:https://doi.org/10.1111/j.2042-3292.2003.tb00240.x — OMIA Phene_Article / Article - 2022. Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci — PubMed:PMID36150530 | DOI:10.1016/j.jevs.2022.104129 — OMIA Phene_Article / Article - 2023. Administration and detection of gene therapy in horses: A systematic review. Drug Test Anal — PubMed:PMID36269665 | DOI:10.1002/dta.3394 — OMIA Phene_Article / Article - 2024. Genome-wide equine preimplantation genetic testing enabled by simultaneous haplotyping and copy number detection. Sci Rep — PubMed:PMID38263320 | DOI:10.1038/s41598-023-48103-7 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - (3 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:232500 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:607839 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [9]

American Paint (Horse) — Neuroaxonal dystrophy, generic (hereditary; OMIA-verified breed predisposition)

Mode of inheritance: Multifactorial [10]

Summary: In a detailed review, Finno and Johnson (2022) stated it was apparent that eNAD [equine NeuroAxonal Dystrophy; this OMIA entry] was clinically indistinguishable from EDM [Equine Degenerative Myeloencephalopathy; [OMIA:001163-9796]: Myeloencephalopathy, degenerative in Equus caballus], and the current consensus is that the conditions have such striking clinical and pathologic similarities that eNAD could be considered a localized form of EDM or EDM a more diffuse form of eNAD. Powers et al. (2024): Equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM) is a neurodegenerative disease that primarily affects young, genetically predisposed horses that are deficient in vitamin E. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA entry symbol: eNAD (no structured Phene_Gene link) - OMIA molecular-genetics note: Transcriptome profiling by Finno et al. (2016) led them to "hypothesize that the protective role of α-TOH [α-tocopherol] in eNAD may reside in its ability to prevent oxysterol accumulation and subsequent activation of the LXR [liver X receptor] in order to decrease lipid peroxidation associated neurodegeneration." Evidence (references) - 1996. Neuroaxonal dystrophy in a two-year-old quarter horse filly. Canadian Veterinary Journal — OMIA Phene_Article / Article - 2013. Pedigree analysis and exclusion of alpha-tocopherol transfer protein (TTPA) as a candidate gene for neuroaxonal dystrophy in the American Quarter Horse. J Vet Intern Med — PubMed:PMID23186252 | DOI:10.1111/jvim.12015 — OMIA Phene_Article / Article - 2012. Electrophysiological studies in American Quarter horses with neuroaxonal dystrophy. Vet Ophthalmol — PubMed:PMID22432889 | DOI:10.1111/j.1463-5224.2012.00997.x — OMIA Phene_Article / Article - 2011. Equine degenerative myeloencephalopathy in Lusitano horses. J Vet Intern Med — PubMed:PMID22092640 | DOI:10.1111/j.1939-1676.2011.00817.x — OMIA Phene_Article / Article - 2015. Blood and cerebrospinal fluid α-tocopherol and selenium concentrations in neonatal foals with neuroaxonal dystrophy. J Vet Intern Med — PubMed:PMID26391904 | DOI:10.1111/jvim.13618 — OMIA Phene_Article / Article - 2016. Transcriptome profiling of equine vitamin E deficient neuroaxonal dystrophy identifies upregulation of liver X receptor target genes. Free Radic Biol Med — PubMed:PMID27751910 | DOI:10.1016/j.freeradbiomed.2016.10.009 — OMIA Phene_Article / Article - 2020. Genome-wide association study and subsequent exclusion of ATCAY as a candidate gene involved in equine neuroaxonal dystrophy using two animal models. Genes (Basel) — PubMed:PMID31936863 | DOI:10.3390/genes11010082 — OMIA Phene_Article / Article - 2021. Increased α-tocopherol metabolism in horses with equine neuroaxonal dystrophy. J Vet Intern Med — PubMed:PMID34331715 | DOI:10.1111/jvim.16233 — OMIA Phene_Article / Article - 2022. Equine neuroaxonal dystrophy and degenerative myeloencephalopathy. Vet Clin North Am Equine Pract — PubMed:PMID35811203 | DOI:10.1016/j.cveq.2022.04.003 — OMIA Phene_Article / Article - 2023. Cerebrospinal fluid and serum proteomic profiles accurately distinguish neuroaxonal dystrophy from cervical vertebral compressive myelopathy in horses. J Vet Intern Med — PubMed:PMID36929645 | DOI:10.1111/jvim.16660 — OMIA Phene_Article / Article - 2024. Clinical and histopathological features in horses with neuroaxonal degeneration: 100 cases (2017-2021). J Vet Intern Med — PubMed:PMID38095342 | DOI:10.1111/jvim.16969 — OMIA Phene_Article / Article - 2011. Evaluation of epidemiological, clinical, and pathological features of neuroaxonal dystrophy in Quarter Horses. J Am Vet Med Assoc — PubMed:PMID21916766 | DOI:10.2460/javma.239.6.823 — OMIA Phene_Article / Article - (10 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:608507 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [10]

American Paint (Horse) — Overo lethal white foal syndrome; frame overo spotting (hereditary; OMIA-verified breed predisposition)

Disorder: Overo lethal white foal syndrome; frame overo spotting [11]

Summary: As with white spotting, the Overo coat-colour pattern is characterised by pigment spreading down both sides from the dorsal midline, giving way to lack of pigment (i.e. white) primarily on the ventral surfaces. Unfortunately, homozygosity for the Overo allele results in white or nearly white foals which die within a few days of birth: the so-called lethal white foal sysndrome (LWFS). The cause of death is intestinal obstruction resulting from a lack of nerve cells in the distal portion of the large intestine (aganglionic megacolon), which is thought to be due to a fault in the proliferation and/or migration of nerve stem cells from the neural crest of the developing embryo. [11]

Prevalence: Badial et al. (2018) developed and validated a high-resolution melting (HRM) genotyping assay to detect the OLWFS causative mutation, and... also determined the frequency of heterozygotes among American Paint horses in Brazil.... The overall estimated frequency of heterozygotes was 21.6%; however, this frequency increased to 89.5% when considering only overo horses. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4143446 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Noting that mutations in the genes for endothelin 3 (EDN3) or its receptor (EDNRB) are responsible for similar disorders in humans and rodents, Santschi et al. (1998), from the University of Minnesota, sequenced cDNA from 22 affected foals, their parents, and some solid-colour normal controls, all registered with the American Paint Horse Association. There was no variation in the EDN3 gene, but a … Evidence (references) - 1990. Overo Lethal White Foal Syndrome - Equine Model of Aganglionic Megacolon (Hirschsprung Disease). American Journal of Medical Genetics — PubMed:PMID2363434 | DOI:10.1002/ajmg.1320360319 — OMIA Phene_Article / Article - 1987. Current research topics in equine genetics, Part 1. Equine Practice — OMIA Phene_Article / Article - 1990. Megacolon in 2 Related Clydesdale Foals. Australian Veterinary Journal — PubMed:PMID2076076 — OMIA Phene_Article / Article - 1994. Dominant inheritance of overo spotting in paint horses. Journal of Heredity — PubMed:PMID8014463 — OMIA Phene_Article / Article - 1995. Overo spotting in horses. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 1998. Endothelin receptor B mutation associated with lethal white foal syndrome in horses [abstract]. Plant & Animal Genome VI — OMIA Phene_Article / Article - 1998. Endothelin receptor B polymorphism associated with lethal white foal syndrome in horses. Mammalian Genome — PubMed:PMID9530628 — OMIA Phene_Article / Article - 1982. Ileocolonic aganglionosis in white progeny of overo spotted horses. Journal of the American Veterinary Medicine Association — OMIA Phene_Article / Article - 1998. A missense mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome - an equine version of Hirschsprung-disease. Mammalian Genome — PubMed:PMID9585428 — OMIA Phene_Article / Article - 1998. A dinucleotide mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome (LWFS) - a horse variant of Hirschsprung-disease (HSCR). Human Molecular Genetics — PubMed:PMID9580670 — OMIA Phene_Article / Article - 1983. Congenital intestinal megacolon in white foals. Veterinary Pathology — PubMed:PMID6849219 — OMIA Phene_Article / Article - 2001. Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. American Journal of Veterinary Research — PubMed:PMID11197568 — OMIA Phene_Article / Article - (22 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:600155 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:277580 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600501 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:131244 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [11]

American Paint (Horse) — Palomino (hereditary; OMIA-verified breed predisposition)

Disorder: Palomino [12]

Summary: In 2003, Mariat et al. showed that this classic coat-colour locus encodes membrane-associated transporter protein (MATP), now renamed SLC45A2, and that the first reported dilution allele in horses is due to a missense mutation [FN 16 Oct 2003]. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: MATP (Entrez Gene ID 5474234) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Building on the strong evidence from mapping (see Mapping section above), Mariat et al. (2003) identified a missense G457A transition (omia.variant:153) in the equine MATP gene (now called SLC45A2), giving rise to a D153N amino acid substitution in cream horses. Sevane et al. (2019) reported a "missense variation in exon 4 [SLC45A2:c.985G>A; SLC45A2:p.(Ala329Thr), omia.variant… Evidence (references) - 1951. New evidence on the genetics of the Palomino horse. J Hered — PubMed:PMID14832452 — OMIA Phene_Article / Article - 2001. The cream dilution gene, responsible for the palomino and buckskin coat colours, maps to horse chromosome 21. Animal Genetics — PubMed:PMID11736803 — OMIA Phene_Article / Article - 2003. A mutation in the MATP gene causes the cream coat colour in the horse. Genetics Selection Evolution — PubMed:PMID12605854 | DOI:10.1051/gse:2002039 — OMIA Phene_Article / Article - 2008. Technical note: a novel method for routine genotyping of horse coat color gene polymorphisms. J Anim Sci — PubMed:PMID18310485 | DOI:10.2527/jas.2007-0498 — OMIA Phene_Article / Article - 2009. Development of a method for simultaneously genotyping multiple horse coat colour loci and genetic investigation of basic colour variation in Thoroughbred and Misaki horses in Japan. J Anim Breed Genet — PubMed:PMID19912416 | DOI:10.1111/j.1439-0388.2009.00841.x — OMIA Phene_Article / Article - 2009. Genetics. It's a bull's market. Science — PubMed:PMID19390037 | DOI:10.1126/science.1173880 — OMIA Phene_Article / Article - 2009. Molecular tests for coat colours in horses. J Anim Breed Genet — PubMed:PMID19912415 | DOI:10.1111/j.1439-0388.2009.00832.x — OMIA Phene_Article / Article - 2010. Pleiotropic effects of pigmentation genes in horses. Anim Genet — PubMed:PMID21070283 | DOI:10.1111/j.1365-2052.2010.02116.x — OMIA Phene_Article / Article - 2010. [Molecular basis and applicability in equine color genetics]. Yi Chuan — PubMed:PMID21513164 — OMIA Phene_Article / Article - 1946. Genetics of the Palomino horse; confirmation of the Salisbury-Britton hypothesis. J Hered — PubMed:PMID21025138 | DOI:10.1093/oxfordjournals.jhered.a105569 — OMIA Phene_Article / Article - 1948. The Abc of color inheritance in horses. Genetics — PubMed:PMID17247268 | DOI:10.1093/genetics/33.1.22 — OMIA Phene_Article / Article - 1961. The palomino horse. Genetics — PubMed:PMID13877241 | DOI:10.1093/genetics/46.9.1143 — OMIA Phene_Article / Article - (10 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:606574 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:227240 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:606202 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [12]

American Paint (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Disorder: Tobiano, Sabino [13]

Prevalence: Druml et al. (2018) reported that the SB1 variant is present in three breeds (Haflinger, 14 out of 98; Noriker, four out of 189; Lipizzan one out of 329)... None of the SB1/sb1-carrier horses met the criteria defining the Sabino1 pattern according to current applied protocols. Esdaile et al. (2021): The estimated allele frequency of W13 in the American Miniature Horse was 0.0063 (79 N/N, 1 W13/N) and the allele was not detected in a random sample (n = 59) of Shetland ponies. In the same study 14 out of 19 all-white unregistered Shetland ponies were heterozygous for the W13 variant. [13]

Gen test: McFadden et al. (2024, PMID: 38338160) propose KIT variants be reported as phased genotypes or the separation of different loci to more accurately report genotypes. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: c-kit (Entrez Gene ID 5430480) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Using the comparative candidate-gene strategy (based on the KIT gene being associated with similar coat-colour-phenotypes in humans and pigs), Brooks and Bailey (2005) sequenced the KIT gene in horses of each of the three genotypes at a Sabino-spotting locus they called Sabino 1, and identified a splice variant (omia.variant:885), namely "a base substitution for T with A in intron 16, 1037 bases f… Evidence (references) - 1978. Linkage of tobiano coat spotting and albumin markers in a pony family. Journal of Heredity — PubMed:PMID569673 — OMIA Phene_Article / Article - 2002. A PCR-RFLP for KIT associated with tobiano spotting pattern in horses. Animal Genetics — PubMed:PMID12139510 — OMIA Phene_Article / Article - 2005. Exon skipping in the KIT gene causes a Sabino spotting pattern in horses. Mamm Genome — PubMed:PMID16284805 | DOI:10.1007/s00335-005-2472-y — OMIA Phene_Article / Article - 2004. Genetic mapping of dominant white (W), a homozygous lethal condition in the horse (Equus caballus). Journal of Animal Breeding and Genetics — OMIA Phene_Article / Article - 2007. A chromosome inversion near the KIT gene and the Tobiano spotting pattern in horses. Cytogenet Genome Res — PubMed:PMID18253033 | DOI:10.1159/000112065 — OMIA Phene_Article / Article - 2008. An equine chromosome 3 inversion is associated with the tobiano spotting pattern in German horse breeds. Anim Genet — PubMed:PMID18410476 | DOI:10.1111/j.1365-2052.2008.01715.x — OMIA Phene_Article / Article - 2007. Allelic heterogeneity at the equine KIT locus in dominant white (W) horses. PLoS Genet — PubMed:PMID17997609 | DOI:10.1371/journal.pgen.0030195 — OMIA Phene_Article / Article - 1969. Lethal dominant white in horses. J Hered — PubMed:PMID5816567 — OMIA Phene_Article / Article - 2008. Genetic analysis of white facial and leg markings in the Swiss Franches-Montagnes Horse Breed. J Hered — PubMed:PMID18296388 | DOI:10.1093/jhered/esm115 — OMIA Phene_Article / Article - 2009. Seven novel KIT mutations in horses with white coat colour phenotypes. Anim Genet — PubMed:PMID19456317 | DOI:10.1111/j.1365-2052.2009.01893.x — OMIA Phene_Article / Article - 2009. Haematological parameters are normal in dominant white Franches-Montagnes horses carrying a KIT mutation. Vet J — PubMed:PMID19362501 | DOI:10.1016/j.tvjl.2009.02.017 — OMIA Phene_Article / Article - 2010. An unexpected advantage of whiteness in horses: the most horsefly-proof horse has a depolarizing white coat. Proc Biol Sci — PubMed:PMID20129982 | DOI:10.1098/rspb.2009.2202 — OMIA Phene_Article / Article - (38 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:172800 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:164920 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [13]

American Paint (Horse) — splashed white (hereditary; OMIA-verified breed predisposition)

Disorder: splashed white [14]

Summary: Currently (in 2016), the horse is among domesticated animals the species with the highest number of known genetic variants that lead to white spotting phenotypes. Related coat colour phenotypes are caused by variants in the EDNRB, KIT, MITF, PAX3 and TRPM1 genes. Combinations of multiple variants in these gene can lead to more pronounced coat colour phenotypes. The splashed white phenotype may be caused by variants in the PAX3 gene as outlined below. However, by far the most common causative varaint for the splashed white phenotype is a non-coding regulatory promoter variant in the MITF gene. [14]

Prevalence: Druml et al. (2018) reported that besides Quarter Horses, the PAX3^C70Y [SW2] allele is also present in Noriker (seven out of 189) and Lipizzan (three out of 329) horses and that of 10 heterozygous PAX3^C70Y-carrier horses, two had nearly a splashed white phenotype. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 210342596 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Hauswirth et al. (2012) reported three independent variants causing the splashed white phenotype, two of them in the MITF gene and one in the PAX3 gene: A missense variant in the PAX3 gene [omia.variant:791] (c.209G>A; p.C70Y; "SW2") was identified in Quarter Horses and American Paint Horses. Druml et al. (2018) demonstrated that the PAX3^C70Y allele also segregates in Noriker and Lippizan hors… Evidence (references) - 2009. Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype. J Am Vet Med Assoc — PubMed:PMID19912043 | DOI:10.2460/javma.235.10.1204 — OMIA Phene_Article / Article - 2012. Mutations in MITF and PAX3 cause "splashed white" and other white spotting phenotypes in horses. PLoS Genet — PubMed:PMID22511888 | DOI:10.1371/journal.pgen.1002653 — OMIA Phene_Article / Article - 2013. Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes. Anim Genet — PubMed:PMID23659293 | DOI:10.1111/age.12057 — OMIA Phene_Article / Article - 2017. A novel MITF variant in a white American Standardbred foal. Anim Genet — PubMed:PMID27592871 | DOI:10.1111/age.12484 — OMIA Phene_Article / Article - 2017. Association analysis of KIT, MITF, and PAX3 variants with white markings in Spanish horses. Anim Genet — PubMed:PMID28084638 | DOI:10.1111/age.12528 — OMIA Phene_Article / Article - 2018. Novel insights into Sabino1 and splashed white coat color patterns in horses. Anim Genet — PubMed:PMID29635692 | DOI:10.1111/age.12657 — OMIA Phene_Article / Article - 2019. Correction: Mutations in MITF and PAX3 cause "Splashed White" and other white spotting phenotypes in horses. PLoS Genet — PubMed:PMID31374075 | DOI:10.1371/journal.pgen.1008321 — OMIA Phene_Article / Article - 2023. Two novel variants in MITF and PAX3 associated with splashed white phenotypes in horses. J Equine Vet Sci — PubMed:PMID37406837 | DOI:10.1016/j.jevs.2023.104875 — OMIA Phene_Article / Article - 2023. Digital phenotyping reveals phenotype diversity and epistasis among white spotting alleles in the American Paint horse. Genes (Basel) — PubMed:PMID38002953 | DOI:10.3390/genes14112011 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Spotting the pattern: A review on white coat color in the domestic horse. Animals (Basel) — PubMed:PMID38338094 | DOI:10.3390/ani14030451 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:193500 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:148820 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:606597 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [14]

American Saddle Horse (Horse) — Also known as Epitheliogenesis imperfecta. (hereditary; OMIA-verified breed predisposition)

Breed: American Saddle Horse (Horse) [15]

Disorder: Also known as Epitheliogenesis imperfecta. [15]

Prevalence: Graves et al. (2009) reported that nine of 175 randomly selected American Saddlebred foals from the 2007 foal crop were found to be carriers of the [deletion] mutation (frequency of 0.026). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 112445582 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: By sequence analysis of three strong comparative candidate genes, Graves et al. (2009) identified a causal mutation as a "6589-bp deletion spanning exons 24-27 . . . in the LAMA3 gene in American Saddlebred foals" [omia.variant:658]. Evidence (references) - 1976. Epitheliogenesis imperfecta in a foal. J Am Vet Med Assoc — PubMed:PMID1245446 — OMIA Phene_Article / Article - 2002. Equine epitheliogenesis imperfecta in two American Saddlebred foals is a lamina lucida defect. Vet Pathol — PubMed:PMID12243468 | DOI:10.1354/vp.39-5-576 — OMIA Phene_Article / Article - 2003. The epitheliogenesis imperfecta locus maps to equine chromosome 8 in American Saddlebred horses. Cytogenet Genome Res — PubMed:PMID14970704 | DOI:10.1159/000075750 — OMIA Phene_Article / Article - 2009. Partial deletion of the LAMA3 gene is responsible for hereditary junctional epidermolysis bullosa in the American Saddlebred Horse. Anim Genet — PubMed:PMID19016681 | DOI:10.1111/j.1365-2052.2008.01795.x — OMIA Phene_Article / Article - 2005. cDNA sequence of the horse (Equus caballus) LAMA3 gene and characterization of two intronic SNP markers. DNA Seq — PubMed:PMID16287627 | DOI:10.1080/10425170500287674 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:226700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600805 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:245660 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:226650 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [15]

American Saddle Horse (Horse) — Night blindness, congenital stationary, GRM6-related (hereditary; OMIA-verified breed predisposition)

Summary: Hack et al. (2021) reported a Tennessee Walking Horse with congenital stationary night blindness (CSNB) that did not have a the TRPM1 variant known to cause CSNB in horses (see OMIA:001341-9796: Night blindness, congenital stationary, TRPM1-related in Equus caballus). Esdaile et al. (2024) provides additional evidence that GRM6 c.533C>T homozygosity is likely causal to CSNB in Tennessee Walking Horses, Standardbreds, and Missouri Fox Trotting Horses. [16]

Prevalence: Hack et al. (2021): This variant [GRM6 c.533C>T] was not detected in 273 horses from three additional breeds. The estimated allele frequency in Tennessee Walking Horses is 10%. Esdaile et al. (2024): The CSNB2 allele was present in nine breeds [American Quarter Horse, Racking Horse, Rocky Mountain Horse, American Saddlebred, Spotted Saddle Horse, Standardbred (pacer), Miniature Horse, Missouri Fox Trotting Horse, Morgan], ranging in frequency from 0.0010 in American Quarter Horses (n = 486) to 0.17 in pacing Standardbreds (n = 110.). The CSNB2 allele was not detected in trotting Standardbreds (n = 70), Thoroughbreds (n = 1787), Hackney Horses (n = 47), Hackney Ponies (n = 44), and Shetland Ponies (n = 99.). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388955788 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Hack et al. (2021): "WGS [whole genome sequencing] analysis identified a missense mutation in metabotropic glutamate receptor 6 (GRM6) (c.533C>T p.Thr178Met)." Evidence (references) - 2021. Whole-genome sequencing identifies missense mutation in GRM6 as the likely cause of congenital stationary night blindness in a Tennessee Walking Horse. Equine Vet J — PubMed:PMID32654228 | DOI:10.1111/evj.13318 — OMIA Phene_Article / Article - 2024. Additional evidence supports GRM6 p.Thr178Met as a cause of congenital stationary night blindness in three horse breeds. Vet Ophthalmol — PubMed:PMID37815029 | DOI:10.1111/vop.13151 — OMIA Phene_Article / Article - 2024. Consensus guidelines for nomenclature of companion animal inherited retinal disorders. Vet Ophthalmol — PubMed:PMID38334230 | DOI:10.1111/vop.13185 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:604096 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:257270 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [16]

American Trotter (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: American Trotter (Horse) [17]

Disorder: Chestnut [17]

Summary: Various theories on the inheritance of horse coat colours have existed for many decades. Since the 1990s, the full force of molecular biology has been brought to bear on this topic. The first results of such work in horses were reported by Marklund et al. (1996) (see below). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: MSH-R (Entrez Gene ID 4211893) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: By cloning and sequencing a very likely comparative candidate gene (based on the very reasonable assumption that chestnut coat colour in horses is due to an allele at the extension locus), Marklund et al. (1996) showed that chestnut coat colour in 12 different breeds is due to a missense mutation in the gene for melanocyte-stimulating hormone receptor (MSHR or MC1R). Evidence (references) - 1982. A linkage group composed of 3 coat colour genes and 3 serum protein loci in horses. Journal of Heredity — PubMed:PMID7096983 — OMIA Phene_Article / Article - 1994. Parentage Testing and Linkage Analysis in the Horse Using a Set of Highly Polymorphic Microsatellites. Animal Genetics — PubMed:PMID8161016 — OMIA Phene_Article / Article - 1996. The equine MSH-R TaqI RFLP is not informative for hair colour in Arabian horses. Animal Genetics — PubMed:PMID8624048 — OMIA Phene_Article / Article - 1996. A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses. Mammalian Genome — PubMed:PMID8995760 — OMIA Phene_Article / Article - 1997. Dominant black in horses. Genetics Selection Evolution — OMIA Phene_Article / Article - 2001. Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). Mammalian Genome — PubMed:PMID11353392 | DOI:10.1007/s003350020017 — OMIA Phene_Article / Article - 2001. Analysis of the genetic structure of the breeding nucleus of the Russian population of thoroughbred horses by the extension locus molecular DNA typing. Russian Journal of Genetics — OMIA Phene_Article / Article - 2002. Horse breeding: genetic tests for the coat colors chestnut, bay and black. Results from a first study in the Swiss Franches-Montagnes horse breed. Schweiz Arch Tierheilkd — PubMed:PMID12224446 | DOI:10.1024/0036-7281.144.8.405 — OMIA Phene_Article / Article - 2003. Melanocortin receptor variants with phenotypic effects in horse, pig, and chicken. Annals of the New York Academy of Sciences — PubMed:PMID12851331 — OMIA Phene_Article / Article - 2008. Technical note: a novel method for routine genotyping of horse coat color gene polymorphisms. J Anim Sci — PubMed:PMID18310485 | DOI:10.2527/jas.2007-0498 — OMIA Phene_Article / Article - 2009. Identification of horse chestnut coat color genotype using SNaPshot. BMC Res Notes — PubMed:PMID20015355 | DOI:10.1186/1756-0500-2-255 — OMIA Phene_Article / Article - 2009. Development of a method for simultaneously genotyping multiple horse coat colour loci and genetic investigation of basic colour variation in Thoroughbred and Misaki horses in Japan. J Anim Breed Genet — PubMed:PMID19912416 | DOI:10.1111/j.1439-0388.2009.00841.x — OMIA Phene_Article / Article - (28 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:266300 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:155555 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [17]

American Trotter (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Summary: Dun is a wild-type coat color in horses characterized by pigment dilution with a striking pattern of dark areas termed primitive markings. (Imsland et al., 2016). Primitive markings usually appear as a dorsal stripe and bars on the legs. Primitive markings usually appear as a dorsal stripe and bars on the legs. These primitive markings were discussed at some length by Darwin (1859) (chap 5, pp. 163-167).br Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388946510 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Following mapping, the candidate region was DNA sequenced leading to the discovery of a pair of insertions associated with the D and d1 alleles. The D allele appears as an 8 bp insertion followed downstream by a 1609 bp insertion. The d1 allele, described as having no dilution but showing primitive markings, appears as an 8 bp insertion followed downstream by a 1610 bp insertion. The d2 allele is … Evidence (references) - 1859. On the Origin of Species by Means of Natural Selection. John Murray, London — OMIA Phene_Article / Article - 1978. Inheritance of yellow dun and blue dun in the Icelandic toelter horse. J Hered — PubMed:PMID731005 | DOI:10.1093/oxfordjournals.jhered.a108913 — OMIA Phene_Article / Article - 2016. Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nat Genet — PubMed:PMID26691985 | DOI:10.1038/ng.3475 — OMIA Phene_Article / Article - 2019. TBX3 and ASIP genotypes reveal discrepancies in officially recorded coat colors of Hucul horses. Animal — PubMed:PMID30614426 | DOI:10.1017/S1751731118003506 — OMIA Phene_Article / Article - 2021. Genetic background of the Polish primitive horse (Konik) coat color variation-new insight into dun dilution phenotypic effect. J Hered — PubMed:PMID34432873 | DOI:10.1093/jhered/esab034 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2023. Evaluation of genetic markers in the analysis of the colors and marks occurrence in the Vyatka breed horses. Vestnik of the Russian Agricultural Science — DOI:10.31857/2500-2082/2023/3/89-94 — OMIA Phene_Article / Article - 2017. Variation in TBX3 gene region in dun coat color Polish Konik horses. Journal of Equine Veterinary Science — DOI:10.1016/j.jevs.2016.10.003 — OMIA Phene_Article / Article - 2024. Expression and analysis of TBX3 gene in the skin from three locations on dun Mongolian Bider horse. Genes (Basel) — PubMed:PMID39766856 | DOI:10.3390/genes15121589 — OMIA Phene_Article / Article - 2026. Differential expression and analysis of TBX3 gene in skin tissues of dun mongolian horses with and without bider markings. Animals (Basel) — PubMed:PMID41594486 | DOI:10.3390/ani16020297 — OMIA Phene_Article / Article - 2026. Genetic background and phenotypic features of the endangered Miyako horse. J Equine Sci — PubMed:PMID41859759 | DOI:10.1294/jes.37.27 — OMIA Phene_Article / Article - 2026. Unraveling the molecular mechanism of Bider marking formation in dun Mongolian horses through transcriptome sequencing. Animals (Basel) — PubMed:PMID42071913 | DOI:10.3390/ani16081145 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:601621 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [18]

American Trotter (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Mode of inheritance: Sigurðardóttir et al. (2023) provided convincing evidence of the multifactorial nature of gaitedness. However, this entry focuses on variation in gaitedness due to DMRT3 variants and is therefore listed as single locus related in horses. [19]

Prevalence: Promerová et al. (2014) genotyped 4396 horses representing 141 horse breeds for the DMRT3 stop mutation. More than half (2749) of these horses also were genotyped for a SNP situated 32 kb upstream of the DMRT3 nonsense mutation because these two SNPs are in very strong linkage disequilibrium. We show that the DMRT3 mutation is present in 68 of the 141 genotyped horse breeds at a frequency ranging from 1% to 100%. We also show that the mutation is not limited to a geographical area, but is found worldwide. The breeds with a high frequency of the stop mutation (>50%) are either classified as gaited or bred for harness racing. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: DMRT3 (Entrez Gene ID 366703877) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: From a genome scan of 70 Icelandic horses (40 that can pace and 30 that can't pace), Andersson et al. (2012) identified a 684kb region of chromosome ECA23 showing a very strong association with ability to pace. Resequencing within this region eventually identified the causative mutation as a nonsense mutation (Ser301STOP) in DMRT3 (previously listed as LOC100147177 in NCBI), which encodes a transc… Evidence (references) - 2012. Mutations in DMRT3 affect locomotion in horses and spinal circuit function in mice. Nature — PubMed:PMID22932389 | DOI:10.1038/nature11399 — OMIA Phene_Article / Article - 1987. Genetic differentiation associated with gait within American standardbred horses. Anim Genet — PubMed:PMID3481678 | DOI:10.1111/j.1365-2052.1987.tb00772.x — OMIA Phene_Article / Article - 2013. Genome-wide analysis reveals selection for important traits in domestic horse breeds. PLoS Genet — PubMed:PMID23349635 | DOI:10.1371/journal.pgen.1003211 — OMIA Phene_Article / Article - 1907. Trotting and pacing: dominant and recessive?. Science — OMIA Phene_Article / Article - 2014. Worldwide frequency distribution of the 'Gait keeper' mutation in the DMRT3 gene. Anim Genet — PubMed:PMID24444049 | DOI:10.1111/age.12120 — OMIA Phene_Article / Article - 2015. The DMRT3 gene mutation in Chinese horse breeds. Anim Genet — PubMed:PMID25917306 | DOI:10.1111/age.12292 — OMIA Phene_Article / Article - 2015. DMRT3 is associated with gait type in Mangalarga Marchador horses, but does not control gait ability. Anim Genet — PubMed:PMID25690906 | DOI:10.1111/age.12273 — OMIA Phene_Article / Article - 2014. The DMRT3 'Gait keeper' mutation affects performance of Nordic and Standardbred trotters. J Anim Sci — PubMed:PMID25085403 | DOI:10.2527/jas.2014-7803 — OMIA Phene_Article / Article - 2015. Different DMRT3 Genotypes Are Best Adapted for Harness Racing and Riding in Finnhorses. J Hered — PubMed:PMID26285915 | DOI:10.1093/jhered/esv062 — OMIA Phene_Article / Article - 2016. Rare phenotypes in domestic animals: unique resources for multiple applications. Anim Genet — PubMed:PMID26662214 | DOI:10.1111/age.12393 — OMIA Phene_Article / Article - 2016. The origin of ambling horses. Curr Biol — PubMed:PMID27505236 | DOI:10.1016/j.cub.2016.07.001 — OMIA Phene_Article / Article - 2016. Comparison of DMRT3 genotypes among American Saddlebred horses with reference to gait. Anim Genet — PubMed:PMID27295976 | DOI:10.1111/age.12458 — OMIA Phene_Article / Article - (23 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:614754 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [19]

Anglo-Arab (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Anglo-Arab (Horse) [13]

Appaloosa (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: Appaloosa (Horse) [4]

Appaloosa (Horse) — Ocular squamous cell carcinoma (hereditary; OMIA-verified breed predisposition)

Summary: “Squamous cell carcinoma (SCC) is the most common cancer of the equine eye, and is second to equine sarcoid as the most common tumor of the horse overall.... The Haflinger breed, developed in Austria and Northern Italy during the late 19th century, appears to be among those breeds overrepresented for this disease” (Bellone et al., 2017) {contributed by Meredith O’Connell, working under the guidance of Professor Ernie Bailey, 5 March 2019} [20]

Clin feat: “Squamous cell carcinoma (SCC) is a slow-growing malignant neoplasia of the skin, mucous membranes and mucocutaneous junctions. It is the most common tumor of the eye and adnexa in the horse. Most commonly, the nictitating membrane, nasal canthus, limbus and eyelids are affected. Untreated ocular SCC may invade local soft tissues, the bony orbit, sinuses and brain and less commonly, it may metastasize to the regional lymph nodes, salivary glands and thorax. Limbal involvement can quickly lead to visual impairment and destruction of the globe” (Kaps et al., 2005). {contributed by Meredith O’Connell, working under the guidance of Professor Ernie Bailey, 5 March 2019} [20]

Prevalence: For breeds in which SCC has been reported, the variant allele frequencies reported by Bellone et al. (2017) are 0.25 for Haflingers, 0.21 for Belgians, 0.20 for Rocky Mountain Horses, 0.07 for Percherons, 0.02 for Appaloosas, and zero for Arabian, Clydesdale, Dutch Warmblood, Hanoverian, Oldenburg, Paint Horse, Quarter Horse, Shire, and Thoroughbred. The breeds with zero variant frequency (but in which SCC has been reported) are indicative of the extent to which this variant is incompletely associated with SCC. Knickelbein et al. (2019) reported the frequency of the same variant in the Rocky Mountain breed to be 0.2. {much of the above information was contributed by Meredith O’Connell, working under the guidance of Professor Ernie Bailey, 5 March 2019} Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388942449 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 1996. Penetrating keratoplasty for treatment of recurrent squamous cell carcinoma of the cornea in a horse. Journal of the American Veterinary Medical Association — OMIA Phene_Article / Article - 2005. Primary invasive ocular squamous cell carcinoma in a horse. Vet Ophthalmol — PubMed:PMID15910373 | DOI:10.1111/j.1463-5224.2005.00358.x — OMIA Phene_Article / Article - 1991. Prognostic factors and survival of horses with ocular/adnexal squamous cell carcinoma: 147 cases (1978-1988). J Am Vet Med Assoc — PubMed:PMID2004996 — OMIA Phene_Article / Article - 1991. Epidemiologic study of ocular/adnexal squamous cell carcinoma in horses. J Am Vet Med Assoc — PubMed:PMID2004985 — OMIA Phene_Article / Article - 1987. Factors influencing morbidity and outcome of equine ocular squamous cell carcinoma. Equine Vet J — PubMed:PMID3608956 — OMIA Phene_Article / Article - 1978. Primary ocular squamous cell carcinoma with metastasis in a horse. Vet Med Small Anim Clin — PubMed:PMID247797 — OMIA Phene_Article / Article - 2017. A missense mutation in damage-specific DNA binding protein 2 is a genetic risk factor for limbal squamous cell carcinoma in horses. Int J Cancer — PubMed:PMID28425625 | DOI:10.1002/ijc.30744 — OMIA Phene_Article / Article - 2015. Limbal squamous cell carcinoma in Haflinger horses. Vet Ophthalmol — PubMed:PMID25312447 | DOI:10.1111/vop.12229 — OMIA Phene_Article / Article - 2017. Genetic testing as a tool to identify horses with or at risk for ocular disorders. Vet Clin North Am Equine Pract — PubMed:PMID29103563 | DOI:10.1016/j.cveq.2017.08.005 — OMIA Phene_Article / Article - 2018. Genetic risk for squamous cell carcinoma of the nictitating membrane parallels that of the limbus in Haflinger horses. Anim Genet — PubMed:PMID29999543 | DOI:10.1111/age.12695 — OMIA Phene_Article / Article - 2020. A missense mutation in damage-specific DNA binding protein 2 is a genetic risk factor for ocular squamous cell carcinoma in Belgian horses. Equine Vet J — PubMed:PMID30903710 | DOI:10.1111/evj.13116 — OMIA Phene_Article / Article - 2019. Limbal squamous cell carcinoma in a Rocky Mountain Horse: Case report and investigation of genetic contribution. Vet Ophthalmol — PubMed:PMID30238589 | DOI:10.1111/vop.12612 — OMIA Phene_Article / Article - (10 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:278740 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [20]

Appaloosa (Horse) — rhabdomyolysis with hyperthermia; anesthesia-induced malignant hyperthermia (hereditary; OMIA-verified breed predisposition)

Disorder: rhabdomyolysis with hyperthermia; anesthesia-induced malignant hyperthermia [21]

Summary: Malignant hyperthermia (MH) is a potentially life-threatening disorder in horses that can be triggered by halogenated anaesthetics and other non-aesthetic factors that may include exercise, stress, breeding, illnesses, and concurrent myopathies. It has an estimated mortality rate of 34% when halothane anaesthesia is administered (cited by Aleman et al., 2009). MH occurs primarily in Quarter horses, but has been reported in other breeds including Thoroughbred, Appaloosa, Arabian horses, and ponies (Aleman et al., 2004). Horses are generally mature before exhibiting clinical signs. [21]

Clin feat: “Mutations in the RYR1 gene cause dysfunction of the calcium release channel of the sarcoplasmic reticulum in skeletal muscle, resulting in excessive release of calcium into the myoplasm and a hypermetabolic state characterized by intense heat, hypercapnia [elevated carbon dioxide (CO2) levels in the blood], lactic acidosis, and, in many cases, death” (Aleman et al., 2004) Malignant hyperthermia episodes can include signs such as muscle contracture (rigidity), elevated body temperature, elevated heart rate, irregular heart rhythm, excessive sweating, and shallow breathing. Horses with the MH likely causal variant can exhibit more severe clinical symptoms if they also have a PSSM1 mutation (McCue et al., 2009) (see also OMIA 001158-9796: Polysaccharide storage myopathy/PSSM1/Exertional rhabdomyolysis in Equus caballus). [21]

Prevalence: Aleman et al. (2025) reported allele frequencies based on data from 159,227 horses from 16 breeds: The MH allele was exclusively detected in 391 QH, 18 Paints (PT), one Appaloosa (AP), and one QH-Clydesdale cross with similar allele frequencies (QH = 0.0013 and PT and AP = 0.0012). [21]

Gen test: Genetic testing for the reported likely causal variant is available. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4143652 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: By cloning and sequencing a very likely comparative candidate gene (based on the homologous disorder in other species, especially pigs and humans), Aleman et al. (2004) characterised the molecular basis of this disorder in two affected horses: a base substitution (C7360G) in exon 46 of the RyR1 gene results in an amino-acid substitution (R2454G). This codon is also mutated in two of the five exon-… Evidence (references) - 1992. Localization of the calcium release channel gene in cattle and horse by in situ hybridization - Evidence of a conserved synteny with glucose phosphate isomerase. Anim Genet — PubMed:PMID1315127 — OMIA Phene_Article / Article - 1994. Hyperthermia during isoflurane anaesthesia in a horse with suspected hyperkalaemic periodic paralysis. Equine Vet J — PubMed:PMID7889930 | DOI:10.1111/j.2042-3306.1994.tb04061.x — OMIA Phene_Article / Article - 2005. Malignant hyperthermia in a horse anesthetized with halothane. J Vet Intern Med — PubMed:PMID15954554 | DOI:10.1892/0891-6640(2005)19[363:mhiaha]2.0.co;2 — OMIA Phene_Article / Article - 2004. Association of a mutation in the ryanodine receptor 1 gene with equine malignant hyperthermia. Muscle Nerve — PubMed:PMID15318347 | DOI:10.1002/mus.20084 — OMIA Phene_Article / Article - 2009. A rapid detection method for the ryanodine receptor 1 (C7360G) mutation in Quarter Horses. J Vet Intern Med — PubMed:PMID19298609 | DOI:10.1111/j.1939-1676.2009.0281.x — OMIA Phene_Article / Article - 2009. Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in Quarter Horses. J Vet Intern Med — PubMed:PMID19220734 | DOI:10.1111/j.1939-1676.2009.0274.x — OMIA Phene_Article / Article - 2009. Polysaccharide storage myopathy phenotype in quarter horse-related breeds is modified by the presence of an RYR1 mutation. Neuromuscul Disord — PubMed:PMID19056269 | DOI:10.1016/j.nmd.2008.10.001 — OMIA Phene_Article / Article - 1983. Succinylcholine infusion associated with hyperthermia in ponies anesthetized with halothane. Am J Vet Res — PubMed:PMID6660617 — OMIA Phene_Article / Article - 1981. Malignant hyperthermia in a halothane-anesthetized horse. J Am Vet Med Assoc — PubMed:PMID7341603 — OMIA Phene_Article / Article - 1989. Postanesthetic equine myopathy suggestive of malignant hyperthermia. A case report. Vet Surg — PubMed:PMID2603379 | DOI:10.1111/j.1532-950x.1990.tb01131.x — OMIA Phene_Article / Article - 1983. Malignant hyperthermia-like reactions in three anesthetized horses. J Am Vet Med Assoc — PubMed:PMID6874529 — OMIA Phene_Article / Article - 1985. Unusual response following use of succinylcholine in a horse anesthetized with halothane. J Am Vet Med Assoc — PubMed:PMID4055481 — OMIA Phene_Article / Article - (9 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:145600 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:180901 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [21]

Arab (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Arab (Horse) [22]

Clin feat: Brault et al. 2011 (Genomics): Cerebellar abiotrophy (CA) is a neurological condition, characterized by post-natal degeneration of Purkinje cells of the cerebellum... Symptoms of CA in horses generally appear between six weeks and four months of age and include intention head tremors, ataxia, exaggerated or paddling action of the forelegs, a wide-based stance and a lack of menace response.... Affected horses may startle easily and fall, and are often unable to rise from a reclining position”. {slightly modified from text provided by Meredith O’Connell, working under the supervision of Professor E. Bailey} [22]

Prevalence: Other than the strong prevalence known in Arabians, “At least one CA carrier was identified in 3 breeds and the frequency of the CA allele calculated: Bashkir Curly Horses (2.8%), Trakehners (0.68%) and Welsh ponies (0.33%). Based on pedigree and haplotype analysis, CA was introduced into these breeds by Arabian ancestry. The Trakehner and Welsh pony carriers were at least half-Arabian, while the Bashkir Curly horses appeared to have had the CA allele introduced by a single Arabian stallion used for developing the breed in the 1960s” (Brault, et al., EVJ, 2011). {text provided by Meredith O’Connell, working under the supervision of Professor E. Bailey} Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4155602 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - Gene: Entrez Gene ID 388943623 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: “The CA region contains four annotated genes, including MUTYH and TOE1, both of which are potential candidate genes. . . . One SNP identified [ECA2:13074277G>A as reported in this paper] was found to be exclusive to the Arabian breed and to be completely concordant with the CA trait, making it an excellent candidate for the CA mutation. This SNP is located in exon 4 of TOE1 but results in a rel… Evidence (references) - 1973. Cerebellar hypoplasia and degeneration in the young Arab horses: clinical and neuropathological features. Vet Rec — PubMed:PMID4748678 | DOI:10.1136/vr.93.3.62 — OMIA Phene_Article / Article - 1974. Cerebellar hypoplasia and degeneration in part Arab horses. Aust Vet J — PubMed:PMID4819469 | DOI:10.1111/j.1751-0813.1974.tb09367.x — OMIA Phene_Article / Article - 1995. Cerebellar abiotrophy in pure-bred arabians [German]. Pferdeheilkunde — OMIA Phene_Article / Article - 2011. Mapping of equine cerebellar abiotrophy to ECA2 and identification of a potential causative mutation affecting expression of MUTYH. Genomics — PubMed:PMID21126570 | DOI:10.1016/j.ygeno.2010.11.006 — OMIA Phene_Article / Article - 1987. Cerebellar abiotrophy. Vet Clin North Am Equine Pract — PubMed:PMID3497695 | DOI:10.1016/s0749-0739(17)30677-6 — OMIA Phene_Article / Article - 2006. Purkinje cell apoptosis in arabian horses with cerebellar abiotrophy. J Vet Med A Physiol Pathol Clin Med — PubMed:PMID16901270 | DOI:10.1111/j.1439-0442.2006.00836.x — OMIA Phene_Article / Article - 2011. Inheritance of cerebellar abiotrophy in Arabians. Am J Vet Res — PubMed:PMID21728855 | DOI:10.2460/ajvr.72.7.940 — OMIA Phene_Article / Article - 2011. The frequency of the equine cerebellar abiotrophy mutation in non-Arabian horse breeds. Equine Vet J — PubMed:PMID21496100 | DOI:10.1111/j.2042-3306.2010.00349.x — OMIA Phene_Article / Article - 2013. Morphometric magnetic resonance imaging and genetic testing in cerebellar abiotrophy in Arabian horses. BMC Vet Res — PubMed:PMID23702154 | DOI:10.1186/1746-6148-9-105 — OMIA Phene_Article / Article - 2017. Defining Trends in Global Gene Expression in Arabian Horses with Cerebellar Abiotrophy. Cerebellum — PubMed:PMID27709457 | DOI:10.1007/s12311-016-0823-8 — OMIA Phene_Article / Article - 2016. First report of cerebellar abiotrophy in an Arabian foal from Argentina. Open Vet J — PubMed:PMID28116251 | DOI:10.4314/ovj.v6i3.17 — OMIA Phene_Article / Article - 2014. The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Vet J — PubMed:PMID24033554 | DOI:10.1111/evj.12177 — OMIA Phene_Article / Article - (11 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:600224 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [22]

Arab (Horse) — Myopathy, myofibrillar (hereditary; OMIA-verified breed predisposition)

Mode of inheritance: Williams et al. (2020):. a potential familial basis for MFM has been suggested by the presence of desmin aggregates in a 3‐generation family of WB [Valberg et al. 2017]. [23]

Clin feat: Williams et al. (2020): Clinical signs associated with MFM WB are usually apparent by 11 years of age and include exercise intolerance, a reluctance to move forward under saddle and a mild lameness not attributable to an underlying orthopaedic cause. [23]

Pathology: Valberg et al. (2017): Abnormal aggregates of the cytoskeletal protein desmin were found in up to 120 type 2a and a few type 2x myofibres of MFM cases. Desmin positive fibres did not stain for developmental myosin, α actinin or dystrophin. Scores for internalised myonuclei (score MFM 0.83 ± 0.67, controls 0.22 ± 0.45), anguloid atrophy (MFM 0.95 ± 0.55, controls 0.31 ± 0.37) and total myopathic scores (MFM 5.85 ± 2.10, controls 1.41 ± 2.17) were significantly higher in MFM cases vs. controls. Focal Z disc degeneration, myofibrillar disruption and accumulation of irregular granular material was evident in MFM cases. Muscle glycogen concentrations were similar between MFM cases and controls. In the Warmblood family, desmin positive aggregates were found in myofibres of the founding dam and in horses from two subsequent generations. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA entry symbol: MFM (no structured Phene_Gene link) - OMIA molecular-genetics note: Williams et al. (2020): "Variants identified in MFM candidate genes, including two coding variants offered as commercial MFM equine genetic tests, did not associate with the WB MFM phenotype." Evidence (references) - 2017. Clinical characteristics and muscle glycogen concentrations in warmblood horses with polysaccharide storage myopathy. Am J Vet Res — PubMed:PMID29076373 | DOI:10.2460/ajvr.78.11.1305 — OMIA Phene_Article / Article - 2018. Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy. PLoS One — PubMed:PMID30183782 | DOI:10.1371/journal.pone.0203467 — OMIA Phene_Article / Article - 2017. Clinical and histopathological features of myofibrillar myopathy in Warmblood horses. Equine Vet J — PubMed:PMID28543538 | DOI:10.1111/evj.12702 — OMIA Phene_Article / Article - 2021. Candidate gene expression and coding sequence variants in Warmblood horses with myofibrillar myopathy. Equine Vet J — PubMed:PMID32453872 | DOI:10.1111/evj.13286 — OMIA Phene_Article / Article - 2021. Integrated proteomic and transcriptomic profiling identifies aberrant gene and protein expression in the sarcomere, mitochondrial complex I, and the extracellular matrix in Warmblood horses with myofibrillar myopathy. BMC Genomics — PubMed:PMID34112090 | DOI:10.1186/s12864-021-07758-0 — OMIA Phene_Article / Article - 2023. Absence of myofibrillar myopathy in Quarter Horses with a histopathological diagnosis of type 2 polysaccharide storage myopathy and lack of association with commercial genetic tests. Equine Vet J — PubMed:PMID35288976 | DOI:10.1111/evj.13574 — OMIA Phene_Article / Article - 2025. Myofibrillar myopathy. Vet Clin North Am Equine Pract — PubMed:PMID39880730 | DOI:10.1016/j.cveq.2024.11.005 — OMIA Phene_Article / Article - 2025. Sporadic and recurrent exertional rhabdomyolysis. Vet Clin North Am Equine Pract — PubMed:PMID39880734 | DOI:10.1016/j.cveq.2024.11.003 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:603689 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:601419 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:617114 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:609200 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:609524 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:619040 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:609452 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:612954 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:613869 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:608810 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:617258 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:619178 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [23]

Arab (Horse) — Severe Combined Immunodeficiency Disease (SCID) (hereditary; OMIA-verified breed predisposition)

Disorder: Severe Combined Immunodeficiency Disease (SCID) [24]

Clin feat: Affected foals are clinically normal at birth but beginning at about 10 days of age they develop a range of clinical signs, particularly bronchopneumonia and diarrhea with which adenoviruses are peculiarly associated (Studdert, 1978). {with thanks to Meredith O’Connell, Tanya German, Isabella Pisani and Karalie Andrews, working under the guidance of Professor Ernie Bailey; 25 Feb 2019} The combined nature of this disorder was highlighted by McGuire and Poppie (1973): “The defect in the B-lymphocyte system was shown by hypogammaglobulinemia, lymphopenia and absence of germinal centers. The almost total absence of thymic tissue in one foal and the lack of thymic dependent lymphocytes in the spleens of both foals demonstrate a T-cell defect.” {with thanks to Professor E. Bailey; 20 March 2019} [24]

Prevalence: AbouEl Ela et al. (2018) reported a zero frequency of the c.9478_9482del variant in a sample of 103 Egyptian horses, including 33 randomly-selected Arab horses. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: DNA-PK (Entrez Gene ID 40417433) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: The molecular basis of SCID in horses was discovered by Shin et al. (1997), who used the comparative candidate-gene approach (based on work with SCID mice; see Mapping section). By sequencing the equine homologue of DNAPK, Shin et al. (1997) showed that SCID in horses is due to a 5bp deletion giving rise to a frameshift in that gene, resulting in the lack of full-length kinase, and absence of kina… Evidence (references) - 1978. Mixed lymphocyte culture responses in combined immunodeficiency of horses. Transplantation — PubMed:PMID146281 — OMIA Phene_Article / Article - 1980. Combined immunodeficiency of Arabian horses: Confirmation of autosomal recessive mode of inheritance. Journal of the American Veterinary Medical Association — PubMed:PMID7429919 — OMIA Phene_Article / Article - 1980. Immunologic aspects of combined immunodeficiency disease in Arabian foals. Am J Vet Res — PubMed:PMID7004276 — OMIA Phene_Article / Article - 1974. Combined (B- and T-lymphocyte) immunodeficiency: a fatal genetic disease in Arabian foals. Journal of the American Veterinary Medical Association — PubMed:PMID4358832 — OMIA Phene_Article / Article - 1977. Combined immunodeficiency in foals of Arabian breeding: evaluation of mode of inheritance and estimation of prevalence of affected foals and carrier mares and stallions. Journal of the American Veterinary Medical Association — PubMed:PMID299745 — OMIA Phene_Article / Article - 1978. Legal aspects of diagnosing combined immunodeficiency (CID) in Arabian foals. American Association of Equine Practitioners Newsletter — OMIA Phene_Article / Article - 1978. Primary, severe, combined immunodeficiency disease of Arabian foals. Aust Vet J — PubMed:PMID217327 | DOI:10.1111/j.1751-0813.1978.tb05562.x — OMIA Phene_Article / Article - 1975. Surface receptors on neutrophils and monocytes from immunodeficient and normal horses. Immunology — PubMed:PMID1126740 — OMIA Phene_Article / Article - 1989. Bone Marrow Transplantation in Horses with Hereditary Severe Combined Immunodeficiency — OMIA Phene_Article / Article - 1990. Concurrent Cryptosporidium and Coronavirus Infections in an Arabian Foal with Combined Immunodeficiency Syndrome. Veterinary Record — PubMed:PMID2156372 — OMIA Phene_Article / Article - 1989. Serum Uric Acid Concentrations in Horses Heterozygous for Combined Immunodeficiency. American Journal of Veterinary Research — PubMed:PMID2610446 — OMIA Phene_Article / Article - 1991. Persistent Cryptosporidiosis in Horses with Severe Combined Immunodeficiency. Infection and Immunity — PubMed:PMID1894380 — OMIA Phene_Article / Article - (54 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:600899 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:615966 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [24]

Ardennes (Horse) — Silver dapple (hereditary; OMIA-verified breed predisposition)

Breed: Ardennes (Horse) [5]

Bashkir Curly (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Bashkir Curly (Horse) [22]

Bashkir Curly (Horse) — Curly coat, KRT25-related (hereditary; OMIA-verified breed predisposition)

Summary: Morgenthaler et al. (2017): First described by Crow and Sioux Native American tribes as early as 1801 during winter horse counting [Thomas et al., 1989], Curly horses present a variety of coat curl phenotypes associated with diverse degrees of curliness which can range from “minimal” scattered curled hair up to extremely dense “micro curled” permanent coat as observed in certain Missouri Fox Trotter lines. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388944862 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Morgenthaler et al. (2017): "whole-genome sequences were obtained for one heterozygous curly stallion and its straight-haired son. Among the four non-synonymous candidate variants identified and validated in the curly region, only variant g.21891160G>A in the KRT25 gene (KRT25:p.R89H) [omia.variant:856] was in perfect agreement with haplotype status in the whole pedigree. Genetic assoc… Evidence (references) - 1940. Inheritance of curliness in the horse. C.R. (Doklady) Academy of Science U.R.S.S., N.S. — OMIA Phene_Article / Article - 1990. Dominant Curly Coat in Horses. Genetics Selection Evolution — OMIA Phene_Article / Article - 2016. Rare phenotypes in domestic animals: unique resources for multiple applications. Anim Genet — PubMed:PMID26662214 | DOI:10.1111/age.12393 — OMIA Phene_Article / Article - 2017. A missense variant in the coil1A domain of the keratin 25 gene is associated with the dominant curly hair coat trait (Crd) in horse. Genet Sel Evol — PubMed:PMID29141579 | DOI:10.1186/s12711-017-0359-5 — OMIA Phene_Article / Article - 1989. Myth and mystery: the curly horse in America. New York: C.S. Fund Inc. — OMIA Phene_Article / Article - 1943. Curly coat of horses. Journal of Heredity — OMIA Phene_Article / Article - 2018. An epistatic effect of KRT25 on SP6 is involved in curly coat in horses. Sci Rep — PubMed:PMID29686323 | DOI:10.1038/s41598-018-24865-3 — OMIA Phene_Article / Article - 2024. Horse allergy: Curly Horses can mediate immune tolerance. Pneumologie — PubMed:PMID37827498 | DOI:10.1055/a-2101-9533 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:616760 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:616646 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [25]

Belgian Draft (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Belgian Draft (Horse) [17]

Belgian Draft (Horse) — Hydrocephalus (hereditary; OMIA-verified breed predisposition)

Clin feat: “Hydrocephalus is defined as ‘an active distension of the ventricular system of the brain resulting from inadequate passage of cerebrospinal fluid (CSF) from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation...’ Hydrocephalus can be acquired, e.g. due to infection or trauma, or can be hereditary in nature. To our best knowledge, no clear cases of a proven acquired hydrocephalus in horses have been reported in scientific literature. Different types of hydrocephalus have been identified based on the underlying mechanisms: communicating (increased production or impaired CSF absorption) or non-communicating (obstruction in CSF flow).... Also, hydrocephalus can be internal or external, that is an accumulation of CSF respectively within or outside the ventricles of the brain. In horses, both external and internal hydrocephalus... have been diagnosed” (Ducro et. al, 2015). {Text provided by Meredith O’Connell, working under the supervision of Professor Ernie Bailey; 24 April 2019} [26]

Prevalence: “Out of 60 stallions that were genotyped using a commercially available DNA test based on the B3GALNT2 mutation, 8 (13.3 %) were carrier of the allele T. Out of 805 broodmares, 139 (17.3 %) were also carrier.” (Ducro et al., 2015). As the authors reported, this gives a frequency of the likely causal variant of 8.5%. {Adapted by FN from text provided by Meredith O’Connell, working under the supervision of Professor Ernie Bailey; 24 April 2019} Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388948668 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Ducro et al. (2015) reported that "Next generation DNA sequence analysis of 4 cases and 6 controls of gene exons within the [candidate] region [see Mapping section] revealed a [nonsense] mutation in β-1,3-N-acetylgalactosaminyltransferase 2 (B3GALNT2) as the likely cause of hydrocephalus in Friesian horses. The nonsense mutation XM_001491545 c.1423C>T corresponding to XP_001491595 p.Gln475* was… Evidence (references) - 1993. Diffuse Cerebral Encephalopathy Associated with Hydrocephalus and Cholesterinic Granulomas in a Horse. Journal of the American Veterinary Medical Association — PubMed:PMID8407539 — OMIA Phene_Article / Article - 1996. Cervical meningomyelocele associated with spina bifida in a hydrocephalic miniature colt. Journal of the American Veterinary Medical Association — OMIA Phene_Article / Article - 2002. A case of hydrocephalus in a Polish Primitive Horse. Medycyna Weterynaryjna — OMIA Phene_Article / Article - 2011. Diagnosis of internal and external hydrocephalus in a warmblood foal using magnetic resonance imaging. Tierarztl Prax Ausg G Grosstiere Nutztiere — PubMed:PMID22138744 — OMIA Phene_Article / Article - 1992. Inheritance of hydrocephalus in horses. Equine Vet J — PubMed:PMID1582393 — OMIA Phene_Article / Article - 1980. Congenital hydrocephalus in 2 foals. Mod Vet Pract — PubMed:PMID7421786 — OMIA Phene_Article / Article - 1979. A case of equine hydrocephalus. N Z Vet J — PubMed:PMID291822 | DOI:10.1080/00480169.1979.34633 — OMIA Phene_Article / Article - 1976. Hydrocephalus in an 18-month-old colt. J Am Vet Med Assoc — PubMed:PMID931772 — OMIA Phene_Article / Article - 1950. [Hydrocephalus of the colt]. Rec Med Vet Ec Alfort — PubMed:PMID14781419 — OMIA Phene_Article / Article - 2013. Phenotypic characteristics of hydrocephalus in stillborn Friesian foals. Vet Pathol — PubMed:PMID23676552 | DOI:10.1177/0300985813488955 — OMIA Phene_Article / Article - 2015. A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses. BMC Genomics — PubMed:PMID26452345 | DOI:10.1186/s12864-015-1936-z — OMIA Phene_Article / Article - 2017. Genotyping of friesian horses to detect a hydrocephalus-associated c.1423C>T mutation in B3GALNT2 using PCR-RFLP and PCR-PIRA methods: Frequency in stallion horses in México. Mol Cell Probes — PubMed:PMID28011345 | DOI:10.1016/j.mcp.2016.12.005 — OMIA Phene_Article / Article - (5 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:109400 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:112240 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:123155 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:209970 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236600 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236635 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236640 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236660 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236670 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:236690 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:273730 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:276950 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:307000 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:307010 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:314390 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:123155 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600257 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600559 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600991 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:615181 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [26]

Belgian Draft (Horse) — Junctional epidermolysis bullosa (hereditary; OMIA-verified breed predisposition)

Disorder: Junctional epidermolysis bullosa [27]

Summary: Several cases of junctional epidermolysis bullosa (JEB) were described for Belgian draft horse foals and similarity to a condition in humans was identified (Frame et al., 1988; Johnson et al. 1988; Kohn et al., 1989; Shapiro and McEwen, 1995). A likely causal variant was identified in the LAMC2 gene (Spirito et al., 2002). The same variant was later reported to cause JEB in the Trait Briton and the Trait Comtois draft horses in France (Milenkovic et al., 2003), and in an Italian draft horse (Cappelli et al., 2015). [27]

Clin feat: Lesions can be present at birth or develop over a short period of time and are characterized by the development of vesicles and bullae that rapidly progress to erosions and ulcerations at sites of minor trauma such as the lips, the oral mucosa, and distal extremities and the coronary band, with resulting sloughing of the hoofs.. Lesions can be secondarily affected or become pustules. Affected animals may die soon after birth due to inability to suckle.“ (Capelli et al. 2015) [27]

Pathology: Spirito et al. (2002): Electron microscopy examination revealed junctional blistering and abnormal hemidesmosomes (Johnson et al., 1988) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 3645968 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 1988. Hereditary junctional mechanobullous disease in a foal. Journal of the American Veterinary Medical Association — PubMed:PMID3209456 — OMIA Phene_Article / Article - 1995. Mechanobullous disease in a Belgian foal in eastern Ontario. Canadian Veterinary Journal — OMIA Phene_Article / Article - 1989. Mechanobullous disease in two Belgian foals. Equine Veterinary Journal — PubMed:PMID2767032 — OMIA Phene_Article / Article - 1988. Ultrastructure of junctional epidermolysis bullosa in Belgian foals. J Comp Pathol — PubMed:PMID3204167 | DOI:10.1016/0021-9975(88)90053-9 — OMIA Phene_Article / Article - 2003. A mutation in the LAMC2 gene causes the Herlitz junctional epidermolysis bullosa (H-JEB) in two French draft horse breeds. Genetics Selection Evolution — PubMed:PMID12633536 | DOI:10.1051/gse:2003007 — OMIA Phene_Article / Article - 2002. Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse. J Invest Dermatol — PubMed:PMID12230513 | DOI:10.1046/j.1523-1747.2002.01852.x — OMIA Phene_Article / Article - 2003. Junctional epidermolysis bullosa in Belgian draft horses. Proc Am Assoc Equine Practnr — OMIA Phene_Article / Article - 2015. First report of junctional epidermolysis bullosa (JEB) in the Italian draft horse. BMC Vet Res — PubMed:PMID25889423 | DOI:10.1186/s12917-015-0374-0 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:226700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:226650 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:150292 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [27]

Belgian Draft (Horse) — myosin heavy chain myopathy (hereditary; OMIA-verified breed predisposition)

Disorder: myosin heavy chain myopathy [28]

Clin feat: Finno et al. (2018): immune-mediated myositis (IMM) [is]... characterized by recurrent, rapid-onset muscle atrophy in Quarter Horses (QH) [28]

Pathology: Finno et al. (2018): The histopathologic hallmark of IMM is lymphocytic infiltration of myofibers. [28]

Prevalence: Gianino et al. (2019): The E321G MYH1 variant allele frequency was 0.034 ± 0.011 in the general QH population (6.8% of individuals in the breed) and the highest among the reining (0.135 ± 0.040; 24.3% of reiners), working cow (0.085 ± 0.031), and halter (0.080 ± 0.027) performance subgroups. The E321G MYH1 variant was present in cutting (0.044 ± 0.022) and Western Pleasure (0.021 ± 0.015) QHs at lower frequency and was not observed in barrel racing or racing QHs. Knowing that reining and working cow QHs have the highest prevalence of the E321G MYH1 variant and that the variant is more prevalent than the alleles for hereditary equine regional dermal asthenia and hyperkalemic periodic paralysis in the general QH population will guide the use of genetic testing for diagnostic and breeding purposes. Albuquerque et al. (2022) “report of two related QH foals with the E321G MYH1 mutation that had clinical signs of MYHM, with histological confirmation of IMM in one of the foals. This prompted an investigation the aim of which was to determine the allele frequency of the E321G MYH1 variant across QHs using a DNA archive in Brazil. … Of the 299 genotyped QHs, 44 animals (14.7%) were heterozygous (My/N) for the E321G MYH1 variant, and 255 (85.3%) were homozygous for the wild-type allele (N/N), implying an allele frequency of 0.074.” [28]

Gen test: Finno et al. (2018) concluded that their results suggest that rather than consistently causing a myopathy, homozygosity and, in some cases, heterozygosity for the MYH1 variant predisposed horses to a myopathy under certain environmental triggers. In other words, the jury is still undecided in relation to the utility of genotyping for this variant as a means of selecting against the disorder. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: MYHC-2X (Entrez Gene ID 388391246) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Finno et al. (2018) reported that "Whole genome sequencing of four IMM and four unaffected QHs identified a single segregating nonsynonymous E321G mutation in [a positional candidate gene] MYH1 encoding myosin heavy chain 2X. Genotyping of additional 35 IMM and 22 unaffected QHs confirmed an association (P = 2.9 × 10− 5), and the putative mutation was absent in 175 horses from 21 non-QH breeds." Evidence (references) - 2007. Suspected immune-mediated myositis in horses. J Vet Intern Med — PubMed:PMID17552457 | DOI:10.1892/0891-6640(2007)21[495:simih]2.0.co;2 — OMIA Phene_Article / Article - 2018. Immune-Mediated Muscle Diseases of the Horse. Vet Pathol — PubMed:PMID28129093 | DOI:10.1177/0300985816688755 — OMIA Phene_Article / Article - 2018. A missense mutation in MYH1 is associated with susceptibility to immune-mediated myositis in Quarter Horses. Skelet Muscle — PubMed:PMID29510741 | DOI:10.1186/s13395-018-0155-0 — OMIA Phene_Article / Article - 2019. Prevalence of the E321G MYH1 variant for immune-mediated myositis and nonexertional rhabdomyolysis in performance subgroups of American Quarter Horses. J Vet Intern Med — PubMed:PMID30623495 | DOI:10.1111/jvim.15393 — OMIA Phene_Article / Article - 2022. Prevalence of the E321G MYH1 variant in Brazilian Quarter horses. Equine Vet J — PubMed:PMID34606642 | DOI:10.1111/evj.13521 — OMIA Phene_Article / Article - 2021. Myofibre hyper-contractility in horses expressing the myosin heavy chain myopathy mutation, MYH1 E321G. Cells — PubMed:PMID34943936 | DOI:10.3390/cells10123428 — OMIA Phene_Article / Article - 2022. Prevalence of clinical signs and factors impacting expression of myosin heavy chain myopathy in Quarter Horse-related breeds with the MYH1 E321G mutation. J Vet Intern Med — PubMed:PMID35426178 | DOI:10.1111/jvim.16417 — OMIA Phene_Article / Article - 2022. Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci — PubMed:PMID36150530 | DOI:10.1016/j.jevs.2022.104129 — OMIA Phene_Article / Article - 2024. Myosin heavy-chain myopathy in 2 American quarter horses. Vet Pathol — PubMed:PMID37818977 | DOI:10.1177/03009858231204253 — OMIA Phene_Article / Article - 2024. Allele frequency of muscular genetic disorders in bull-catching (vaquejada) quarter horses. J Equine Vet Sci — PubMed:PMID38531516 | DOI:10.1016/j.jevs.2024.105052 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Inflammatory and immune-mediated myopathies, what do we know?. Vet Clin North Am Equine Pract — PubMed:PMID38852014 | DOI:10.1016/j.cveq.2024.05.003 — OMIA Phene_Article / Article - (4 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:160750 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:160730 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [28]

Berber, Germany (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Berber, Germany (Horse) [13]

Bhotia Pony, India (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Bhotia Pony, India (Horse) [19]

Black Forest (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Black Forest (Horse) [17]

Breton, France (Horse) — Junctional epidermolysis bullosa (hereditary; OMIA-verified breed predisposition)

Breed: Breton, France (Horse) [27]

British Spotted Pony, Spotted Pony, United Kingdom of Great Britain and Northern Ireland (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: British Spotted Pony, Spotted Pony, United Kingdom of Great Britain and Northern Ireland (Horse) [4]

CH-Warmblut, Switzerland (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: CH-Warmblut, Switzerland (Horse) [13]

Camarillo White Horse, United States of America (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Camarillo White Horse, United States of America (Horse) [13]

Caspian (Horse) — Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (hereditary; OMIA-verified breed predisposition)

Breed: Caspian (Horse) [29]

Disorder: Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy [29]

Mode of inheritance: Posbergh et al. (2018): The ABD [autozygosity by difference] score difference pattern suggests an autosomal recessive pattern of inheritance [in the Caspian breed]... [but]... the recessive inheritance pattern seen here contrasts with other studies of EDM in other breeds. [29]

Clin feat: Marquardt et al. (2019): Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is a neurologic disease that has been reported in young horses from a wide range of breeds. Equine degenerative myeloencephalopathy (EDM) is a more histologically advanced form of equine neuroaxonal dystrophy (eNAD). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA entry symbol: eNAD/EDM (no structured Phene_Gene link) - OMIA molecular-genetics note: Posbergh et al. (2018) reported a positional candidate missense SNP in the ADGRL3 gene at ECA3:71770084; c.?A>G; p.Asn?Ser. Noting that the only two surviving homozygotes for this variant within this breed do not show any clinical signs, Posbergh et al. (2018) cautiously described the variant as "a genetic risk factor, working in conjunction with environmental factors, in the development of the… Evidence (references) - 1988. Current research topics in Equine Genetics, Part 2. Equine Practice — OMIA Phene_Article / Article - 1990. Factors associated with the development of equine degenerative myeloencephalopathy. Am J Vet Res — PubMed:PMID2386332 — OMIA Phene_Article / Article - 1991. Clinical, viral, and genetic evaluation of equine degenerative myeloencephalopathy in a family of Appaloosas. J Am Vet Med Assoc — PubMed:PMID2032902 — OMIA Phene_Article / Article - 1992. Equine Degenerative Myeloencephalopathy .2. Diagnosis and Treatment. Compendium on Continuing Education for the Practicing Veterinarian — OMIA Phene_Article / Article - 1996. Equine degenerative myeloencephalopathy. Vlaams Diergeneeskundig Tijdschrift — OMIA Phene_Article / Article - 1997. Equine degenerative myeloencephalopathy. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 2011. Equine degenerative myeloencephalopathy in Lusitano horses. J Vet Intern Med — PubMed:PMID22092640 | DOI:10.1111/j.1939-1676.2011.00817.x — OMIA Phene_Article / Article - 2017. Pigment retinopathy in warmblood horses with equine degenerative myeloencephalopathy and equine motor neuron disease. Vet Ophthalmol — PubMed:PMID27491953 | DOI:10.1111/vop.12417 — OMIA Phene_Article / Article - 2018. A nonsynonymous change in adhesion G protein–coupled receptor L3 associated with risk for equine degenerative myeloencephalopathy in the Caspian horse. Journal of Equine Veterinary Science — DOI:10.1016/j.jevs.2018.08.010 — OMIA Phene_Article / Article - 2019. Concern regarding the publication by Posbergh et al. "A nonsynonymous change in adhesion G protein-coupled receptor L3 associated with risk for equine degenerative myeloencephalopathy in the Caspian horse," J Equine Vet Sci 2018;70:96-100. J Equine Vet Sci — PubMed:PMID30929777 | DOI:10.1016/j.jevs.2018.10.021 — OMIA Phene_Article / Article - 2019. Response to: "Concern Regarding the Publication by Posbergh et al". J Equine Vet Sci — PubMed:PMID30929776 | DOI:10.1016/j.jevs.2018.10.022 — OMIA Phene_Article / Article - 2019. Previously identified genetic variants in ADGRL3 are not associated with risk for equine degenerative myeloencephalopathy across breeds. Genes (Basel) — PubMed:PMID31491999 | DOI:10.3390/genes10090681 — OMIA Phene_Article / Article - (5 additional references in OMIA) [29]

Cavall Menorquí, Spain (Horse) — Splashed white, macchiato (hereditary; OMIA-verified breed predisposition)

Breed: Cavall Menorquí, Spain (Horse) [6]

Cavallo Agricolo Italiano da Tiro Pesante Rapido, Italy (Horse) — Junctional epidermolysis bullosa (hereditary; OMIA-verified breed predisposition)

Breed: Cavallo Agricolo Italiano da Tiro Pesante Rapido, Italy (Horse) [27]

Chakouyi, China (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Chakouyi, China (Horse) [19]

Clydesdale (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Clydesdale (Horse) [17]

Comtois (Horse) — Junctional epidermolysis bullosa (hereditary; OMIA-verified breed predisposition)

Breed: Comtois (Horse) [27]

Connemara Pony (Horse) — Also known as Hoof Wall Separation Disease (hereditary; OMIA-verified breed predisposition)

Breed: Connemara Pony (Horse) [30]

Disorder: Also known as Hoof Wall Separation Disease [30]

Clin feat: Hoof Wall Separation Disease (HWSD) is a disease that affects the Connemara Pony, a breed known for their strong, hearty hooves. HWSD is classified primarily by its clinical signs of a receding dorsal hoof wall and secondary solar proliferation. This disease differs from other causes of separation (e.g. White Line Disease, Abscessation, etc.) because the sole and white line both appear healthy, with the exception of the proliferative sole. (FN thanks Daniel J. Schmidt, who provided the basis of this contribution, working under the supervision of Professor Ernie Bailey; 16 April 2020) [30]

Prevalence: Within the entire 423-Connemara-pony data set, allele frequency was 18.7% and a total of 96 ponies were heterozygous for the SERPINB11 insertion. The heterozygous animals are all phenotypically unaffected by HWSD. Within a 324-pony subset of individuals unrelated to the affected animals, carrier frequency for the variant is 14.8%. The variant was not found among 169 horses of other unspecified breeds (Finno et al., 2015). (FN thanks Daniel J. Schmidt, who provided the basis of this contribution, working under the supervision of Professor Ernie Bailey; 16 April 2020) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388942681 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Whole-genome next-generation sequencing was conducted on 4 Connemara Ponies (2 cases, 2 control). The variants in the candidate region (see Mapping section above) were evaluated in a larger sample of Connemara Ponies, and a non-synonymous variant within the gene SERPINB11 was identified as the most likely cause of the trait, namely g.83600643_83600644insC (updated to Equcab 3.0) which introduces a… Evidence (references) - 2013. A successful genome wide association for Connemara Hoof Wall Separation Syndrome using the Equine Illumina 74K Beadchip. 10th Dorothy Russell Havemeyr Foundation International Equine Genome Mapping Workshop, Azores, Portugal. — OMIA Phene_Article / Article - 2015. SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara ponies. PLoS Genet — PubMed:PMID25875171 | DOI:10.1371/journal.pgen.1005122 — OMIA Phene_Article / Article - 2022. Hoof wall separation disease: A Review. Equine Vet Educ — PubMed:PMID36172455 | DOI:10.1111/eve.13530 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:615682 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [30]

Curly Horse (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Curly Horse (Horse) [18]

Dales (Horse) — Foal immunodeficiency syndrome in Fell and Dales Pony; Fell pony syndrome (hereditary; OMIA-verified breed predisposition)

Breed: Dales (Horse) [31]

Disorder: Foal immunodeficiency syndrome in Fell and Dales Pony; Fell pony syndrome [31]

Summary: Fox-Clipsham et al. (2011) [Vet Rec]: The Fell and Dales are UK pony breeds that have small populations.. Foal immunodeficiency syndrome (FIS) is a lethal inherited disease caused by the recessive mutation of a single gene, which affects both Fell and Dales ponies and potentially other breeds that have interbred with either of these. FIS. is characterised by progressive anaemia and severe B lymphocyte deficiency. The identification of the causal mutation for this disease led to the. development of a DNA-based carrier test. [31]

Clin feat: Foals with FIS appear to be normal at birth, but present with progressive anaemia as well as diarrhea, pneumonia, or other infectious diseases within a few weeks of age (Scholes et al., 1998). After an initial response to treatment, infections reoccur (Thomas et al., 2005). Foals either die or are humanely euthanized before three months of age. [31]

Pathology: Fox-Clipsham et al., 2011 [Vet Rec]: The underlying pathology. has been shown to be anaemia (Dixon et al., 2000; Richards et al., 2000), which is unrelated to blood loss or haemolysis, and a severe B lymphocyte deficiency (Thomas et al., 2003) with reduced antibody production (Thomas et al., 2005). Reduced antibody levels in affected foals cause an inability to generate an adaptive immune response, resulting in immunodeficiency once colostrum derived antibodies decrease at 3-6 weeks of age (Dixon et al., 2000). [31]

Prevalence: Fox-Clipsham et al. (2011) [Vet Rec] screened several breeds using the DNA-based carrier test to estimate carrier frequency for 2009/2010: approximately 40 per cent of adult UK Fell ponies and 20 per cent of adult UK Dales ponies carried the FIS defect.. [N]o FIS carriers were identified among the Clydesdale, Exmoor, Highland or Welsh section D samples.. [O]f the 192 coloured horse and pony samples. two were confirmed as carriers of FIS. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 40940161 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 2001. An immunodeficiency in Fell ponies: a preliminary study into cellular responses. Equine Veterinary Journal — PubMed:PMID11770991 — OMIA Phene_Article / Article - 2005. Immunoglobulin and peripheral B-lymphocyte concentrations in Fell pony foal syndrome. Equine Vet J — PubMed:PMID15651734 — OMIA Phene_Article / Article - 2006. Severe combined immunodeficiency in a Fell pony foal. J Vet Med A Physiol Pathol Clin Med — PubMed:PMID16466458 | DOI:10.1111/j.1439-0442.2006.00779.x — OMIA Phene_Article / Article - 2006. The Fell pony immunodeficiency syndrome also occurs in the Netherlands: a review and six cases. Tijdschr Diergeneeskd — PubMed:PMID16514970 — OMIA Phene_Article / Article - 2006. Fell Pony syndrome in a pony in North America. J Vet Intern Med — PubMed:PMID16496942 | DOI:10.1892/0891-6640(2006)20[198:fpsiap]2.0.co;2 — OMIA Phene_Article / Article - 2003. Aid to the antemortem diagnosis of Fell pony foal syndrome by the analysis of B lymphocytes. Vet Rec — PubMed:PMID12790165 | DOI:10.1136/vr.152.20.618 — OMIA Phene_Article / Article - 1998. A syndrome of anaemia, immunodeficiency and peripheral ganglionopathy in Fell pony foals. Vet Rec — PubMed:PMID9507645 — OMIA Phene_Article / Article - 2000. Discriminant and multiple regression analysis of anemia and opportunistic infection in Fell pony foals. Vet Clin Pathol — PubMed:PMID12070803 — OMIA Phene_Article / Article - 2009. Immunodeficiency/anaemia syndrome in a Dales pony. Vet Rec — PubMed:PMID19734561 — OMIA Phene_Article / Article - 2003. Immunodeficiency in Fell ponies. PhD Thesis, University of Liverpool — OMIA Phene_Article / Article - 2011. Identification of a mutation associated with fatal foal immunodeficiency syndrome in the fell and dales pony. PLoS Genet — PubMed:PMID21750681 | DOI:10.1371/journal.pgen.1002133 — OMIA Phene_Article / Article - 2011. Screening for foal immunodeficiency syndrome. Vet Rec — PubMed:PMID22184351 | DOI:10.1136/vr.d8118 — OMIA Phene_Article / Article - (1 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:600444 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [31]

English Spotted Pony, Australia (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: English Spotted Pony, Australia (Horse) [4]

Faeroes Pony (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Faeroes Pony (Horse) [18]

Fell Pony (Horse) — Foal immunodeficiency syndrome in Fell and Dales Pony; Fell pony syndrome (hereditary; OMIA-verified breed predisposition)

Breed: Fell Pony (Horse) [31]

Fjord (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Fjord (Horse) [18]

Freiberger (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Freiberger (Horse) [17]

Freiberger (Horse) — Congenital liver fibrosis (hereditary; OMIA-verified breed predisposition)

Disorder: Congenital liver fibrosis [32]

Summary: Hepatic fibrosis with cystic bile duct dilatation was observed in two- to twelve-months-old Franches-Montagnes foals. Affected foals commonly show pronounced hepatic encephalopathy with neurological disorders and laboratory findings of hepatic insufficiency. Livers in affected foals become severely enlarged and firm with multiple thin walled cysts. Their weight may be up to four fold higher than normal. Histologically, livers from affected foals show a diffuse portoportal bridging fibrosis with cystic bile ducts, forming a branching network. Affected foals die or are euthanized due to liver insufficiency. [32]

Clin feat: Affected foals will develop a liver failure, which can result in various clinical findings. Typical findings include fever and neurological symptoms resulting from the decreasing detoxification performance of the failing liver. An ultrasound examination will reveal an enlarged liver with cyst formation and clinical pathology will reveal grossly elevated liver enzymes. [32]

Pathology: The livers of affected foals are enlarged (up to 4-fold) and of a yellow-greyish color. Histologically, diffuse porto-portal bridging fibrosis with many small, irregularly formed and sometimes cystic bile ducts is seen. [32]

Prevalence: The carrier frequency of this recessive defect was estimated at 14% in 2011 (Leeb, unpublished data). Due to the systematic use of an indirect haplotype marker test in the breeding program, the frequency of the deleterious allele is decreasing and affected foals are hardly born any more (as of 2014). [32]

Gen test: The University of Bern offers an indirect marker test. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388956767 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: The 952 kb candidate region contains 10 annotated genes. Drögemüller et al. (2014) proposed the PKHD1 gene as plausible functional candidate gene as variants in this gene cause similar phenotypes in other species (human, mouse, rat). The PKHD1 gene encodes a protein, which had also been termed polyductin or fibrocystin (FCYT). In humans most PKHD1 mutations cause cyst formation in the kidney and l… Evidence (references) - 2014. Congenital hepatic fibrosis in the Franches-Montagnes horse is associated with the polycystic kidney and hepatic disease 1 (PKHD1) gene. PLoS One — PubMed:PMID25295861 | DOI:10.1371/journal.pone.0110125 — OMIA Phene_Article / Article - 2000. Congenital hepatic fibrosis and cystic bile duct formation in Swiss Freiberger horses. Vet Pathol — PubMed:PMID11105960 | DOI:10.1354/vp.37-6-669 — OMIA Phene_Article / Article - 2003. Intrahepatic bile duct cysts (Caroli's disease) with liver fibrosis in foals. A synopsis of signs and diagnosis of seven cases. (in German). Tierärztl Prax — OMIA Phene_Article / Article - 2018. Congenital hepatic fibrosis in a purebred Spanish horse foal: Pathology and genetic studies on PKHD1 gene mutations. Vet Pathol — PubMed:PMID29402207 | DOI:10.1177/0300985817754122 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:263200 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:606702 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [32]

Freiberger (Horse) — Hypertriglyceridemia-induced pancreatitis (hereditary; OMIA-verified breed predisposition)

Disorder: Hypertriglyceridemia-induced pancreatitis [33]

Clin feat: The main diagnostic feature of affected animals are severely elevated plasma triglyceride levels above 10 mmol/l compared to the reference range of 0.6-1 mmol/l for foals and 0.17-0.59 mmol/l for adult horses (Drögemüller et al. 2025). Drögemüller et al. (2025) reported 11 affected Franches-Montagnes horses: Ten of the 11 affected horses died or were euthanized between 6 days and 3 months of age due to severe pancreatitis. The most common clinical signs in affected foals included apathy, reluctance to nurse, abdominal distension and diarrhea, with fever observed in some cases. Other common clinicopathological abnormalities in foals included hypoproteinemia, azotemia, hyperbilirubinemia, hyperlipasemia, and elevated serum amyloid A concentrations.. One affected horse, a 13 year-old gelding, survived until adulthood and presented with a history of chronic weight loss, diarrhea, and intermittent fever, which had acutely worsened.. The horse was humanely euthanized after several days of treatment due to its lengthy medical history and compromised quality of life. [33]

Pathology: Drögemüller et al. (2025): Pathological examinations in eight affected foals revealed severe, acute to chronic necrotizing pancreatitis and extensive fibronecrotizing peritonitis. The affected adult horse was diagnosed with severe, multifocal, chronic active cholangiohepatitis and acute necrotizing hepatitis, mild chronic pancreatic fibrosis, and mild multifocal chronic peritoneal fibrosis. [33]

Prevalence: Drögemüller et al. (2025) reported a 15% carrier frequency for omia.variant:1823 in 2111 unaffected Franches-Montagnes horses at the time of variant discovery. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 398299034 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: The LMF1 gene encodes lipase maturation factor 1, a transmembrane protein in the endoplasmic reticulum required for the correct posttranslational maturation of the enzymes lipoprotein lipase (LPL) and hepatic lipase (HPL). Loss-of-function of LMF1 results in severe primary hypertriglyceridemia, which may trigger episodes of acute pancreatitis (Alves et al. 2024).Drögemüller e… Evidence (references) - 2025. LMF1 frameshift deletion in Franches-Montagnes horses with hypertriglyceridemia-induced pancreatitis. Sci Rep — PubMed:PMID40764662 | DOI:10.1038/s41598-025-13954-9 — OMIA Phene_Article / Article - 2024. Understanding Hypertriglyceridemia: Integrating Genetic Insights. Genes (Basel) — PubMed:PMID38397180 | DOI:10.3390/genes15020190 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:246650 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:611761 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [33]

French Trotter (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: French Trotter (Horse) [19]

Friesian (Horse) — Azoospermia (hereditary; OMIA-verified breed predisposition)

Breed: Friesian (Horse) [34]

Summary: Castaneda et al. (2021) report a detailed molecular cytogenetic analysis of a reciprocal translocation between horse (ECA) chromosomes Y and 13 in a Friesian stallion with complete meiotic arrest and azoospermia.. One resulting derivative chromosome, Y;13p, comprises of ECAY heterochromatin (ETSTY7 array), a small single copy and partial Y multicopy region, and ECA13p. Another derivative chromosome 13q;Y comprises of ECA13q and most of the single copy ECAY, the pseudoautosomal region and a small part of the Y multicopy region. A copy number (CN) analysis of select ECAY multicopy genes shows that the Friesian stallion has significantly (p 0.05) reduced CNs of TSPY, ETSTY1, and ETSTY5, suggesting that the translocation may not be completely balanced, and genetic material is lost. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2021. Molecular Cytogenetic and Y Copy Number Analysis of a Reciprocal ECAY-ECA13 Translocation in a Stallion with Complete Meiotic Arrest. Genes (Basel) — PubMed:PMID34946841 | DOI:10.3390/genes12121892 — OMIA Phene_Article / Article - 2021. Molecular Cytogenetic and Y Copy Number Analysis of a Reciprocal ECAY-ECA13 Translocation in a Stallion with Complete Meiotic Arrest. Genes (Basel) — PubMed:PMID34946841 | DOI:10.3390/genes12121892 — OMIA Phene_Article / Article [34]

Friesian (Horse) — Dwarfism, B4GALT7-related (hereditary; OMIA-verified breed predisposition)

Clin feat: As summarised by Orr et al. (2010), the Friesian dwarf phenotype results from physeal growth retardation in both limbs and ribs, reflected in a characteristic disproportional growth disturbance. The potential for post-natal growth in these animals, albeit at a reduced rate, is responsible for mature dwarfs having a head of the same size as unaffected animals, a broader chest with narrowing at the costochondral junction, a disproportionally long back and abnormally short limbs. Furthermore, radiographs reveal a dysplastic metaphysis of the distal metacarpus and metatarsus. Light microscopy of growth plates at the costochondral junction demonstrates an irregular transition from cartilage to bone, and thickening and disturbed formation of chondrocyte columns, which is similar to findings in osteochondrodysplasia. [35]

Prevalence: 177 Friesian horses were tested, with discovery of 22 carriers and 155 homozygotes for the reference allele. Not tested in other breeds. (Leegwater et al., 2016). (FN thanks Elizabeth Huffman, who substantially enhanced this section, working under the supervision of Professor Ernie Bailey; 23 April 2020) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388948310 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Whole genome sequencing was conducted on 4 dwarf Friesians and 3 non-affected Friesian controls, and the resultant sequences were compared in the candidate region with sequence from the horse reference genome and a Quarter Horse (a breed in which dwarfism has not been reported) (Leegwater et al., 2016). The authors identified a likely causal (missense) variant in Friesians as g.4535550C>T; c.50G>A… Evidence (references) - 2008. Phenotypic diagnosis of dwarfism in six Friesian horses. Equine Vet J — PubMed:PMID18267883 | DOI:10.2746/042516408X278201 — OMIA Phene_Article / Article - 2010. Genome-wide SNP association-based localization of a dwarfism gene in Friesian dwarf horses. Anim Genet — PubMed:PMID21070269 | DOI:10.1111/j.1365-2052.2010.02091.x — OMIA Phene_Article / Article - 2009. Normal function of the hypothalamic-pituitary growth axis in three dwarf Friesian foals. Vet Rec — PubMed:PMID19783851 | DOI:10.1136/vr.165.13.373 — OMIA Phene_Article / Article - 2000. Het Fokken van het Friese Paard [Breeding of the Friesian horse]. Schaafsma & Brouwer, Dokkum — OMIA Phene_Article / Article - 2016. Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7. BMC Genomics — PubMed:PMID27793082 | DOI:10.1186/s12864-016-3186-0 — OMIA Phene_Article / Article - 2021. Animal models of Ehlers-Danlos syndromes: Phenotype, pathogenesis, and translational potential. Front Genet — PubMed:PMID34712265 | DOI:10.3389/fgene.2021.726474 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2026. Pedigree-based assessment of genetic structure and disease-associated variants in Friesian horses in Brazil. J Equine Vet Sci — PubMed:PMID41865906 | DOI:10.1016/j.jevs.2026.105860 — OMIA Phene_Article / Article - 2026. Deficiency in homozygous haplotypes reveals recessive lethal variants affecting fertility and viability in the Friesian horse. BMC Genomics — PubMed:PMID41808016 | DOI:10.1186/s12864-026-12728-5 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:130070 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:604327 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [35]

German Riding Pony (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: German Riding Pony (Horse) [13]

Gotland Pony (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Gotland Pony (Horse) [18]

Haflinger (Horse) — Equine rhabdomyolysis syndrome; Polysaccharide storage myopathy; Tying-up (hereditary; OMIA-verified breed predisposition)

Breed: Haflinger (Horse) [8]

Holsteiner (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Holsteiner (Horse) [13]

Icelandic Horse (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Icelandic Horse (Horse) [22]

Icelandic Horse (Horse) — Coat colour, albinism, generic (hereditary; OMIA-verified breed predisposition)

Summary: See also: [OMIA:001821-9940]: Coat colour, albinism, oculocutaneous type IV in Ovis aries (sheep) for further detail on SLC45A2-related albinism in Suffolk sheep. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1988. [Morphological and histochemical features of the tissues of Karakul lambs with genetic albinism]. Sel'skokhozyaistvennaya Biologiya — OMIA Phene_Article / Article - 1988. [Inherited blood disorders in albinoid grey Karakul sheep] — OMIA Phene_Article / Article - 1993. Albinism in a Suffolk sheep. J Hered — PubMed:PMID8440890 | DOI:10.1093/oxfordjournals.jhered.a111279 — OMIA Phene_Article / Article - 1978. A note on an Icelandic albino ram. Journal of Heredity — OMIA Phene_Article / Article - 1977. Albinism in Icelandic sheep. J Hered — PubMed:PMID608941 | DOI:10.1093/oxfordjournals.jhered.a108857 — OMIA Phene_Article / Article - 1988. [Morphological and histochemical features of the tissues of Karakul lambs with genetic albinism]. Sel'skokhozyaistvennaya Biologiya — OMIA Phene_Article / Article - 1988. [Inherited blood disorders in albinoid grey Karakul sheep] — OMIA Phene_Article / Article - 1993. Albinism in a Suffolk sheep. J Hered — PubMed:PMID8440890 | DOI:10.1093/oxfordjournals.jhered.a111279 — OMIA Phene_Article / Article - 1978. A note on an Icelandic albino ram. Journal of Heredity — OMIA Phene_Article / Article - 1977. Albinism in Icelandic sheep. J Hered — PubMed:PMID608941 | DOI:10.1093/oxfordjournals.jhered.a108857 — OMIA Phene_Article / Article [36]

Icelandic Horse (Horse) — Equine Multiple Congenital Ocular Anomalies; previously known as Anterior Segment Dysgenesis or Congenital Aniridia (hereditary; OMIA-verified breed predisposition)

Disorder: Equine Multiple Congenital Ocular Anomalies; previously known as Anterior Segment Dysgenesis or Congenital Aniridia [37]

Mode of inheritance: Autosomal co-dominant [37]

Summary: This disorder is a pleiotropic effect of an allele/variant for Silver coat colour; see OMIA 001438-9796: Coat colour, silver in Equus caballus [37]

Clin feat: As summarised by Andersson et al. (2013), Horses with the MCOA phenotype are homozygous for the disease allele and have a wide range of eye anomalies.... These include, but are not restricted to, uveal cysts, cornea globosa, iris stromal hypoplasia, abnormal pectinate ligaments, cataracts and iris hypoplasia.... Horses that are heterozygous for the disease causing allele have the less severe Cyst phenotype which mainly consists of cysts that originate from the temporal ciliary body, iris, and/or extend into the temporal, peripheral retina Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: PMEL17 (Entrez Gene ID 4143454) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: From studying the exon 11 missense Silver mutation in PMEL17 (OMIA001438-9796) in five affected ponies, Komáromy et al. (2011) concluded "Our case series supports the notion that the (still unknown) MCOA [mutation] and the PMEL17 (Silver) [mutation] are the same, or at least overlap on ECA6q23". A month later, Andersson, Axelsson et al. (2011) confirmed the above result, by showing that in Iceland… Evidence (references) - 1996. Bilateral multiple congenital ocular defects in a standardbred foal [German]. Pferdeheilkunde — OMIA Phene_Article / Article - 2000. The horse homolog of congenital aniridia conforms to codominant inheritance. Journal of Heredity — PubMed:PMID10768120 — OMIA Phene_Article / Article - 2006. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genetics — PubMed:PMID17029645 | DOI:10.1186/1471-2156-7-46 — OMIA Phene_Article / Article - 2008. Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6. BMC Genet — PubMed:PMID19099555 | DOI:10.1186/1471-2156-9-88 — OMIA Phene_Article / Article - 2008. Congenital ocular anomalies in purebred and crossbred Rocky and Kentucky Mountain horses in Canada. Can Vet J — PubMed:PMID19412389 — OMIA Phene_Article / Article - 1999. Congenital ocular abnormalities of Rocky Mountain Horses. Vet Ophthalmol — PubMed:PMID11397242 — OMIA Phene_Article / Article - 2011. Targeted analysis of four breeds narrows equine Multiple Congenital Ocular Anomalies locus to 208 kilobases. Mamm Genome — PubMed:PMID21465164 | DOI:10.1007/s00335-011-9325-7 — OMIA Phene_Article / Article - 2011. Multiple Congenital Ocular Anomalies in Icelandic horses. BMC Vet Res — PubMed:PMID21615885 | DOI:10.1186/1746-6148-7-21 — OMIA Phene_Article / Article - 2011. Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome in PMEL17 (Silver) mutant ponies: five cases. Vet Ophthalmol — PubMed:PMID21929608 | DOI:10.1111/j.1463-5224.2011.00878.x — OMIA Phene_Article / Article - 2013. Ultrasonographic features of PMEL17 (Silver) mutant gene-associated multiple congenital ocular anomalies (MCOA) in Comtois and Rocky Mountain horses. Vet Ophthalmol — PubMed:PMID23278951 | DOI:10.1111/vop.12021 — OMIA Phene_Article / Article - 2013. Equine multiple congenital ocular anomalies and silver coat colour result from the pleiotropic effects of mutant PMEL. PLoS One — PubMed:PMID24086599 | DOI:10.1371/journal.pone.0075639 — OMIA Phene_Article / Article - 2017. Genetic testing as a tool to identify horses with or at risk for ocular disorders. Vet Clin North Am Equine Pract — PubMed:PMID29103563 | DOI:10.1016/j.cveq.2017.08.005 — OMIA Phene_Article / Article - (3 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:155550 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [37]

Japanese Draft, Japan (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Japanese Draft, Japan (Horse) [13]

Kentucky Mountain Saddle, United States of America (Horse) — Equine Multiple Congenital Ocular Anomalies; previously known as Anterior Segment Dysgenesis or Congenital Aniridia (hereditary; OMIA-verified breed predisposition)

Breed: Kentucky Mountain Saddle, United States of America (Horse) [37]

Knabstrupper (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: Knabstrupper (Horse) [4]

Lipizzan horse (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Lipizzan horse (Horse) [13]

Lusitanian (Horse) — Neuroaxonal dystrophy, generic (hereditary; OMIA-verified breed predisposition)

Breed: Lusitanian (Horse) [10]

Malopolski (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: Malopolski (Horse) [4]

Miniature Horse (Horse) — Dwarfism, ACAN-related (hereditary; OMIA-verified breed predisposition)

Breed: Miniature Horse (Horse) [38]

Prevalence: Eberth et al. (2018) reported the frequencies in Minatures of each variant were 0.03 for D1, 0.09 for D2, 0.02 for D3* and 0.03 for D4. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388932040 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Noting that the relevant region of chromosome ECA1 contains the ACAN gene that has been implicated in similar types of dwarfism in cattle (see OMIA 001271-9913) and humans (see OMIM entry above), Eberth (2013, Master's thesis) sequenced this comparative positional candidate gene in affected and normal Miniature horses, revealing four variants strongly associated with dwarfism: c.245del, p.K82fx in… Evidence (references) - 2014. Five things equine veterinarians should know about genomics. Equine Vet J — PubMed:PMID24909654 | DOI:10.1111/evj.12271 — OMIA Phene_Article / Article - 2013. Chondrodysplasia-Like Dwarfism in the Miniature Horse. Master's Thesis, University of Kentucky — OMIA Phene_Article / Article - 2017. Whole-genome sequencing reveals a potential causal mutation for dwarfism in the Miniature Shetland pony. Mamm Genome — PubMed:PMID27942904 | DOI:10.1007/s00335-016-9673-4 — OMIA Phene_Article / Article - 2009. Investigation of dwarfism Among Miniature Horses using the Illumina Horse SNP50 Bead Chip. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 2018. Multiple alleles of ACAN associated with chondrodysplastic dwarfism in Miniature horses. Anim Genet — PubMed:PMID30058072 | DOI:10.1111/age.12682 — OMIA Phene_Article / Article - 2020. Description of the D4/D4 genotype in Miniature horses with dwarfism. J Vet Diagn Invest — PubMed:PMID31906815 | DOI:10.1177/1040638719898164 — OMIA Phene_Article / Article - 2020. Evaluation of a new variant in the aggrecan gene potentially associated with chondrodysplastic dwarfism in Miniature horses. Sci Rep — PubMed:PMID32943661 | DOI:10.1038/s41598-020-72192-3 — OMIA Phene_Article / Article - 2020. Heterozygotes for ACAN dwarfism alleles in horses have reduced stature. Anim Genet — PubMed:PMID32065671 | DOI:10.1111/age.12921 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Genetic factors underlying mandibular prognathism: insights from recent human and animal studies. Mamm Genome — PubMed:PMID39607497 | DOI:10.1007/s00335-024-10084-x — OMIA Phene_Article / Article - 2023. Molecular Genetic Studies of Horses, Especially With Reference to Aggrecan and Dwarfism. PhD Thesis, University of Kentucky — DOI:10.13023/etd.2023.276 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:612813 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:165800 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:608361 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:155760 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [38]

Missouri Fox Trotter, Germany (Horse) — Equine Multiple Congenital Ocular Anomalies; previously known as Anterior Segment Dysgenesis or Congenital Aniridia (hereditary; OMIA-verified breed predisposition)

Breed: Missouri Fox Trotter, Germany (Horse) [37]

Missouri Fox Trotting Horse (Horse) — Curly coat (hereditary; OMIA-verified breed predisposition)

Breed: Missouri Fox Trotting Horse (Horse) [7]

Missouri Fox Trotting Horse, United States of America (Horse) — Night blindness, congenital stationary, GRM6-related (hereditary; OMIA-verified breed predisposition)

Breed: Missouri Fox Trotting Horse, United States of America (Horse) [16]

Mongolian (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Mongolian (Horse) [18]

Morgan (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Morgan (Horse) [17]

New Forest Pony (Horse) — Myotonia (hereditary; OMIA-verified breed predisposition)

Breed: New Forest Pony (Horse) [39]

Summary: As summarised by Valberg (2014), Myotonic muscle disorders share the feature of delayed relaxation of muscle after mechanical stimulation or voluntary contraction due to abnormal muscle membrane conduction. Horses have three known forms of myotonia: myotonia congenita, myotonia dystrophica, and hyperkalemic periodic paralysis (HyPP). This OMIA entry deals with Myotonia congentia. (FN thanks Izabela De Assis Rocha, who provided the basis of this contribution, working under the supervision of Professor Ernie Bailey; 15 April 2020) [39]

Clin feat: From the case report described in a New Forest Pony by Wijnberg et al. (2012), the main clinical signs of myotonia congenita are the recurrent episodes of recumbency and difficulty to rise due to muscle stiffness. Occasionally, when the horse is stimulated, it seemed hyperreactive and temporary protrusion of the third eyelid occurred due to retraction of the eye uni- or bilaterally. It is important to note that this case report included only one affected foal. (FN thanks Izabela De Assis Rocha, who provided the basis of this contribution, working under the supervision of Professor Ernie Bailey; 15 April 2020) [39]

Prevalence: The occurrence of this variant in a wider sample of 42 additional New Forest ponies and 56 horses from 13 other breeds was consistent with it being causal of an autosomal recessive disorder in the New Forest breed: from the total 102 horses included in this study, Wijnberg et al (2012) found that the affected foal was the only homozygous C/C for the mutated allele 1775C, whereas its sire, its dam and seven other mares related to the foal were heterozygous A/C. All other horses here homozygous A/A for the wildtype allele 1775A. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 166568129 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: A gene defect in CLCN1 was then known to cause similar phenotypes in humans (see OMIM links above) and in goats (OMIA 000698-9925 and in dogs (OMIA 000698-9615), which led Wijnberg et al (2012) to adopt a comparative candidate gene approach. By sequencing "all exons and several introns of the equine C… Evidence (references) - 1962. Myotonia in a horse. Science — PubMed:PMID13916691 — OMIA Phene_Article / Article - 1987. A congenital form of myotonia with dystrophic changes in a quarterhorse. Equine Vet J — PubMed:PMID3622468 — OMIA Phene_Article / Article - 1988. Progressive myotonia in foals resembling human dystrophia myotonica. Muscle Nerve — PubMed:PMID3398875 | DOI:10.1002/mus.880110403 — OMIA Phene_Article / Article - 2012. A missense mutation in the skeletal muscle chloride channel 1 (CLCN1) as candidate causal mutation for congenital myotonia in a New Forest pony. Neuromuscul Disord — PubMed:PMID22197188 | DOI:10.1016/j.nmd.2011.10.001 — OMIA Phene_Article / Article - 1987. Myotonia in man and animals: confusing comparisons. Equine Vet J — PubMed:PMID3622451 | DOI:10.1111/j.2042-3306.1987.tb01401.x — OMIA Phene_Article / Article - 2014. Myotonic Disorders in Horses. MSD (Veterinary) Manual [https://www.msdvetmanual.com/musculoskeletal-system/myopathies-in-horses/myotonic-disorders-in-horses] — OMIA Phene_Article / Article - 2022. Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci — PubMed:PMID36150530 | DOI:10.1016/j.jevs.2022.104129 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:160800 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:255700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:118425 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [39]

Noric (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: Noric (Horse) [4]

Noric (Horse) — Coat colour, roan (hereditary; OMIA-verified breed predisposition)

Prevalence: Grizl-Seger et al. (2020): The G -allele of the top associated SNP was present in other roan horses, namely Quarter Horse, Murgese, Slovenian, and Belgian draught horse, while it was absent in a panel of 15 breeds, including 657 non-roan horses. In further 379 gray Lipizzan horses, eight animals exhibited a heterozygous genotype (A/G). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: c-kit (Entrez Gene ID 5430480) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Building on the results of work showing that dominant white coat colour in pigs is due to a mutation at the KIT gene (see OMIA 000209), Marklund (1997) reported very strong evidence that the KIT gene in horses is the gene for roan coat colour: a linkage study revealed zero recombinantion between Roan and KIT, and a 79 bp insertion between exons 1 and 2 of the KIT gene, creating a frameshift mutati… Evidence (references) - 1982. A linkage group composed of 3 coat colour genes and 3 serum protein loci in horses. Journal of Heredity — PubMed:PMID7096983 — OMIA Phene_Article / Article - 1994. Parentage Testing and Linkage Analysis in the Horse Using a Set of Highly Polymorphic Microsatellites. Animal Genetics — PubMed:PMID8161016 — OMIA Phene_Article / Article - 1999. Close association between sequence polymorphism in the KIT gene and the roan coat color in horses. Mammalian Genome — PubMed:PMID10051325 — OMIA Phene_Article / Article - 2009. Molecular tests for coat colours in horses. J Anim Breed Genet — PubMed:PMID19912415 | DOI:10.1111/j.1439-0388.2009.00832.x — OMIA Phene_Article / Article - 1984. Direct evidence for linkage of roan and extension loci in Belgian horses. J Hered — PubMed:PMID6481131 — OMIA Phene_Article / Article - 1979. Lethal dominant roan in horses. Journal of Heredity — OMIA Phene_Article / Article - 2017. Equine Color Genetics, 4th Edition. Wiley-Blackwell, Hoboken, NJ — OMIA Phene_Article / Article - 2020. A genome-wide association analysis in Noriker horses identifies a SNP associated with roan coat color. J Equine Vet Sci — PubMed:PMID32303326 | DOI:10.1016/j.jevs.2020.102950 — OMIA Phene_Article / Article - 2020. Coat Color Roan Shows Association with KIT Variants and No Evidence of Lethality in Icelandic Horses. Genes (Basel) — PubMed:PMID32580410 | DOI:10.3390/genes11060680 — OMIA Phene_Article / Article - 2022. Roan coat color in livestock. Anim Genet — PubMed:PMID35811453 | DOI:10.1111/age.13240 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Spotting the pattern: A review on white coat color in the domestic horse. Animals (Basel) — PubMed:PMID38338094 | DOI:10.3390/ani14030451 — OMIA Phene_Article / Article - (2 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:184745 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:611664 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [40]

Oldenburg (Horse) — Thrombasthenia (hereditary; OMIA-verified breed predisposition)

Breed: Oldenburg (Horse) [41]

Prevalence: Leite et al. (2020) reported that the two known likely causal variants were completely absent from 1053 DNA samples of clinically healthy Quarter Horse (n = 679) and Warmblood horses (n = 374) in Brazil, consistent with the observation that this disease has not been described in Brazil. Although their samples were of adequate size, the authors rightly concluded that it is not possible to affirm that there are no horses carrying mutated alleles in Brazil. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4119385 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 2007. A 10-base-pair deletion in the gene encoding platelet glycoprotein IIb associated with Glanzmann thrombasthenia in a horse. J Vet Intern Med — PubMed:PMID17338169 — OMIA Phene_Article / Article - 2006. Characterization of the cDNA Encoding alphaIIb and beta3 in normal horses and two horses with Glanzmann thrombasthenia. Vet Pathol — PubMed:PMID16407493 | DOI:10.1354/vp.43-1-78 — OMIA Phene_Article / Article - 2005. Platelet dysfunction (Glanzmann's thrombasthenia) in horses. J Vet Intern Med — PubMed:PMID16355691 — OMIA Phene_Article / Article - 2007. Glanzmann thrombasthenia in an Oldenbourg filly. Vet Clin Pathol — PubMed:PMID17523098 — OMIA Phene_Article / Article - 2011. Glanzmann thrombasthenia in a 17-year-old Peruvian Paso mare. Vet Clin Pathol — PubMed:PMID21291483 | DOI:10.1111/j.1939-165X.2011.00289.x — OMIA Phene_Article / Article - 2019. Prevalence of the Mutations Responsible for Glanzmann Thrombasthenia in Horses in Brazil. Animals (Basel) — PubMed:PMID31766112 | DOI:10.3390/ani9110960 — OMIA Phene_Article / Article - 2021. Genetics of equine bleeding disorders. Equine Vet J — PubMed:PMID32463964 | DOI:10.1111/evj.13290 — OMIA Phene_Article / Article - 2011. Characterization of the cDNA and genomic DNA sequence encoding for the platelet integrin alpha IIB and beta III in a horse with Glanzmann thrombasthenia. Can J Vet Res — PubMed:PMID22210999 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:273800 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:607759 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [41]

Paso Fino (Horse) — Curly coat (hereditary; OMIA-verified breed predisposition)

Breed: Paso Fino (Horse) [7]

Paso Fino (Horse) — Tiger-eye or Goat-eye (hereditary; OMIA-verified breed predisposition)

Disorder: Tiger-eye or Goat-eye [42]

Summary: Mack et al. (2017): A unique eye color, called tiger-eye, segregates in the Puerto Rican Paso Fino (PRPF) horse breed and is characterized by a bright yellow, amber, or orange iris. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388946352 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Mack et al. (2017): "Twenty tiger-eye horses were homozygous for a nonsynonymous mutation in exon 2 (p.Phe91Tyr) of SLC24A5 (called here Tiger-eye 1), which is predicted to be deleterious to protein function. Additionally, eight of the remaining 12 tiger-eye horses heterozygous for the p.Phe91Tyr variant were also heterozygous for a 628 bp deletion encompassing all of exon 7 of SLC24A5 (c.875-340_… Evidence (references) - 2012. A genome-wide association study identifies “tiger” eye color variation locus on ECA1 in Puerto Rican Paso Fino horses. Proceedings of the 33rd Conference of the International Society of Animal Genetics — OMIA Phene_Article / Article - 2017. Two variants in SLC24A5 are associated with "Tiger-Eye" iris pigmentation in Puerto Rican Paso Fino horses. G3 (Bethesda) — PubMed:PMID28655738 | DOI:10.1534/g3.117.043786 — OMIA Phene_Article / Article - 2011. Investigation of HERC2 and OCA2 SNP for iris color variation in puerto rican paso fino horses. Journal of Equine Veterinary Science — DOI:10.1016/j.jevs.2011.03.154 — OMIA Phene_Article / Article - 2010. A mutation in the equine SLC24A5 gene is associated with a dilution of black horses. Proceedings of the 9th World Congress on Genetics Applied to Livestock Production Leipzig (Germany). August 1-6. — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:113750 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:609802 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [42]

Percheron (Horse) — Curly coat (hereditary; OMIA-verified breed predisposition)

Breed: Percheron (Horse) [7]

Peruvian Paso (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Peruvian Paso (Horse) [19]

Peruvian Paso (Horse) — inherited myoclonus (hereditary; OMIA-verified breed predisposition)

Disorder: inherited myoclonus [43]

Summary: Gundlach et al. (1993) report the occurrence of. [a] stimulus-induced myoclonus in individual, pure-bred Peruvian Paso horses and an associated, specific deficiency in the density of [3H]strychnine binding to inhibitory glycine receptors sites in spinal cord of these animals. The authors suggest that the disease is similar to inherited myoclonus in Poll Hereford calves (see OMIA:000689-9913: Hyperekplexia, GLRA1-related in Bos taurus). However, the underlying molecular genetic cause in horses has not been identified, and the disease in horses and may not be associated with variants in the GLRA1 gene. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1993. Deficit of inhibitory glycine receptors in spinal cord from Peruvian Pasos - Evidence for an equine form of inherited myoclonus. Brain Res — PubMed:PMID8313155 | DOI:10.1016/0006-8993(93)90963-n — OMIA Phene_Article / Article - 1993. Deficit of inhibitory glycine receptors in spinal cord from Peruvian Pasos - Evidence for an equine form of inherited myoclonus. Brain Res — PubMed:PMID8313155 | DOI:10.1016/0006-8993(93)90963-n — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:149400 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:138491 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:149400 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:138491 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [43]

Polish Konik (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Polish Konik (Horse) [18]

Pony (Horse) — Familial adenomatous polyposis (hereditary; OMIA-verified breed predisposition)

Breed: Pony (Horse) [44]

Mode of inheritance: Probably autosomal dominant [44]

Clin feat: Martin et al. (2026) report a 12 year-old-pony mare with bilateral nasal discharge, cutaneous masses, and numerous hard enlargements involving the bones of the skull, maxilla, mandible, and cervical vertebrae. Oral exam revealed advanced dental disease with hard enlargements adjacent to and between numerous cheek teeth. Radiographs and computed tomography confirmed the presence of severe dental disease and proliferative bone lesions disseminated along the skull, hyoid apparatus, and cranial cervical vertebrae. The bony proliferations extended into the subcutis, nasal cavity, paranasal sinuses, orbits, cranial vault, and vertebral canal. [44]

Pathology: Martin et al. (2026): On necropsy, multiple osteomas were present on the skull and to a lesser extent the cervical vertebrae. Additional abnormalities included multiple mucosal polyps in the small intestine, epidermal inclusion cysts, and adrenocortical adenomas. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 398299103 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Martin et al. (2026): "Whole genome sequencing and variant discovery in the [affected] pony identified multiple unique variants, including a likely pathogenic single base pair insertion leading to a frameshift in APC (ENSECAP00000007276.1:p.Glu1527ArgfsTer9) [omia.variant:1897]." Evidence (references) - 2026. Germline pathogenic variant in the APC gene suggestive of Gardner syndrome in a pony. Case Rep Vet Med — PubMed:PMID42038751 | DOI:10.1155/crve/1395580 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:175100 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:611731 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [44]

Pony Of the Americas, Germany (Horse) — Coat colour, Leopard Complex Spotting (hereditary; OMIA-verified breed predisposition)

Breed: Pony Of the Americas, Germany (Horse) [4]

Purebred Spanish (Horse) — Congenital liver fibrosis (hereditary; OMIA-verified breed predisposition)

Breed: Purebred Spanish (Horse) [32]

Purebred Spanish (Horse) — also known as Swan Neck, Turkey Neck, and Upside-down Neck (hereditary; OMIA-verified breed predisposition)

Disorder: also known as Swan Neck, Turkey Neck, and Upside-down Neck [45]

Summary: Ripolles et al.:2020): Ewe Neck is one of the disqualifying morphological defects in PRE [Pura Raza Español] horses. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2020. Survey of risk factors and genetic characterization of ewe neck in a world population of Pura Raza Español horses. Animals (Basel) — PubMed:PMID33019702 | DOI:10.3390/ani10101789 — OMIA Phene_Article / Article - 2025. Genetic relationship between Neck and Limb defects in Pura Raza Española Horses. J Equine Vet Sci — PubMed:PMID40505788 | DOI:10.1016/j.jevs.2025.105630 — OMIA Phene_Article / Article - 2020. Survey of risk factors and genetic characterization of ewe neck in a world population of Pura Raza Español horses. Animals (Basel) — PubMed:PMID33019702 | DOI:10.3390/ani10101789 — OMIA Phene_Article / Article - 2025. Genetic relationship between Neck and Limb defects in Pura Raza Española Horses. J Equine Vet Sci — PubMed:PMID40505788 | DOI:10.1016/j.jevs.2025.105630 — OMIA Phene_Article / Article [45]

Quarter Horse (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Quarter Horse (Horse) [22]

Quarter Horse (Horse) — Equine Juvenile Spinocerebellar Ataxia; EJSCA (hereditary; OMIA-verified breed predisposition)

Disorder: Equine Juvenile Spinocerebellar Ataxia; EJSCA [46]

Summary: Willis et al. (2024) report a novel lethal spinocerebellar ataxia in 12 related young Quarter Horses that is etiologically distinct from other clinically similar neurological disorders. [46]

Clin feat: Brown et al. (2026): Affected [Quarter Horse] foals [appear healthy at birth and] display a progressive proprioceptive ataxia by 1–5 weeks of age, leading to recumbency and necessitating euthanasia.. Clinicopathologic findings included elevated gamma-glutamyl transferase (GGT) and hyperglycemia on biochemical profiles, with normal muscle enzymes. [46]

Pathology: Brown et al. (2026): Postmortem evaluation identified dilated myelin sheaths with digestion chambers throughout the entire spinal cord but most severe in the dorsal spinocerebellar tracts of the cervicothoracic region. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 398299091 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Brown et al. (2025) reported in a conference abstract reduced FDXR expression in horses with equine juvenile spinocerebellar ataxia and propose that an intronic G>C SNP in intron 2 of FDXR is the likely causal variant (omia.variant:1914). The variant introduces a new splice site, resulting in a cryptic exon which is predicted to result in nonsense-mediated mRNA decay. De… Evidence (references) - 2024. Clinicopathological and pedigree investigation of a novel spinocerebellar neurological disease in juvenile Quarter Horses in North America. J Vet Intern Med — PubMed:PMID38669583 | DOI:10.1111/jvim.17049 — OMIA Phene_Article / Article - 2025. Identification of a cryptic exon in FDXR associated with equine juvenile spinocerebellar ataxia in Quarter Horses. Journal of Equine Veterinary Science — DOI:10.1016/j.jevs.2025.105561 — OMIA Phene_Article / Article - 2026. An intronic variant in ferredoxin reductase (FDXR) creates a cryptic exon in Quarter Horses with equine juvenile spinocerebellar ataxia. PLoS Genet — PubMed:PMID42160398 | DOI:10.1371/journal.pgen.1012158 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:103270 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:620887 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [46]

Quarter Horse (Horse) — Fanconi syndrome (hereditary; OMIA-verified breed predisposition)

Summary: Ohmes et al. (2014) report two cases of acquired Fanconi syndrome in horses. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2014. Transient Fanconi syndrome in Quarter horses. Can Vet J — PubMed:PMID24489393 — OMIA Phene_Article / Article - 2014. Transient Fanconi syndrome in Quarter horses. Can Vet J — PubMed:PMID24489393 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:227810 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:138160 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:227810 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:138160 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [47]

Quarter Horse (Horse) — Hyperkalemic Periodic Paralysis (HYPP) (hereditary; OMIA-verified breed predisposition)

Disorder: Hyperkalemic Periodic Paralysis (HYPP) [48]

Summary: HYPP in horses is an autosomal incompletely dominant disorder characterized by episodic attacks of muscle tremors, weakness and paralysis with associated increased serum potassium concentration (Rudolph et al., 1992; Animal Genetics). While HYPP is considered a defect by the American Quarter Horse Association (AQHA), some breeders consider the muscular phenotype attractive and select for this phenotype. Thus, the AQHA refuses to register homozygous animals, but still registers heterozygotes. {with thanks to Tatyana German and Meredith O’Connell, working under the guidance of Professor Ernie Bailey; 15 Feb 2019} [48]

Clin feat: Muscle fasciculation and spasm; weakness; recumbency; episodic attacks of muscle tremors, weakness and paralysis with associated increased serum potassium concentration; pronounced muscularity; attacks follow diet changes, fasting, stressful circumstances or after consumption of alfalfa hay which is high in potassium (Steiss & Naylor 1986; Spier et al., 1990) {with thanks to Tatyana German and Meredith O’Connell, working under the guidance of Professor Ernie Bailey; 15 Feb 2019} [48]

Prevalence: Quarter Horse; Bowling et al. (1996) reported that all horses possessing the variant were descendants of a “Stallion 1” subsequently identified as IMPRESSIVE, born in 1969. Tryon et al.( 2009) tested subpopulations of Quarter Horses and found the variant absent among cutting horses, cow horses, reining horses and racing horses. It was present among barrel racing horses (allele frequency 0.006), western pleasure horses (allele frequency 0.013) and halter horses (allele frequency 0.299). The variant was also found among paint horses that were crosses from Quarter Horse. {with thanks to Tatyana German and Meredith O’Connell, working under the guidance of Professor Ernie Bailey; 15 Feb 2019} Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4153124 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: The molecular basis of this disorder was first reported by Rudolph et al. (1992, Nature Genetics). Having established that the horse gene for adult skeletal muscle sodium channel (SNC4A) is completely linked with this disorder (see Mapping section above), Rudolph et al. (1992, Nature Genetics) identified the causative mutation as a missense mutation causing an amino acid substitution from phenylal… Evidence (references) - 1992. Linkage of Hyperkalaemic Periodic Paralysis in Quarter Horses to the Horse Adult Skeletal Muscle Sodium Channel Gene. Animal Genetics — PubMed:PMID1323940 — OMIA Phene_Article / Article - 1992. Inheritance of Myotonic Discharges in American Quarter Horses and the Relationship to Hyperkalemic Periodic Paralysis. Canadian Journal of Veterinary Research - Revue Canadienne de Recherche Veterinaire — PubMed:PMID1586896 — OMIA Phene_Article / Article - 1992. Familial Incidence of Hyperkalemic Periodic Paralysis in Quarter Horses. Journal of the American Veterinary Medical Association — PubMed:PMID1548168 — OMIA Phene_Article / Article - 1992. Periodic Paralysis in Quarter Horses - A Sodium Channel Mutation Disseminated by Selective Breeding. Nature Genetics — PubMed:PMID1338908 | DOI:10.1038/ng1092-144 — OMIA Phene_Article / Article - 1993. Genetic Study of Hyperkalemic Periodic Paralysis in Horses. Journal of the American Veterinary Medical Association — PubMed:PMID8468218 — OMIA Phene_Article / Article - 1993. Clinical Syndrome and Diagnosis of Hyperkalaemic Periodic Paralysis in Quarter Horses. Equine Veterinary Journal — PubMed:PMID8508753 — OMIA Phene_Article / Article - 1993. Blood Test Available for Hyperkalemic Periodic Paralysis in Quarter Horses. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 1993. Hyperkalaemic Periodic Paralysis - Diagnosing the Disease in the Headlines. Equine Veterinary Journal — PubMed:PMID8508741 — OMIA Phene_Article / Article - 1993. Phenytoin Increases Specific Triacylglycerol Fatty Esters in Skeletal Muscle from Horses with Hyperkalemic Periodic Paralysis. Biochimica et Biophysica Acta — PubMed:PMID8323969 — OMIA Phene_Article / Article - 1994. Selection of Quarter Horses Affected with Hyperkalemic Periodic Paralysis by Show Judges. Journal of the American Veterinary Medical Association — PubMed:PMID8188514 — OMIA Phene_Article / Article - 1994. Equine Hyperkalemic Periodic Paralysis - Review and Implications. Canadian Veterinary Journal - Revue Veterinaire Canadienne — OMIA Phene_Article / Article - 1994. Hyperkalemic Periodic Paralysis in Horses .2. Magyar Allatorvosok Lapja — OMIA Phene_Article / Article - (36 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:170500 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:603967 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:613345 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:614198 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:608390 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:168300 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [48]

Quarter Horse (Horse) — Incontinentia pigmenti (hereditary; OMIA-verified breed predisposition)

Disorder: Incontinentia pigmenti [49]

Mode of inheritance: X-linked incomplete dominant [49]

Summary: Incontinentia pigmenti (IP) is an ectodermal dysplasia characterized by skin lesions evolving over time, as well as dental, nail, and ocular abnormalities. Due to X-linked dominant inheritance IP symptoms can only be seen in female individuals while affected males die during development in utero. [49]

Clin feat: Affected mares develop pruritic, exudative lesions soon after birth. These evolve into wart-like lesions and areas of alopecia. Occasionally, hair re-growth with a wooly appearance is observed. Affected horses also have streaks of darker and lighter coat coloration from birth resembling the brindled coat color. The cutaneous manifestations follow the lines of Blaschko. Other clinical symptoms include anomalies of tooth, hoof and ocular development (Towers et al. 2013). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388948485 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: After having established the X-chromosomal inheritance the genome of an affected crossbred mare was re-sequenced at 19x coverage (Towers et al. 2013). The analysis of the sequence data yielded 557 non-synonymous variants on the X-chromosome with respect to the genome reference sequence of an unaffected Thoroughbred mare. Exclusion of variants that were also present in the genome sequences of 44 co… Evidence (references) - 2013. A nonsense mutation in the IKBKG gene in mares with incontinentia pigmenti. PLoS One — PubMed:PMID24324710 | DOI:10.1371/journal.pone.0081625 — OMIA Phene_Article / Article - 2000. Genomic rearrangement in NEMO impairs NF-kappaB activation and is a cause of incontinentia pigmenti. The International Incontinentia Pigmenti (IP) Consortium. Nature — PubMed:PMID10839543 | DOI:10.1038/35013114 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:308300 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:300248 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [49]

Racking Horse (Horse) — Night blindness, congenital stationary, GRM6-related (hereditary; OMIA-verified breed predisposition)

Breed: Racking Horse (Horse) [16]

Rocky Mountain Horse (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Rocky Mountain Horse (Horse) [19]

Rocky Mountain, United States of America (Horse) — Equine Multiple Congenital Ocular Anomalies; previously known as Anterior Segment Dysgenesis or Congenital Aniridia (hereditary; OMIA-verified breed predisposition)

Breed: Rocky Mountain, United States of America (Horse) [37]

Scandinavian Coldblood Trotter (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Scandinavian Coldblood Trotter (Horse) [19]

Shetland Pony (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Shetland Pony (Horse) [17]

Shetland Pony (Horse) — Coat colour, phaeomelanin dilution, MFSD12-related (hereditary; OMIA-verified breed predisposition)

Summary: Tanaka et al. (2019): Mushroom is a unique coat color phenotype in Shetland Ponies characterized by the dilution of the chestnut coat color to a sepia tone. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 398298778 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Tanaka et al. (2019) provided evidence supporting a frameshift mutation (p.Asp201fs) in the MFSD12 gene as being a likely causal variant for the mushroom coat colour: "This variant was perfectly concordant with phenotype in 96 Shetland Ponies (P = 1.15 × 10-22), was identified in the closely related Miniature Horse for which the mushroom phenotype is suspected to occur (fmu = 0.02), and was absent… Evidence (references) - 2019. A frameshift variant in MFSD12 explains the mushroom coat Color dilution in Shetland Ponies. PAG XXVII — OMIA Phene_Article / Article - 2019. Frameshift variant in MFSD12 explains the mushroom coat color dilution in Shetland Ponies. Genes (Basel) — PubMed:PMID31635058 | DOI:10.3390/genes10100826 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:617745 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [50]

Shetland Pony (Horse) — Skeletal atavism (hereditary; OMIA-verified breed predisposition)

Mode of inheritance: Recessive [51]

Clin feat: As reported by Rafati et al. (2016), Skeletal atavism in Shetland ponies is a heritable disorder characterized by abnormal growth of the ulna and fibula that extend the carpal and tarsal joints, respectively. This causes abnormal skeletal structure, impaired movements, and affected foals are usually euthanized. [51]

Prevalence: When testing a random set of 94 Shetland ponies in Sweden, the allele frequencies of disease associated deletions Del1 and Del2 were 0.0479 and 0.0106, respectively (Rafati et al., 2016) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 389001865 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: The deletions mentioned in the Mapping section were named Del-1 and Del-2 (Rafati et al., 2016), and the authors reported that "One of the identified deletions removes the entire coding region of the short stature homeobox (SHOX) gene [Del-1] and both deletions remove parts of the cytokine receptor-like factor 2 (CRLF2) gene located downstream of SHOX." The same authors then "sequenced bacterial a… Evidence (references) - 1958. A cause of malformation of the limbs of Shetland ponies with a note on its phylogenic significance. British Veterinary Journal — OMIA Phene_Article / Article - 1995. Limb deviation in a Shetland pony foal. Equine Practice — OMIA Phene_Article / Article - 2004. Skeletal atavism in a miniature horse. Vet Radiol Ultrasound — PubMed:PMID15373256 | DOI:10.1111/j.1740-8261.2004.04060.x — OMIA Phene_Article / Article - 1970. A hereditary anomaly in Shetland ponies. Netherlands Journal of Veterinary Science — OMIA Phene_Article / Article - 1987. Investigation into the heredity of congenital lateral patellar (sub)luxation in the Shetland pony. Vet Q — PubMed:PMID3564314 | DOI:10.1080/01652176.1987.9694070 — OMIA Phene_Article / Article - 1995. Atavisms and atavistic mutations. Nat Genet — PubMed:PMID7663504 | DOI:10.1038/ng0695-126 — OMIA Phene_Article / Article - 2016. Large deletions at the SHOX locus in the pseudoautosomal region are associated with skeletal atavism in Shetland ponies. G3 (Bethesda) — PubMed:PMID27207956 | DOI:10.1534/g3.116.029645 — OMIA Phene_Article / Article - 1985. Complete ulnas and fibulas in a pony foal. J Am Vet Med Assoc — PubMed:PMID3997641 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:312865 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:249700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:127300 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:300582 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [51]

Spiti Pony, India (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Spiti Pony, India (Horse) [19]

Spotted Saddle Horse (Horse) — Night blindness, congenital stationary, GRM6-related (hereditary; OMIA-verified breed predisposition)

Breed: Spotted Saddle Horse (Horse) [16]

Standardbred x Tennessee Walking Horse cross (Horse) — Palomino (hereditary; OMIA-verified breed predisposition)

Breed: Standardbred x Tennessee Walking Horse cross (Horse) [12]

Swedish Warmblood (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Swedish Warmblood (Horse) [18]

Süddeutsches Kaltblut, Germany (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Süddeutsches Kaltblut, Germany (Horse) [13]

Tennessee Walking Horse (Horse) — Curly coat (hereditary; OMIA-verified breed predisposition)

Breed: Tennessee Walking Horse (Horse) [7]

Thoroughbred (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Thoroughbred (Horse) [17]

Thoroughbred (Horse) — Hypoparathyroidism, RAPGEF5-related (hereditary; OMIA-verified breed predisposition)

Clin feat: Beyer et al. (1997): “Five thoroughbred foals (4 fillies and 1 colt), all in good to excellent body condition, ranging in age from 4 days to 5 weeks at the time of onset of signs, were presented …. All 5 foals presented with tachycardia, hyperhidrosis, diarrhea or a recent history of diarrhea, and muscle rigidity or stiff gait. Four of the 5 foals presented for recumbency, seizure-like activity with opisthotonos, or pronounced extensor muscle rigidity. All 5 foals were hypocalcemic. All foals either died or had euthanasia performed.” The foals investigated by Rivas et al. (2020) presented with fatal idiopathic hypocalcemia, tetany and seizures. [52]

Pathology: In four of the 5 foals reported by Beyer et al. (1997) necropsy examination were conducted and in all 4 foals parathyroid tissue could not be identified. In the cases reported by Rivas et al. (2020) the only consistent gross or histologic lesions present across all cases was the absence of normal parathyroid glands. [52]

Prevalence: Elcombe et al. (2023) reported the c.2624C>A variant (OMIA variant 1369) at a frequency of less than 1% in the US Thoroughbred population (1988-2019). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388955687 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Rivas et al. (2020): "We performed whole-genome sequencing of the two foals, their unaffected dams and four unaffected, unrelated TB horses. Both homozygosity mapping and an association analysis were used to prioritize potential genetic variants. Of the 2,808 variants that significantly associated with the phenotype using an AR mode of inheritance (P<0.02) and located within a region of homozyg… Evidence (references) - 2020. A nonsense variant in Rap Guanine Nucleotide Exchange Factor 5 (RAPGEF5) is associated with equine familial isolated hypoparathyroidism in Thoroughbred foals. PLoS Genet — PubMed:PMID32986719 | DOI:10.1371/journal.pgen.1009028 — OMIA Phene_Article / Article - 1997. Idiopathic hypocalcemia in foals. J Vet Intern Med — PubMed:PMID9470161 | DOI:10.1111/j.1939-1676.1997.tb00480.x — OMIA Phene_Article / Article - 2023. Prevalence of the RAPGEF5 c.2624C>A and PLOD1 c.2032G>A variants associated with equine familial isolated hypoparathyroidism and fragile foal syndrome in the US Thoroughbred population (1988-2019). Equine Vet J — PubMed:PMID36199159 | DOI:10.1111/evj.13883 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:609527 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [52]

Thoroughbred (Horse) — kyphoscoliotic Ehlers-Danlos syndrome (kEDS), PLOD1-related; Fragile Foal Syndrome; Fragile Foal Syndrome Type 1; Warmblood Fragile Foal Syndrome (hereditary; OMIA-verified breed predisposition)

Disorder: kyphoscoliotic Ehlers-Danlos syndrome (kEDS), PLOD1-related; Fragile Foal Syndrome; Fragile Foal Syndrome Type 1; Warmblood Fragile Foal Syndrome [53]

Summary: Originally this disorder was called Warmblood Fragile Foal Syndrome (WBFFS or WFFS), but with the discovery of the disorder in other breeds, the breed name has since been dropped and called Fragile Foal Syndrome. This phene has been renamed from Ehlers-Danlos Syndrome, type VI (Fragile Foal Syndrome) to kyphoscoliotic Ehlers-Danlos syndrome (kEDS), PLOD1-related in OMIA on the basis of the review on human Ehlers-Danlos syndromes by Malfait et al. (2020) [2/6/2022]. [53]

Clin feat: A Warmblood filly was born with very thin, friable skin, skin lesions on the legs and the head, and an open abdomen. These abnormalities required euthanasia just after delivery. (Monthoux et al., 2015) [53]

Pathology: Histologic examination revealed abnormally thin dermis, markedly reduced amounts of dermal collagen bundles, with loosely orientation and abnormally large spaces between deep dermal fibers. (Monthoux et al., 2015) [53]

Prevalence: Dias et al. (2019) reported an 11% carrier frequency of the likely causal variant c.2032G>A in a sample of 374 Brazilian Warmblood horses, and hence an estimated allele frequency of 5.5%. Bellone et al. (2020) demonstrated that the PLOD1 c.2032G>A associated with WFFS is present at very low frequency [1.2%] in Thoroughbreds and is not a genetic risk factor for catastrophic breakdown. Martin et al. (2020): Among the sampled population of 7343 horses of various breeds, the overall FSS frequency was 0.56%. The FFS frequency in Warmblood type breeds was 5.32 and 0.45% in other breeds. Their Tables 1 and S1 provide estimates for individual breeds. Reiter et al. (2020): To investigate the breed distribution of the WFFS allele, 4081 horses belonging to 38 different breeds were screened. In total, 4.9% of the horses representing 21 breeds carried the WFFS allele. The affected breeds were mainly warmbloods, with carrier frequency as high as 17% in the Hanoverian and Danish Warmblood. The WFFS allele was not detected in most non-warmblood breeds. Exceptions include WFFS carriers in the Thoroughbred (17/716), Haflinger (2/48), American Sport Pony (1/12), and Knabstrupper (3/46). The origin of the WFFS allele remains unknown. Rowe et al. (2021): Warmblood Fragile Foal Syndrome genotyping was performed on hair samples from 469 horses representing 6 different breeds. Six of 303 (1.98%) sport horses tested and three of 109 (2.75%) Thoroughbreds tested were heterozygous for the WFFS polymorphism (N/WFFS). The WFFS polymorphism was not identified in the Standardbred, Cob, Connemara, or other pony breeds. Following on from the previous reports (above) of the c.2032G>A variant being detected in heterozygous (healthy) Thoroughbreds, Grillos et al. (2022) described the first reported case of a homozygous (affected) Thoroughbred foal. As a consequence, they recommended a change in the name of this disorder to fragile foal syndrome type 1 (FFS) and utilisation of genetic testing in Thoroughbreds to avoid producing affected foals. Ablondi et al. (2022): The frequency of WFFS carriers [of OMIA variant 165] calculated from a pool of 511 randomly selected SWB [Swedish Warmblood] horses born in 2017 was equal to 7.4% and ranged from 0.0 to 12.0% among the whole set of tested SWB horses, starting from 1971 till 2020. Elcombe et al. (2023) reported the c.2032G>A variant (OMIA variant 165) at a frequency of less than 1% in the US Thoroughbred population (1988-2019). [53]

Gen test: A DNA test based on the Winand (2011) patent became available commercially through Laboklin GmbHamp;Co.KG, Bad Kissingen, Germany in 2013 (Monthoux et al., 2015). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388942212 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: In a patent application, Winand (2011) documented a likely causal mutation as c.2032G>A, p.Gly678Arg in the PLOD1 gene encoding procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1. Evidence (references) - 2011. Identification of the causative mutation for inherited connective tissue disorders in equines. “United States Department Of Commerce Application Number: 61/486,464; (Filing Date: May 16th, 2011).”. http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2012158711&recNum=1&maxRec=1&office=&prevFilter=&sortOption=Pub+Date+Desc&queryString=FP%3A%28WO2012158711%29&tab=PCT+Biblio — OMIA Phene_Article / Article - 2015. Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome. BMC Vet Res — PubMed:PMID25637337 | DOI:10.1186/s12917-015-0318-8 — OMIA Phene_Article / Article - 2019. Warmblood Fragile Foal Syndrome causative single nucleotide polymorphism frequency in Warmblood horses in Brazil. Vet J — PubMed:PMID31113555 | DOI:10.1016/j.tvjl.2019.05.002 — OMIA Phene_Article / Article - 2020. Skin exhibits of Dark Ronald XX are homozygous wild type at the Warmblood fragile foal syndrome causative missense variant position in lysyl hydroxylase gene PLOD1. Anim Genet — PubMed:PMID32557718 | DOI:10.1111/age.12972 — OMIA Phene_Article / Article - 2020. Fragile Foal Syndrome (PLOD1 c.2032G>A) occurs across diverse horse populations. Anim Genet — PubMed:PMID33165934 | DOI:10.1111/age.13020 — OMIA Phene_Article / Article - 2020. Warmblood fragile foal syndrome type 1 mutation (PLOD1 c.2032G>A) is not associated with catastrophic breakdown and has a low allele frequency in the Thoroughbred breed. Equine Vet J — PubMed:PMID31502696 | DOI:10.1111/evj.13182 — OMIA Phene_Article / Article - 2020. Hanoverian F/W-line contributes to segregation of Warmblood fragile foal syndrome type 1 variant PLOD1:c.2032G>A in Warmblood horses. Equine Vet J — PubMed:PMID32323341 | DOI:10.1111/evj.13271 — OMIA Phene_Article / Article - 2020. Distribution of the Warmblood Fragile Foal Syndrome Type 1 mutation (PLOD1 c.2032G>A) in different horse breeds from Europe and the United States. Genes (Basel) — PubMed:PMID33353040 | DOI:10.3390/genes11121518 — OMIA Phene_Article / Article - 2021. Genomics in the horse industry: Discovering new questions at every turn. J Equine Vet Sci — PubMed:PMID34030792 | DOI:10.1016/j.jevs.2021.103456 — OMIA Phene_Article / Article - 2021. Warmblood fragile foal syndrome causative single nucleotide polymorphism frequency in horses in Ireland. Ir Vet J — PubMed:PMID34663462 | DOI:10.1186/s13620-021-00206-1 — OMIA Phene_Article / Article - 2021. Animal models of Ehlers-Danlos syndromes: Phenotype, pathogenesis, and translational potential. Front Genet — PubMed:PMID34712265 | DOI:10.3389/fgene.2021.726474 — OMIA Phene_Article / Article - 2021. Development of a real-time PCR assay to detect the single nucleotide polymorphism causing Warmblood Fragile Foal Syndrome. PLoS One — PubMed:PMID34748589 | DOI:10.1371/journal.pone.0259316 — OMIA Phene_Article / Article - (15 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:225400 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:153454 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [53]

Tori hobune, Estonia (Horse) — Splashed white, macchiato (hereditary; OMIA-verified breed predisposition)

Breed: Tori hobune, Estonia (Horse) [6]

Traditional Gypsy Cob, United Kingdom of Great Britain and Northern Ireland (Horse) — Neuroaxonal dystrophy, generic (hereditary; OMIA-verified breed predisposition)

Breed: Traditional Gypsy Cob, United Kingdom of Great Britain and Northern Ireland (Horse) [10]

Trakehner (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Trakehner (Horse) [22]

Trottatore Italiano, Italy (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Trottatore Italiano, Italy (Horse) [13]

Vyatka (Horse) — Coat colour, dun (hereditary; OMIA-verified breed predisposition)

Breed: Vyatka (Horse) [18]

Warmblood (Horse) — Chestnut (hereditary; OMIA-verified breed predisposition)

Breed: Warmblood (Horse) [17]

Welsh Pony (Horse) — Cerebellar abiotrophy (hereditary; OMIA-verified breed predisposition)

Breed: Welsh Pony (Horse) [22]

Zangersheide, Belgium (Horse) — Tobiano, Sabino (hereditary; OMIA-verified breed predisposition)

Breed: Zangersheide, Belgium (Horse) [13]

Zaniskari Pony (Horse) — Gaitedness, DMRT3-related (hereditary; OMIA-verified breed predisposition)

Breed: Zaniskari Pony (Horse) [19]

Species-Specific Health

Horse (Equus caballus) — Atypical myopathy (hereditary; OMIA-verified species predisposition)

Species: Horse (Equus caballus) [54]

Disorder: Atypical myopathy [54]

Summary: Sander et al. (2021): "Several thousands of severe, often letal cases of atypical myopathy (AM) caused by the ingestion of seeds and seedlings of some Acer species have been observed in horses and other equids, occurring in all age groups from the very young to the very old animals [for review see Votion et al. (2020)]. Hypoglycin A (HGA) and methylenecyclopropylglycine (MCPG) are the constituents responsible for this. Newborn foals, however, that do not yet consume green forage themselves and therefore can receive Acer toxins prenatally only via the placenta or postnatally with the milk are apparently very rarely affected by AM.. we hypothesize that the low concentrations of active maple toxins to be expected in a foal fed with collostrum or milk will only lead to acute disease if there is a special, possibly genetically determined sensitivity." Sander et al. (2021) investigated a single foal with severe atypical myopathy and identified an "extensive loss of function of the enzyme. long-chain enoyl-CoA hydratase (OMIM 609015, EC 4.2.1.74). The enzyme is, at least in humans, integrated into the mitochondrial trifunctional protein which also harbors the ß-hydroxy-acyl-CoA dehydrogenase and long-chain thiolase.. Whether a genetic defect could underlie the present case would have had to be proven by appropriate genetic studies. Unfortunately, no suitable tissue was available." Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2021. Severe inhibition of long-chain acyl-CoA enoylhydratase (EC 4.2.1.74) in a newborn foal suffering from atypical myopathy. Front Vet Sci — PubMed:PMID34765670 | DOI:10.3389/fvets.2021.765623 — OMIA Phene_Article / Article - 2020. Answers to the frequently asked questions regarding horse feeding and management practices to reduce the risk of atypical myopathy. Animals (Basel) — PubMed:PMID32102384 | DOI:10.3390/ani10020365 — OMIA Phene_Article / Article - 2024. Large-scale study of blood markers in equine atypical myopathy reveals subclinical poisoning and advances in diagnostic and prognostic criteria. Environ Toxicol Pharmacol — PubMed:PMID39032580 | DOI:10.1016/j.etap.2024.104515 — OMIA Phene_Article / Article - 2021. Severe inhibition of long-chain acyl-CoA enoylhydratase (EC 4.2.1.74) in a newborn foal suffering from atypical myopathy. Front Vet Sci — PubMed:PMID34765670 | DOI:10.3389/fvets.2021.765623 — OMIA Phene_Article / Article - 2020. Answers to the frequently asked questions regarding horse feeding and management practices to reduce the risk of atypical myopathy. Animals (Basel) — PubMed:PMID32102384 | DOI:10.3390/ani10020365 — OMIA Phene_Article / Article - 2024. Large-scale study of blood markers in equine atypical myopathy reveals subclinical poisoning and advances in diagnostic and prognostic criteria. Environ Toxicol Pharmacol — PubMed:PMID39032580 | DOI:10.1016/j.etap.2024.104515 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:609015 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600890 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:143450 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:609015 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600890 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:143450 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [54]

Horse (Equus caballus) — Cerebellar abiotrophy (hereditary; OMIA-verified species predisposition)

Disorder: Cerebellar abiotrophy [22]

Mode of inheritance: “Results of the complex segregation analysis were consistent with a single Mendelian autosomal recessive mode of inheritance” (Brault et al., AJVR, 2011). {text provided by Meredith O’Connell, working under the supervision of Professor E. Bailey} [22]

Clin feat: Brault et al. 2011 (Genomics): "Cerebellar abiotrophy (CA) is a neurological condition, characterized by post-natal degeneration of Purkinje cells of the cerebellum... Symptoms of CA in horses generally appear between six weeks and four months of age and include intention head tremors, ataxia, exaggerated or paddling action of the forelegs, a wide-based stance and a lack of menace response.... Affected horses may startle easily and fall, and are often unable to rise from a reclining position”. {slightly modified from text provided by Meredith O’Connell, working under the supervision of Professor E. Bailey} [22]

Horse (Equus caballus) — Dwarfism, ACAN-related (hereditary; OMIA-verified species predisposition)

Disorder: Dwarfism, ACAN-related [38]

Horse (Equus caballus) — Equine rhabdomyolysis syndrome; Polysaccharide storage myopathy; Tying-up (hereditary; OMIA-verified species predisposition)

Mode of inheritance: The disorder is definitely familial, and there are suggestions of autosomal recessive inheritance. However, the published data are inconclusive on this point (Valberg et al., 1996). Dranchak et al. (2005) performed a segregation analysis that excluded all forms of single-locus inheritance other than autosomal dominant. [8]

Clin feat: As summarised by McCue et al. (2008): "The phenotypic expression of PSSM ranges from muscle atrophy and progressive weakness in Draft horse breeds to muscle soreness and gait abnormalities in Warmblood breeds, and acute exertional rhabdomyolysis in Quarter Horses. The severity of clinical signs in PSSM ranges from muscle cramping and stretching out... to severe muscle pain and myoglobinuria and occasionally the complete inability to rise". [8]

Prevalence: As reported by McCue et al. (2008), "The His309 allele was found in either heterozygous or homozygous form in 356 horses from 15 different breeds including Quarter Horses, Paint horses, Appaloosa horses, 5 Draft horse breeds, 3 Warmblood breeds, the Morgan, Mustang, Rocky Mountain Horse breeds, as well as mixed breed horses and Warmblood horses of unspecified breed." Its frequency ranged "from 0.035 to 0.350 in different breeds". The presence of this allele in so many breeds suggests ancient origins. McCue et al. (2008) estimated its mean age at 159 generations, which means that "this mutation likely originated between 1200 to 1500 years ago..., prior to the separation of the modern breeds known today". McCoy et al. (2013) reported evidence that the 309His "mutation underwent historical selection in the Belgian [because "Under historical conditions of daily work and limited feed, excess muscle glycogen may have been advantageous"], but not in the Quarter Horse". Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: GSY1 (Entrez Gene ID 4157416) — OMIA Phene_Gene / GeneSynonym - OMIA molecular-genetics note: Noting that the only functional comparative gene in the candidate region of HSA19 was GYS1, McCue et al. (2008) sequenced this gene in a likely homozygous affected horse and a control horse, discovering a missense mutation (c.?G>A; p.Arg309His) whose segregation in other affected and normal horses was consistent with causality. Interestingly, McCue et al. (2008) presented evidence that this is … Evidence (references) - 1993. Muscle Histopathology and Plasma Aspartate Aminotrausferase, Creatine Kinase and Myoglobin Changes with Exercise in Horses with Recurrent Exertional Rhabdomyolysis (Erratum for Vol 25, Pg 11, 1993). Equine Veterinary Journal — OMIA Phene_Article / Article - 1993. Caffeine Contractures, Twitch Characteristics and the Threshold for Ca-2+-Induced Ca-2+ Release in Skeletal Muscle from Horses with Chronic Intermittent Rhabdomyolysis. Research in Veterinary Science — PubMed:PMID8434138 — OMIA Phene_Article / Article - 1996. Familial basis of exertional rhabdomyolysis in quarter horse-related breeds. American Journal of Veterinary Research — PubMed:PMID8669756 — OMIA Phene_Article / Article - 1997. Chronic exertional rhabdomyolysis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1997. Genetic markers in standardbred trotters susceptible to the rhabdomyolysis syndrome. Equine Veterinary Journal — PubMed:PMID9104560 — OMIA Phene_Article / Article - 1997. Exertional rhabdomyolysis and polysaccharide storage myopathy in horses. Compendium on Continuing Education for the Practicing Veterinarian — OMIA Phene_Article / Article - 1998. Exertional rhabdomyolysis. Equine Practice — OMIA Phene_Article / Article - 1998. Dietary control of exertional rhabdomyolysis in horses. Journal of the American Veterinary Medical Association — OMIA Phene_Article / Article - 1998. Renal failure, laminitis, and colitis following severe rhabdomyolysis in a draft horse-cross with polysaccharide storage myopathy. Canadian Veterinary Journal - Revue Veterinaire Canadienne — OMIA Phene_Article / Article - 1998. Skeletal muscle glycolytic capacity and phosphofructokinase regulation in horses with polysaccharide storage myopathy. American Journal of Veterinary Research — PubMed:PMID9622752 — OMIA Phene_Article / Article - 1999. Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy. Equine Veterinary Journal — PubMed:PMID9952328 — OMIA Phene_Article / Article - 1999. Postanaesthetic recumbency in a Belgian filly with polysaccharide storage myopathy. Veterinary Record — PubMed:PMID10070692 — OMIA Phene_Article / Article - (92 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:611556 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [8]

Horse (Equus caballus) — Gray; Grey; Greying with age (hereditary; OMIA-verified species predisposition)

Disorder: Gray; Grey; Greying with age [55]

Summary: Grey horses are born with normal pigmentation, but gradually lose their pigmentation as they age, until, typically at around 6-12 years old, they become white, while retaining dark skin pigmentation. Included with this phenotype is a relatively high incidence of dermal melanomas, and an associated decrease in life expectancy (see OMIA:002231-9796: Melanoma, generic in Equus caballus) [55]

Gen test: Since exactly the same mutation is completely associated with the grey phenotype in more than 850 horses from numerous breeds (Rosengren Pielberg et al., 2008), it is very likely that a single DNA test will suffice to detect virtually all occurrences of the grey alleles. Kavar et al. (2012) provide details of a robust DNA test. Nowacka-Woszuk et al. (2021) provide methods for using ddPCR to detect copy number which can help in distinguishing between the G1, G2, and G3 alleles. Horses with only a G1 allele will not be grey, and therefore some testing laboratories report this allele as N (for normal). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4157477 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Rosengren Pielberg et al. (2008) presented convincing evidence that this classic phenotype is due to a 4.6kb intronic duplication in the gene for syntaxin-17 (STX17). This duplication appears to increase the expression of both syntaxin-17 and a neighbouring gene NR4A3, which encodes nuclear receptor subfamily 4, group A, member 3. Whilst the details are still to be elucidated, Pielberg et al. (200… Evidence (references) - 2002. Genetic mapping of the (G)-locus, responsible for the coat color phenotype "progressive greying with age" in horses (Equus caballus). Mammalian Genome — PubMed:PMID12370784 | DOI:10.1007/s00335-002-2174-7 — OMIA Phene_Article / Article - 2002. Linkage of the grey coat colour locus to microsatellites on horse chromosome 25. Animal Genetics — PubMed:PMID12354140 — OMIA Phene_Article / Article - 2002. Assignment of the horse grey coat colour gene to ECA25 using whole genome scanning. Animal Genetics — PubMed:PMID12354141 — OMIA Phene_Article / Article - 2005. Comparative linkage mapping of the Grey coat colour gene in horses. Anim Genet — PubMed:PMID16167981 | DOI:10.1111/j.1365-2052.2005.01334.x — OMIA Phene_Article / Article - 2008. A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse. Nature Genetics — PubMed:PMID18641652 | DOI:10.1038/ng.185 — OMIA Phene_Article / Article - 1977. [Comparative investigations of depigmented and melanomatous lesions in gray horses of the lipizzaner breed (author's transl)]. Arch Dermatol Res — PubMed:PMID900991 — OMIA Phene_Article / Article - 2004. Comparative histopathology of grey-horse-melanoma and human malignant melanoma. Pigment Cell Res — PubMed:PMID15541026 | DOI:10.1111/j.1600-0749.2004.00192.x — OMIA Phene_Article / Article - 2003. Equine melanoma in a population of 296 grey Lipizzaner horses. Equine Vet J — PubMed:PMID12638791 — OMIA Phene_Article / Article - 2001. Disseminated metastatic intramedullary melanoma in an aged grey horse. J Comp Pathol — PubMed:PMID11578137 | DOI:10.1053/jcpa.2001.0481 — OMIA Phene_Article / Article - 2001. Tumor regression induced by intratumoral injection of DNA coding for human interleukin 12 into melanoma metastases in gray horses. J Mol Med — PubMed:PMID11434722 — OMIA Phene_Article / Article - 2000. The study of cutaneous melanomas in Camargue-type gray-skinned horses (2): epidemiological survey. Pigment Cell Res — PubMed:PMID10761996 — OMIA Phene_Article / Article - 2000. The study of cutaneous melanomas in Camargue-type gray-skinned horses (1): clinical-pathological characterization. Pigment Cell Res — PubMed:PMID10761995 — OMIA Phene_Article / Article - (31 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:604204 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [55]

Horse (Equus caballus) — Hyperkalemic Periodic Paralysis (HYPP) (hereditary; OMIA-verified species predisposition)

Mode of inheritance: Naylor et al. (1999) compared the clinical responses of heterozygotes to homozygotes for the variant causing HYPP and determined that homozygotes are more severely affected, demonstrating the partial dominant mode of inheritance. {text supplied by Professor E. Bailey and students; 20 March 2019} [48]

Horse (Equus caballus) — Junctional epidermolysis bullosa (hereditary; OMIA-verified species predisposition)

Mode of inheritance: A mare produced two affected foals when bred to two different stallions (Kohn et al., 1989). Similarity to a hereditary condition in people suggested a recessive, autosomal mode of inheritance. Histological studies suggested an absence of the LAMC2 gene product, making this a primary candidate gene for sequencing. After the variant in LAMC2 was identified a pedigree study involving 148 Belgian horses from the United States confirmed the autosomal recessive mode of inheritance (Spirito et al., 2002). [27]

Clin feat: "Lesions can be present at birth or develop over a short period of time and are characterized by the development of vesicles and bullae that rapidly progress to erosions and ulcerations at sites of minor trauma such as the lips, the oral mucosa, and distal extremities and the coronary band, with resulting sloughing of the hoofs.. Lesions can be secondarily affected or become pustules. Affected animals may die soon after birth due to inability to suckle.“ (Capelli et al. 2015) [27]

Pathology: Spirito et al. (2002): "Electron microscopy examination revealed junctional blistering and abnormal hemidesmosomes (Johnson et al., 1988)" Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 3645968 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene Evidence (references) - 1988. Hereditary junctional mechanobullous disease in a foal. Journal of the American Veterinary Medical Association — PubMed:PMID3209456 — OMIA Phene_Article / Article - 1995. Mechanobullous disease in a Belgian foal in eastern Ontario. Canadian Veterinary Journal — OMIA Phene_Article / Article - 1989. Mechanobullous disease in two Belgian foals. Equine Veterinary Journal — PubMed:PMID2767032 — OMIA Phene_Article / Article - 1988. Ultrastructure of junctional epidermolysis bullosa in Belgian foals. J Comp Pathol — PubMed:PMID3204167 | DOI:10.1016/0021-9975(88)90053-9 — OMIA Phene_Article / Article - 2003. A mutation in the LAMC2 gene causes the Herlitz junctional epidermolysis bullosa (H-JEB) in two French draft horse breeds. Genetics Selection Evolution — PubMed:PMID12633536 | DOI:10.1051/gse:2003007 — OMIA Phene_Article / Article - 2002. Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse. J Invest Dermatol — PubMed:PMID12230513 | DOI:10.1046/j.1523-1747.2002.01852.x — OMIA Phene_Article / Article - 2003. Junctional epidermolysis bullosa in Belgian draft horses. Proc Am Assoc Equine Practnr — OMIA Phene_Article / Article - 2015. First report of junctional epidermolysis bullosa (JEB) in the Italian draft horse. BMC Vet Res — PubMed:PMID25889423 | DOI:10.1186/s12917-015-0374-0 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:226700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:226650 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:150292 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [27]

Horse (Equus caballus) — Laminitis (hereditary; OMIA-verified species predisposition)

Disorder: Laminitis [56]

Summary: See also 'OMIA:001898-9796: Metabolic syndrome in Equus caballus' Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1995. Descriptive epidemiological study of equine laminitis. Equine Veterinary Journal — PubMed:PMID8654351 — OMIA Phene_Article / Article - 1995. Haematological changes observed in andalusian horses with laminitis. Journal of Veterinary Medical Science — PubMed:PMID8593320 — OMIA Phene_Article / Article - 1996. Client information series - laminitis. Equine Practice — OMIA Phene_Article / Article - 1997. Equine laminitis - a review of recent research. Equine Practice — OMIA Phene_Article / Article - 1997. Age, breed, sex and seasonality as risk factors for equine laminitis. Preventive Veterinary Medicine — PubMed:PMID9234403 — OMIA Phene_Article / Article - 1997. New aspects of laminitis in horses [German]. Tierarztliche Umschau — OMIA Phene_Article / Article - 1997. Laminitis. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 1995. Control of genetically determined diseases and defects in Swedish horse breeding. Equine Veterinary Journal — OMIA Phene_Article / Article - 1998. Step by painful step - increasing knowledge about laminitis. Equine Veterinary Journal — PubMed:PMID9535061 — OMIA Phene_Article / Article - 1999. Historical perspectives on laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1999. Pharmacologic and alternative therapies for the horse with chronic laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1999. The pathophysiology of developmental and acute laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - (65 additional references in OMIA) - 1995. Descriptive epidemiological study of equine laminitis. Equine Veterinary Journal — PubMed:PMID8654351 — OMIA Phene_Article / Article - 1995. Haematological changes observed in andalusian horses with laminitis. Journal of Veterinary Medical Science — PubMed:PMID8593320 — OMIA Phene_Article / Article - 1996. Client information series - laminitis. Equine Practice — OMIA Phene_Article / Article - 1997. Equine laminitis - a review of recent research. Equine Practice — OMIA Phene_Article / Article - 1997. Age, breed, sex and seasonality as risk factors for equine laminitis. Preventive Veterinary Medicine — PubMed:PMID9234403 — OMIA Phene_Article / Article - 1997. New aspects of laminitis in horses [German]. Tierarztliche Umschau — OMIA Phene_Article / Article - 1997. Laminitis. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 1995. Control of genetically determined diseases and defects in Swedish horse breeding. Equine Veterinary Journal — OMIA Phene_Article / Article - 1998. Step by painful step - increasing knowledge about laminitis. Equine Veterinary Journal — PubMed:PMID9535061 — OMIA Phene_Article / Article - 1999. Historical perspectives on laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1999. Pharmacologic and alternative therapies for the horse with chronic laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - 1999. The pathophysiology of developmental and acute laminitis. Veterinary Clinics of North America - Equine Practice — OMIA Phene_Article / Article - (65 additional references in OMIA) [56]

Horse (Equus caballus) — Lavender Foal Syndrome, Coat Color Dilution Lethal (hereditary; OMIA-verified species predisposition)

Disorder: Lavender Foal Syndrome, Coat Color Dilution Lethal [57]

Clin feat: Brooks et al. (2010): "Affected foals can display an array of neurological signs including tetanic-like seizures, opisthotonus, stiff or paddling leg movements and nystagmus. [Fanelli, 2005]. Mild leucopenia is sometimes observed [Fanelli, 2005; Page et al., 2006]. These neurologic impairments prevent the foal from standing and nursing normally and, if not lethal on their own, are often cause for euthanasia. In addition to these abnormalities, affected foals possess a characteristic diluted “lavender” coat color. This resulting coat color, variously described as pale gray, pewter, and light chestnut, as well as lavender, has coined the name “Lavender Foal Syndrome” (LFS) [Fanelli, 2005]." Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 40954081 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Brooks et al. (2010) identified a deletion in the MYO5A gene as being responsible for this disorder in Arabian horses. This gene has the interim symbol of LOC100069548. Evidence (references) - 2010. Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for Lavender Foal Syndrome. PLoS Genet — PubMed:PMID20419149 | DOI:10.1371/journal.pgen.1000909 — OMIA Phene_Article / Article - 2005. Coat colour dilution lethal ("lavender foal syndrome"): a tetany syndrome of Arabian foals. Equine Veterinary Education — OMIA Phene_Article / Article - 2006. Clinical, clinicopathologic, postmortem examination findings and familial history of 3 Arabians with lavender foal syndrome. J Vet Intern Med — PubMed:PMID17186871 — OMIA Phene_Article / Article - 2010. Pleiotropic effects of pigmentation genes in horses. Anim Genet — PubMed:PMID21070283 | DOI:10.1111/j.1365-2052.2010.02116.x — OMIA Phene_Article / Article - 2012. Investigation of allele frequencies for Lavender foal syndrome in the horse. Anim Genet — PubMed:PMID22497275 | DOI:10.1111/j.1365-2052.2011.02305.x — OMIA Phene_Article / Article - 2014. The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Vet J — PubMed:PMID24033554 | DOI:10.1111/evj.12177 — OMIA Phene_Article / Article - 2019. Genetic screening for cerebellar abiotrophy, severe combined immunodeficiency and lavender foal syndrome in Arabian horses in Poland. Vet J — PubMed:PMID31113566 | DOI:10.1016/j.tvjl.2019.04.012 — OMIA Phene_Article / Article - 2021. Investigation of cerebellar abiotrophy (CA), Lavender Foal Syndrome (LFS), and severe combined immunodeficiency (SCID) variants in a cohort of three MENA region horse breeds. Genes (Basel) — PubMed:PMID34946842 | DOI:10.3390/genes12121893 — OMIA Phene_Article / Article - 2023. Evidence for origin of lavender foal syndrome among Egyptian Arabian horses in Egypt. Equine Vet J — PubMed:PMID35665534 | DOI:10.1111/evj.13604 — OMIA Phene_Article / Article - 2026. Genomic diversity and structure in arabian horses revealed by whole-genome sequencing: establishment of an allele frequency database of common genetic variation. BMC Genomics — PubMed:PMID42010471 | DOI:10.1186/s12864-026-12862-0 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:214450 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:160777 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [57]

Horse (Equus caballus) — Male subfertility (hereditary; OMIA-verified species predisposition)

Disorder: Male subfertility [58]

Summary: See also OMIA:001762-9796: Impaired acrosomal reaction in Equus caballus (horse) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2012. Genome-wide association study implicates testis-sperm specific FKBP6 as a susceptibility locus for impaired acrosome reaction in stallions. PLoS Genet — PubMed:PMID23284302 | DOI:10.1371/journal.pgen.1003139 — OMIA Phene_Article / Article - 2022. Copy number variation of horse Y chromosome genes in normal equine populations and in horses with abnormal sex development and subfertility: relationship of copy number variations with Y haplogroups. G3 (Bethesda) — PubMed:PMID36227030 | DOI:10.1093/g3journal/jkac278 — OMIA Phene_Article / Article - 2024. Proteomic analysis of sperm from fertile stallions and subfertile stallions due to impaired acrosomal exocytosis. Sci Rep — PubMed:PMID38816557 | DOI:10.1038/s41598-024-63410-3 — OMIA Phene_Article / Article - 2024. Spermatozoal acrosome dysfunction and its role in stallion subfertility. J Equine Vet Sci — PubMed:PMID39490453 | DOI:10.1016/j.jevs.2024.105213 — OMIA Phene_Article / Article - 2012. Genome-wide association study implicates testis-sperm specific FKBP6 as a susceptibility locus for impaired acrosome reaction in stallions. PLoS Genet — PubMed:PMID23284302 | DOI:10.1371/journal.pgen.1003139 — OMIA Phene_Article / Article - 2022. Copy number variation of horse Y chromosome genes in normal equine populations and in horses with abnormal sex development and subfertility: relationship of copy number variations with Y haplogroups. G3 (Bethesda) — PubMed:PMID36227030 | DOI:10.1093/g3journal/jkac278 — OMIA Phene_Article / Article - 2024. Proteomic analysis of sperm from fertile stallions and subfertile stallions due to impaired acrosomal exocytosis. Sci Rep — PubMed:PMID38816557 | DOI:10.1038/s41598-024-63410-3 — OMIA Phene_Article / Article - 2024. Spermatozoal acrosome dysfunction and its role in stallion subfertility. J Equine Vet Sci — PubMed:PMID39490453 | DOI:10.1016/j.jevs.2024.105213 — OMIA Phene_Article / Article [58]

Horse (Equus caballus) — Melanoma, generic (hereditary; OMIA-verified species predisposition)

Disorder: Melanoma, generic [59]

Summary: see also OMIA:001356-9796: Coat colour, grey/gray in Equus caballus as gray horses have an increased risk of developing melanomas Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - OMIA molecular-genetics note: Wong et al. (2019) performed "a cross-species analysis by sequencing tumor-germline pairs from 46 primary human muscosal, 65 primary canine oral and 28 primary equine melanoma cases from mucosal sites. ... As the gray phenotype, associated with progressive silvering of colored hair, has been linked to melanoma development in horses, we obtained a coat color phenotype for each case from clinical re… Evidence (references) - 2019. Genetic and environmental risk factors for vitiligo and melanoma in Pura Raza Español horses. Equine Vet J — PubMed:PMID30624804 | DOI:10.1111/evj.13067 — OMIA Phene_Article / Article - 2022. DPF3, a putative candidate gene for melanoma etiopathogenesis in gray horses. J Equine Vet Sci — PubMed:PMID34801788 | DOI:10.1016/j.jevs.2021.103797 — OMIA Phene_Article / Article - 2023. Administration and detection of gene therapy in horses: A systematic review. Drug Test Anal — PubMed:PMID36269665 | DOI:10.1002/dta.3394 — OMIA Phene_Article / Article - 2013. Malignant melanoma in a grey horse: case presentation and review of equine melanoma treatment options. Ir Vet J — PubMed:PMID24196087 | DOI:10.1186/2046-0481-66-22 — OMIA Phene_Article / Article - 2023. Interventions for treatment of cutaneous melanoma in horses: a structured literature review. Vet Res Commun — PubMed:PMID36329228 | DOI:10.1007/s11259-022-10023-8 — OMIA Phene_Article / Article - 2013. Melanoma in horses: Current perspectives. Equine Veterinary Education — DOI:doi.org/10.1111/j.2042-3292.2011.00368.x — OMIA Phene_Article / Article - 2019. Cross-species genomic landscape comparison of human mucosal melanoma with canine oral and equine melanoma. Nat Commun — PubMed:PMID30664638 | DOI:10.1038/s41467-018-08081-1 — OMIA Phene_Article / Article - 2024. White horses - non-coding sequences drive premature hair greying and predisposition to melanoma. Ups J Med Sci — PubMed:PMID38571883 | DOI:10.48101/ujms.v129.10626 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Deregulation of metalloproteinase expression in gray horse melanoma ex vivo and in vitro. Cells — PubMed:PMID38891088 | DOI:10.3390/cells13110956 — OMIA Phene_Article / Article - 2024. An intronic copy number variation in Syntaxin 17 determines speed of greying and melanoma incidence in Grey horses. Nat Commun — PubMed:PMID39209879 | DOI:10.1038/s41467-024-51898-2 — OMIA Phene_Article / Article - 2024. Equine Melanoma Updates. Vet Clin North Am Equine Pract — PubMed:PMID39266414 | DOI:10.1016/j.cveq.2024.07.008 — OMIA Phene_Article / Article - (11 additional references in OMIA) [59]

Horse (Equus caballus) — Metabolic syndrome (hereditary; OMIA-verified species predisposition)

Disorder: Metabolic syndrome [60]

Summary: McGowan and Irland (2023): "Equine metabolic syndrome is not a disease, but a collection of risk factors for endocrinopathic laminitis with the defining feature of the syndrome being insulin dysregulation (ID) [Durham et al., 2018]. Risk factors for EMS include age, female sex, breed, being more sedentary and obesity [Durham et al., 2018; Carslake et al., 2021]." Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2012. Diabetes, insulin resistance, and metabolic syndrome in horses. J Diabetes Sci Technol — PubMed:PMID22768883 | DOI:10.1177/193229681200600307 — OMIA Phene_Article / Article - 2019. Heritability of metabolic traits associated with equine metabolic syndrome in Welsh ponies and Morgan horses. Equine Vet J — PubMed:PMID30472742 | DOI:10.1111/evj.13053 — OMIA Phene_Article / Article - 2019. A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome. Vet J — PubMed:PMID31492392 | DOI:10.1016/j.tvjl.2019.105341 — OMIA Phene_Article / Article - 2020. Preliminary analysis of the FAM174A gene suggests it lacks a strong association with equine metabolic syndrome in ponies. Domest Anim Endocrinol — PubMed:PMID32169753 | DOI:10.1016/j.domaniend.2020.106439 — OMIA Phene_Article / Article - 2017. Genomewide association study reveals a risk locus for equine metabolic syndrome in the Arabian horse. J Anim Sci — PubMed:PMID28380523 | DOI:10.2527/jas.2016.1221 — OMIA Phene_Article / Article - 2019. Genome-Wide Association Analyses of Equine Metabolic Syndrome Phenotypes in Welsh Ponies and Morgan Horses. Genes (Basel) — PubMed:PMID31698676 | DOI:10.3390/genes10110893 — OMIA Phene_Article / Article - 2019. Genetics of equine metabolic syndrome. Vet Rec — PubMed:PMID31371685 | DOI:10.1136/vr.l4725 — OMIA Phene_Article / Article - 2015. Equine metabolic syndrome. Vet Rec — PubMed:PMID26273009 | DOI:10.1136/vr.103226 — OMIA Phene_Article / Article - 2011. Equine metabolic syndrome. Vet Clin North Am Equine Pract — PubMed:PMID21392655 | DOI:10.1016/j.cveq.2010.12.004 — OMIA Phene_Article / Article - 2010. Equine metabolic syndrome. J Vet Intern Med — PubMed:PMID20384947 | DOI:10.1111/j.1939-1676.2010.0503.x — OMIA Phene_Article / Article - 2002. The equine metabolic syndrome peripheral Cushing's syndrome. Vet Clin North Am Equine Pract — PubMed:PMID15635908 | DOI:10.1016/s0749-0739(02)00006-8 — OMIA Phene_Article / Article - 2020. The genetic basis of obesity and related metabolic diseases in humans and companion animals. Genes — PubMed:PMID33233816 | DOI:10.3390/genes11111378 — OMIA Phene_Article / Article - (38 additional references in OMIA) - 2012. Diabetes, insulin resistance, and metabolic syndrome in horses. J Diabetes Sci Technol — PubMed:PMID22768883 | DOI:10.1177/193229681200600307 — OMIA Phene_Article / Article - 2019. Heritability of metabolic traits associated with equine metabolic syndrome in Welsh ponies and Morgan horses. Equine Vet J — PubMed:PMID30472742 | DOI:10.1111/evj.13053 — OMIA Phene_Article / Article - 2019. A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome. Vet J — PubMed:PMID31492392 | DOI:10.1016/j.tvjl.2019.105341 — OMIA Phene_Article / Article - 2020. Preliminary analysis of the FAM174A gene suggests it lacks a strong association with equine metabolic syndrome in ponies. Domest Anim Endocrinol — PubMed:PMID32169753 | DOI:10.1016/j.domaniend.2020.106439 — OMIA Phene_Article / Article - 2017. Genomewide association study reveals a risk locus for equine metabolic syndrome in the Arabian horse. J Anim Sci — PubMed:PMID28380523 | DOI:10.2527/jas.2016.1221 — OMIA Phene_Article / Article - 2019. Genome-Wide Association Analyses of Equine Metabolic Syndrome Phenotypes in Welsh Ponies and Morgan Horses. Genes (Basel) — PubMed:PMID31698676 | DOI:10.3390/genes10110893 — OMIA Phene_Article / Article - 2019. Genetics of equine metabolic syndrome. Vet Rec — PubMed:PMID31371685 | DOI:10.1136/vr.l4725 — OMIA Phene_Article / Article - 2015. Equine metabolic syndrome. Vet Rec — PubMed:PMID26273009 | DOI:10.1136/vr.103226 — OMIA Phene_Article / Article - 2011. Equine metabolic syndrome. Vet Clin North Am Equine Pract — PubMed:PMID21392655 | DOI:10.1016/j.cveq.2010.12.004 — OMIA Phene_Article / Article - 2010. Equine metabolic syndrome. J Vet Intern Med — PubMed:PMID20384947 | DOI:10.1111/j.1939-1676.2010.0503.x — OMIA Phene_Article / Article - 2002. The equine metabolic syndrome peripheral Cushing's syndrome. Vet Clin North Am Equine Pract — PubMed:PMID15635908 | DOI:10.1016/s0749-0739(02)00006-8 — OMIA Phene_Article / Article - 2020. The genetic basis of obesity and related metabolic diseases in humans and companion animals. Genes — PubMed:PMID33233816 | DOI:10.3390/genes11111378 — OMIA Phene_Article / Article - (38 additional references in OMIA) [60]

Horse (Equus caballus) — Multiple acyl-CoA dehydrogenase deficiency (hereditary; OMIA-verified species predisposition)

Disorder: Multiple acyl-CoA dehydrogenase deficiency [61]

Mode of inheritance: Because this disorder is due to the ingestion of a toxin, it is not inherited. It is included in OMIA because it is a phenocopy of an inherited disorder that occurs in humans (see MIM entry above) and in cats (see OMIA 001457-9685). [61]

Summary: This equine disorder is an interesting example of a phenocopy, i.e. the phenotype of an inherited disorder that has a non-genetic cause. In this case, the non-genetic cause is ingestion of a toxin from microbes on plant leaves. In humans, there are inherited forms of this disorder due to mutations in three different genes (ETFA, ETFB, ETFDH) whose peptides are involved in electron transfer in the mitochondrial respiratory chain: see the MIM entry above. For another example of a phenocopy, see OMIA 000625-9913. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1959. Contribution a l'etude de la pathogenie et du traitement de la myoglobinurie paroxystique due cheval. Revue de Medecine Veterinaire — OMIA Phene_Article / Article - 2008. Acquired multiple Acyl-CoA dehydrogenase deficiency in 10 horses with atypical myopathy. Neuromuscular Disorders — PubMed:PMID18406615 | DOI:10.1016/j.nmd.2008.02.007 — OMIA Phene_Article / Article - 2013. [Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) in the horse]. Tijdschr Diergeneeskd — PubMed:PMID23847852 — OMIA Phene_Article / Article - 2012. Equine multiple acyl-CoA dehydrogenase deficiency (MADD) associated with seasonal pasture myopathy in the midwestern United States. J Vet Intern Med — PubMed:PMID22708588 | DOI:10.1111/j.1939-1676.2012.00957.x — OMIA Phene_Article / Article - 2007. Equine biochemical multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of rhabdomyolysis. Mol Genet Metab — PubMed:PMID17540595 | DOI:10.1016/j.ymgme.2007.04.010 — OMIA Phene_Article / Article - 2010. Equine acquired multiple acyl-CoA dehydrogenase deficiency (MADD) in 14 horses associated with ingestion of Maple leaves (Acer pseudoplatanus) covered with European tar spot (Rhytisma acerinum). Mol Genet Metab — PubMed:PMID20655779 | DOI:10.1016/j.ymgme.2010.06.019 — OMIA Phene_Article / Article - 2011. Decreased oxidative phosphorylation and PGAM deficiency in horses suffering from atypical myopathy associated with acquired MADD. Mol Genet Metab — PubMed:PMID21843962 | DOI:10.1016/j.ymgme.2011.07.022 — OMIA Phene_Article / Article - 1959. Contribution a l'etude de la pathogenie et du traitement de la myoglobinurie paroxystique due cheval. Revue de Medecine Veterinaire — OMIA Phene_Article / Article - 2008. Acquired multiple Acyl-CoA dehydrogenase deficiency in 10 horses with atypical myopathy. Neuromuscular Disorders — PubMed:PMID18406615 | DOI:10.1016/j.nmd.2008.02.007 — OMIA Phene_Article / Article - 2013. [Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) in the horse]. Tijdschr Diergeneeskd — PubMed:PMID23847852 — OMIA Phene_Article / Article - 2012. Equine multiple acyl-CoA dehydrogenase deficiency (MADD) associated with seasonal pasture myopathy in the midwestern United States. J Vet Intern Med — PubMed:PMID22708588 | DOI:10.1111/j.1939-1676.2012.00957.x — OMIA Phene_Article / Article - 2007. Equine biochemical multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of rhabdomyolysis. Mol Genet Metab — PubMed:PMID17540595 | DOI:10.1016/j.ymgme.2007.04.010 — OMIA Phene_Article / Article - 2010. Equine acquired multiple acyl-CoA dehydrogenase deficiency (MADD) in 14 horses associated with ingestion of Maple leaves (Acer pseudoplatanus) covered with European tar spot (Rhytisma acerinum). Mol Genet Metab — PubMed:PMID20655779 | DOI:10.1016/j.ymgme.2010.06.019 — OMIA Phene_Article / Article - 2011. Decreased oxidative phosphorylation and PGAM deficiency in horses suffering from atypical myopathy associated with acquired MADD. Mol Genet Metab — PubMed:PMID21843962 | DOI:10.1016/j.ymgme.2011.07.022 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:231680 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:231675 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:231680 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:231675 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [61]

Horse (Equus caballus) — Night blindness, congenital stationary, GRM6-related (hereditary; OMIA-verified species predisposition)

Disorder: Night blindness, congenital stationary, GRM6-related [16]

Prevalence: Hack et al. (2021): "This variant [GRM6 c.533C>T] was not detected in 273 horses from three additional breeds. The estimated allele frequency in Tennessee Walking Horses is 10%." Esdaile et al. (2024): "The CSNB2 allele was present in nine breeds [American Quarter Horse, Racking Horse, Rocky Mountain Horse, American Saddlebred, Spotted Saddle Horse, Standardbred (pacer), Miniature Horse, Missouri Fox Trotting Horse, Morgan], ranging in frequency from 0.0010 in American Quarter Horses (n = 486) to 0.17 in pacing Standardbreds (n = 110.). The CSNB2 allele was not detected in trotting Standardbreds (n = 70), Thoroughbreds (n = 1787), Hackney Horses (n = 47), Hackney Ponies (n = 44), and Shetland Ponies (n = 99.). Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 388955788 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Hack et al. (2021): "WGS [whole genome sequencing] analysis identified a missense mutation in metabotropic glutamate receptor 6 (GRM6) (c.533C>T p.Thr178Met)." Evidence (references) - 2021. Whole-genome sequencing identifies missense mutation in GRM6 as the likely cause of congenital stationary night blindness in a Tennessee Walking Horse. Equine Vet J — PubMed:PMID32654228 | DOI:10.1111/evj.13318 — OMIA Phene_Article / Article - 2024. Additional evidence supports GRM6 p.Thr178Met as a cause of congenital stationary night blindness in three horse breeds. Vet Ophthalmol — PubMed:PMID37815029 | DOI:10.1111/vop.13151 — OMIA Phene_Article / Article - 2024. Consensus guidelines for nomenclature of companion animal inherited retinal disorders. Vet Ophthalmol — PubMed:PMID38334230 | DOI:10.1111/vop.13185 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:604096 (type: gene) — OMIA Group_OMIM (via OMIA_ID) - OMIM:257270 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [16]

Horse (Equus caballus) — Osteoporosis (hereditary; OMIA-verified species predisposition)

Disorder: Osteoporosis [62]

Summary: Also known as "bighead" Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1928. 'Bighead' of horses: a heritable disease. Journal of Heredity — OMIA Phene_Article / Article - 1947. Osteoporosis in horses. Indian Vet J — PubMed:PMID20295903 — OMIA Phene_Article / Article - 1928. 'Bighead' of horses: a heritable disease. Journal of Heredity — OMIA Phene_Article / Article - 1947. Osteoporosis in horses. Indian Vet J — PubMed:PMID20295903 — OMIA Phene_Article / Article [62]

Horse (Equus caballus) — Overo lethal white foal syndrome; frame overo spotting (hereditary; OMIA-verified species predisposition)

Mode of inheritance: The Overo coat colour is dominant to normal solid colour, but lethal white foal syndrome (LWFS) is recessive (i.e. the only horses to show this disorder are homozygotes for the Overo allele). [11]

Prevalence: Badial et al. (2018) "developed and validated a high-resolution melting (HRM) genotyping assay to detect the OLWFS causative mutation, and... also determined the frequency of heterozygotes among American Paint horses in Brazil.... The overall estimated frequency of heterozygotes was 21.6%; however, this frequency increased to 89.5% when considering only overo horses". Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Associated gene(s) - Gene: Entrez Gene ID 4143446 (no symbol in OMIA GeneSynonym) — OMIA Phene_Gene - OMIA molecular-genetics note: Noting that mutations in the genes for endothelin 3 (EDN3) or its receptor (EDNRB) are responsible for similar disorders in humans and rodents, Santschi et al. (1998), from the University of Minnesota, sequenced cDNA from 22 affected foals, their parents, and some solid-colour normal controls, all registered with the American Paint Horse Association. There was no variation in the EDN3 gene, but a … Evidence (references) - 1990. Overo Lethal White Foal Syndrome - Equine Model of Aganglionic Megacolon (Hirschsprung Disease). American Journal of Medical Genetics — PubMed:PMID2363434 | DOI:10.1002/ajmg.1320360319 — OMIA Phene_Article / Article - 1987. Current research topics in equine genetics, Part 1. Equine Practice — OMIA Phene_Article / Article - 1990. Megacolon in 2 Related Clydesdale Foals. Australian Veterinary Journal — PubMed:PMID2076076 — OMIA Phene_Article / Article - 1994. Dominant inheritance of overo spotting in paint horses. Journal of Heredity — PubMed:PMID8014463 — OMIA Phene_Article / Article - 1995. Overo spotting in horses. Journal of Equine Veterinary Science — OMIA Phene_Article / Article - 1998. Endothelin receptor B mutation associated with lethal white foal syndrome in horses [abstract]. Plant & Animal Genome VI — OMIA Phene_Article / Article - 1998. Endothelin receptor B polymorphism associated with lethal white foal syndrome in horses. Mammalian Genome — PubMed:PMID9530628 — OMIA Phene_Article / Article - 1982. Ileocolonic aganglionosis in white progeny of overo spotted horses. Journal of the American Veterinary Medicine Association — OMIA Phene_Article / Article - 1998. A missense mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome - an equine version of Hirschsprung-disease. Mammalian Genome — PubMed:PMID9585428 — OMIA Phene_Article / Article - 1998. A dinucleotide mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome (LWFS) - a horse variant of Hirschsprung-disease (HSCR). Human Molecular Genetics — PubMed:PMID9580670 — OMIA Phene_Article / Article - 1983. Congenital intestinal megacolon in white foals. Veterinary Pathology — PubMed:PMID6849219 — OMIA Phene_Article / Article - 2001. Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. American Journal of Veterinary Research — PubMed:PMID11197568 — OMIA Phene_Article / Article - (22 additional references in OMIA) Comparative medicine (human OMIM) - OMIM:600155 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:277580 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:600501 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:131244 (type: gene) — OMIA Group_OMIM (via OMIA_ID) [11]

Horse (Equus caballus) — Prognathism (hereditary; OMIA-verified species predisposition)

Disorder: Prognathism [63]

Summary: see also: OMIA:001271-9796: Dwarfism, ACAN-related in Equus caballus (horse) Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2014. A chromosomal region on ECA13 is associated with maxillary prognathism in horses. PLoS One — PubMed:PMID24466169 | DOI:10.1371/journal.pone.0086607 — OMIA Phene_Article / Article - 2007. Erhebung der Prävalenz von Erbkrankheiten bei dreijährigen Schweizer Warmblutpferden [Prevalence of hereditary diseases in three-year-old Swiss Warmblood horses]. Schweiz Arch Tierheilkd — OMIA Phene_Article / Article - 2007. Erhebung der Prävalenz von Erbkrankheiten bei dreijährigen Pferden der Freiberger-Rasse. [Prevalence of hereditary diseases in three-year-old franches-montagnes horses]. Schweiz Arch Tierheilkd — OMIA Phene_Article / Article - 2017. Heritabilities of health traits in Swiss Warmblood horses. Equine Vet J — PubMed:PMID26538098 | DOI:10.1111/evj.12537 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Genetic factors underlying mandibular prognathism: insights from recent human and animal studies. Mamm Genome — PubMed:PMID39607497 | DOI:10.1007/s00335-024-10084-x — OMIA Phene_Article / Article - 2014. A chromosomal region on ECA13 is associated with maxillary prognathism in horses. PLoS One — PubMed:PMID24466169 | DOI:10.1371/journal.pone.0086607 — OMIA Phene_Article / Article - 2007. Erhebung der Prävalenz von Erbkrankheiten bei dreijährigen Schweizer Warmblutpferden [Prevalence of hereditary diseases in three-year-old Swiss Warmblood horses]. Schweiz Arch Tierheilkd — OMIA Phene_Article / Article - 2007. Erhebung der Prävalenz von Erbkrankheiten bei dreijährigen Pferden der Freiberger-Rasse. [Prevalence of hereditary diseases in three-year-old franches-montagnes horses]. Schweiz Arch Tierheilkd — OMIA Phene_Article / Article - 2017. Heritabilities of health traits in Swiss Warmblood horses. Equine Vet J — PubMed:PMID26538098 | DOI:10.1111/evj.12537 — OMIA Phene_Article / Article - 2024. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep — PubMed:PMID38600096 | DOI:10.1038/s41598-024-57872-8 — OMIA Phene_Article / Article - 2024. Genetic factors underlying mandibular prognathism: insights from recent human and animal studies. Mamm Genome — PubMed:PMID39607497 | DOI:10.1007/s00335-024-10084-x — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:176700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:176700 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [63]

Horse (Equus caballus) — Shivering (hereditary; OMIA-verified species predisposition)

Disorder: Shivering [64]

Summary: Valberg et al. (2023): "Shivers in horses is characterized by abnormal hindlimb movement when walking backward and is proposed to be caused by a Purkinje cell (PC) axonopathy based on histopathology.. Differences in gene expression between Shivers and control horses were evident in principal component analysis of axon-containing white matter but not PC soma.. Our findings support axonal degeneration as a characteristic feature of Shivers." Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1999. Clinical and pathologic findings in two draft horses with progressive muscle atrophy, neuromuscular weakness, and abnormal gait characteristic of shivers syndrome. Journal of the American Veterinary Medical Association — PubMed:PMID14567431 — OMIA Phene_Article / Article - 1955. Lumbar lameness caused by inherited muscle atrophy inhorse. Journal of the Japanese Veterinary Medical Association — OMIA Phene_Article / Article - 2013. Genome-wide association analysis of Shivers in Belgian horses. Equine Genome Workshop, Plan and Animal Genome XXI, San Diego, CA — OMIA Phene_Article / Article - 2015. The equine movement disorder "Shivers" is associated with selective cerebellar Purkinje cell axonal degeneration. Vet Pathol — PubMed:PMID25714471 | DOI:10.1177/0300985815571668 — OMIA Phene_Article / Article - 2018. Abnormal locomotor muscle recruitment activity is present in horses with shivering and Purkinje cell distal axonopathy. Equine Vet J — PubMed:PMID29356055 | DOI:10.1111/evj.12813 — OMIA Phene_Article / Article - 2022. Shivering and Stringhalt in horses. Vet J — PubMed:PMID35462036 | DOI:10.1016/j.tvjl.2022.105829 — OMIA Phene_Article / Article - 2023. Cerebellar axonopathy in Shivers horses identified by spatial transcriptomic and proteomic analyses. J Vet Intern Med — PubMed:PMID37288990 | DOI:10.1111/jvim.16784 — OMIA Phene_Article / Article - 1999. Clinical and pathologic findings in two draft horses with progressive muscle atrophy, neuromuscular weakness, and abnormal gait characteristic of shivers syndrome. Journal of the American Veterinary Medical Association — PubMed:PMID14567431 — OMIA Phene_Article / Article - 1955. Lumbar lameness caused by inherited muscle atrophy inhorse. Journal of the Japanese Veterinary Medical Association — OMIA Phene_Article / Article - 2013. Genome-wide association analysis of Shivers in Belgian horses. Equine Genome Workshop, Plan and Animal Genome XXI, San Diego, CA — OMIA Phene_Article / Article - 2015. The equine movement disorder "Shivers" is associated with selective cerebellar Purkinje cell axonal degeneration. Vet Pathol — PubMed:PMID25714471 | DOI:10.1177/0300985815571668 — OMIA Phene_Article / Article - 2018. Abnormal locomotor muscle recruitment activity is present in horses with shivering and Purkinje cell distal axonopathy. Equine Vet J — PubMed:PMID29356055 | DOI:10.1111/evj.12813 — OMIA Phene_Article / Article - 2022. Shivering and Stringhalt in horses. Vet J — PubMed:PMID35462036 | DOI:10.1016/j.tvjl.2022.105829 — OMIA Phene_Article / Article - 2023. Cerebellar axonopathy in Shivers horses identified by spatial transcriptomic and proteomic analyses. J Vet Intern Med — PubMed:PMID37288990 | DOI:10.1111/jvim.16784 — OMIA Phene_Article / Article [64]

Mule (Equus asinus x caballus) — Alloimmune haemolytic anaemia of the newborn (hereditary; OMIA-verified species predisposition)

Species: Mule (Equus asinus x caballus) [65]

Disorder: Alloimmune haemolytic anaemia of the newborn [65]

Summary: Changed from OMIA000028-37965 (hybrid) to OMIA000028-319699 (Equus asinus × Equus caballus (mule)) [20/09/2023] Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1995. Neonatal isoerythrolysis in mule foals. Journal of the American Veterinary Medical Association — PubMed:PMID7744666 — OMIA Phene_Article / Article - 2024. Alloimmune conditions in the neonatal foal. Vet Clin North Am Equine Pract — PubMed:PMID38852013 | DOI:10.1016/j.cveq.2024.05.001 — OMIA Phene_Article / Article - 1995. Neonatal isoerythrolysis in mule foals. Journal of the American Veterinary Medical Association — PubMed:PMID7744666 — OMIA Phene_Article / Article - 2024. Alloimmune conditions in the neonatal foal. Vet Clin North Am Equine Pract — PubMed:PMID38852013 | DOI:10.1016/j.cveq.2024.05.001 — OMIA Phene_Article / Article [65]

Mule (Equus asinus x caballus) — Polysaccharide storage myopathy/PSSM1/Exertional rhabdomyolysis (hereditary; OMIA-verified species predisposition)

Disorder: Polysaccharide storage myopathy/PSSM1/Exertional rhabdomyolysis [66]

Summary: See ' OMIA:001158-9796: Polysaccharide storage myopathy/PSSM1/Exertional rhabdomyolysis in Equus caballus (horse)' for details. Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 2001. Incidence of polysaccharide storage myopathy in draft horse-related breeds: a necropsy study of 37 horses and a mule. J Vet Diagn Invest — PubMed:PMID11243365 | DOI:10.1177/104063870101300112 — OMIA Phene_Article / Article - 2001. Incidence of polysaccharide storage myopathy in draft horse-related breeds: a necropsy study of 37 horses and a mule. J Vet Diagn Invest — PubMed:PMID11243365 | DOI:10.1177/104063870101300112 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:611556 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:611556 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [66]

Mule (Equus asinus x caballus) — Sarcoid (hereditary; OMIA-verified species predisposition)

Disorder: Sarcoid [67]

Summary: Changed from OMIA000888-37965 (hybrid) to OMIA000888-319699 (Equus asinus × Equus caballus) [20/09/2023] Derived from OMIA database dump (omia.xml, local); structured fields — each value is verbatim from the disorder's source file pdf-raw/omia/<phene_id>.txt: Evidence (references) - 1997. Carbon dioxide laser as a surgical instrument for sarcoid therapy--a retrospective study on 60 cases. Can Vet J — PubMed:PMID9426943 — OMIA Phene_Article / Article - 1997. Carbon dioxide laser as a surgical instrument for sarcoid therapy--a retrospective study on 60 cases. Can Vet J — PubMed:PMID9426943 — OMIA Phene_Article / Article Comparative medicine (human OMIM) - OMIM:181000 (type: trait) — OMIA Group_OMIM (via OMIA_ID) - OMIM:181000 (type: trait) — OMIA Group_OMIM (via OMIA_ID) [67]

Appendix A — Commercial Food & Regulatory Notes

How pet-food regulatory standards treat this species (reference material, demoted from the main flow).

Exotic / specialty pet food — AAFCO recognizes no nutrient profiles for exotics; standards defer to NRC species reports

As an AAFCO-recognized nutrient profile or nutritional authority: [68]

For dogs, the AAFCO Dog Food Nutrient Profiles; [68]

For cats, the AAFCO Cat Food Nutrient Profiles; [68]

For specialty pets, the nutrient recommendations approved by the Committee on Animal Nutrition of the National Research Council of the National Academy of Sciences [68]

Appendix B — Research Evidence

Peer-reviewed papers indexed for this species (reference material). Entries whose abstract did not mention the species by name, or were flagged off-topic at source, were omitted as likely mis-clustered.

Evidence cluster — equine gastric ulcer syndrome: prophylaxis & omeprazole (peer-reviewed, Europe PMC)

PMID 42375980 — [Paraphrased derived summary — non-Open-Access source.] A study background states equine gastric ulcer syndrome (EGUS) is the most common disease of the equine stomach. (Source excerpt truncated to the background sentence only.) [69]

PMID 41470044 — [Paraphrased derived summary — non-Open-Access source.] A study background notes that recurrence of equine squamous gastric disease (ESGD) and equine gastric glandular disease (EGGD) is high once pharmacological treatment is stopped. (Source excerpt truncated to the background sentence only.) [70]

PMID 42076700 — Equine Gastric Ulcer Syndrome is a highly prevalent condition, yet its clinical diagnosis remains challenging due to the nonspecific nature of many associated signs. [CC BY — Open Access, verbatim with attribution.] [71]

PMID PPR1037834 — The term Equine Gastric Ulcer Syndrome (EGUS) has been used since 1999. [69]

PMID 41600665 — Equine Gastric Ulcer Syndrome (EGUS) is a worldwide disease described in different categories of animals. [CC BY — Open Access, verbatim with attribution.] [72]

PMID PPR1037834 (2025, ) — The Current Status of Equine Gastric Ulcer Syndrome in Horses - Focusing on Diagnosis, Treatment and Prevention [69]

PMID 41532453 (2026, Equine veterinary journal) — [Paraphrased derived summary — non-Open-Access source.] A study background notes current EGUS treatments such as omeprazole (a proton-pump inhibitor) have limitations, including the requirement to administer on an empty stomach. (Source excerpt truncated to the background sentence only.) [73]

Horse — anhydrosis / heat & electrolyte management — dietary management (Europe PMC)

PMID 41521281 — Review: Genomic insights into the adaptive traits and stress resistance in modern horses. (Stress biology, 2026). (opening): The domestication and selective breeding of horses have profoundly influenced the emergence of adaptive traits and stress resistance mechanisms, shaping modern equine populations. [74]

PMID 42328694 — Integrative Advances in Equine Genomics From Reference Assemblies to Evolutionary History and Key Traits. (Evolutionary applications, 2026). (opening): Horses are major domestic animals and cultural symbols that have accompanied humans for millennia. They underpin transport, agriculture, warfare and sport, and also provide a model [75]

PMID 42071996 — Efficacy of an Oral Chondroprotective Joint Supplement on Stride Length and Gait Symmetry in Aged Geldings with Chronic Lameness. (Animals: an open access journal from MDPI, 2026). (opening): Oral joint supplements (OJSs), specifically those containing glucosamine and chondroitin sulfate, are some of the most popular feed additives fed by horse owners. However, evidence [76]

PMID 41893540 — The Dark Side of Grasslands: Endophyte Toxicosis in Horses-Exposure Risks, Health Consequences, and Management. (Toxins, 2026). (opening): Grasslands are the cornerstone of horse feeding, used for grazing and to produce roughages and their products. However, improper grassland management hides several threats for equi [77]

Horse — colitis / enteritis — dietary management (Europe PMC)

PMID 41375540 — The Role of Short-Chain Fatty Acids (SCFAs) in Colic and Anti-Inflammatory Pathways in Horses. (Animals: an open access journal from MDPI, 2025). (opening): Equine colic remains a prevalent and potentially life-threatening condition with multifactorial origins, including dietary imbalances, stress, and microbial dysbiosis. Central to e [78]

PMID 41070119 — Gut microbiome regulation in equine animals: current understanding and future perspectives. (Frontiers in microbiology, 2025). (opening): The equine intestinal microbiome represents a complex and dynamic ecosystem that fundamentally influences host health and physiological function. This microbial community exhibits [79]

PMID 42193750 — Long-Read Sequencing for Species-Level Resolution of the Equine Gut Microbiota Reveals the Need for Improved Databases. (Animals: an open access journal from MDPI, 2026). (opening): Differences in gut microbiota composition related to diet have been reported in horses, but characterization of specific microbial taxa remains limited, particularly at the species [80]

PMID 41504615 — Complete Extruded Diet: How Does Equine Fecal Microbiota Change During Intake Adaptation? (Animal science journal = Nihon chikusan Gakkaiho, 2026). (opening): This study aimed to investigate the gradual adaptation of the fecal bacterial community and in vitro fermentative capacity of horses fed a complete extruded diet (CED). Twelve geld [81]

PMID 42046684 — Synergistic effects of (Veterinary world, 2026). (opening): The equine hindgut depends on microbial fermentation for efficient nutrient utilization but remains vulnerable to dysbiosis, hindgut acidosis, and suboptimal fiber digestion. Growi [82]

Horse — recurrent uveitis / ocular health — dietary management (Europe PMC)

PMID 41518147 — Evaluation of Laboratory Techniques for the Diagnosis of Leptospira-Associated Equine Recurrent Uveitis (ERU) With Focus on the Goldmann-Witmer Coefficient. (Veterinary ophthalmology, 2026). (opening): To evaluate different laboratory procedures for determining the etiologic diagnosis of equine recurrent uveitis regarding intraocular infection with Leptospira spp. and to establis [83]

PMID 42278060 — The Role of Omega-3 Fatty Acids in Horses' Nutrition-A Review. (Animals: an open access journal from MDPI, 2026). (opening): This narrative review presents examples of omega-3 fatty acids supplementation in horse nutrition. Fats are essential in equine nutrition, serving not only as an energy source but [84]

Pet horse — pituitary pars intermedia dysfunction (equine Cushing) — diet & nutrition (Europe PMC)

PMID 40872730 — Equine Pituitary Pars Intermedia Dysfunction. (Veterinary sciences, 2025). (opening): Pituitary pars intermedia dysfunction (PPID) is a common, slowly progressive, neurodegenerative disorder of the older horse. Oxidative damage to the hypothalamic periventricular ne [85]

PMID 41742515 — Assessment of baseline adrenocorticotropic hormone and insulin concentrations in healthy horses in Saskatchewan over a 1-year period. (Journal of veterinary internal medicine, 2026). (opening): Endocrine disorders in horses, such as pituitary pars intermedia dysfunction and equine metabolic syndrome, rely on hormone testing for diagnosis, but seasonal and regional variabi [86]

PMID 42193726 — Welfare Assessment in Equine-Assisted Service (EAS) Horses. (Animals: an open access journal from MDPI, 2026). (opening): Equine-Assisted Service (EAS) horses can be exposed to stressors that affect their behavior and welfare. Previous studies investigated behavioral and physiological indicators (PI) [87]

Sport / athletic / performance horse — diet & nutrition management (Europe PMC)

PMID 42278037 — Industry Perceptions of Thoroughbred Racehorse Emotions and Quality of Life: Implications for the Development of an Equine Quality of Life Assessment Tool. (Animals: an open access journal from MDPI, 2026). (opening): Understanding how horses experience their lives is essential for improving their welfare, particularly in high-performance industries such as horseracing. Quality of Life (QoL) fra [88]

PMID 42028318 — Opportunities for agency in domestic horses: Applying the behavioural domain to increase equine welfare. (Animal welfare (South Mimms, England), 2026). (opening): Giving animals the opportunity to exercise agency can improve their welfare, but horse owners and researchers may not be aware of the growing body of agency research in other anima [89]

PMID 42238714 — Genetic variability and associations of Trakehner and other horse populations in Lithuania. (Archives animal breeding, 2026). (opening): To obtain genetic parameters relevant for the management of animal genetic resources, this study provides a comparative characterization of the Trakehner (TRAK) horse population in [90]

References

[1] https://www.gov.uk/government/publications/code-of-practice-for-the-welfare-of-horses-ponies-donkeys-and-their-hybrids

grade A: T1 government/standard, verbatim (computed per docs/topic_grading_guide.md §4)

[2] https://omia.org/OMIA000181/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[3] https://omia.org/OMIA002096/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[4] https://omia.org/OMIA002139/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[5] https://omia.org/OMIA001438/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[6] https://omia.org/OMIA000214/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[7] https://omia.org/OMIA000245/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[8] https://omia.org/OMIA001158/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[9] https://omia.org/OMIA000420/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[10] https://omia.org/OMIA000715/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[11] https://omia.org/OMIA000629/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[12] https://omia.org/OMIA001344/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[13] https://omia.org/OMIA000209/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[14] https://omia.org/OMIA001688/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[15] https://omia.org/OMIA001677/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[16] https://omia.org/OMIA002692/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[17] https://omia.org/OMIA001199/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[18] https://omia.org/OMIA001972/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[19] https://omia.org/OMIA001715/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[20] https://omia.org/OMIA000735/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[21] https://omia.org/OMIA000621/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[22] https://omia.org/OMIA000175/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[23] https://omia.org/OMIA002330/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[24] https://omia.org/OMIA000220/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[25] https://omia.org/OMIA003039/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[26] https://omia.org/OMIA000487/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[27] https://omia.org/OMIA001678/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[28] https://omia.org/OMIA002141/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[29] https://omia.org/OMIA001163/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[30] https://omia.org/OMIA001897/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[31] https://omia.org/OMIA001578/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[32] https://omia.org/OMIA001938/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[33] https://omia.org/OMIA002977/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[34] https://omia.org/OMIA002500/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[35] https://omia.org/OMIA002068/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[36] https://omia.org/OMIA002280/9940/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[37] https://omia.org/OMIA000733/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[38] https://omia.org/OMIA001271/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[39] https://omia.org/OMIA000698/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[40] https://omia.org/OMIA001216/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[41] https://omia.org/OMIA001000/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[42] https://omia.org/OMIA002124/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[43] https://omia.org/OMIA000689/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[44] https://omia.org/OMIA001916/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[45] https://omia.org/OMIA002472/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[46] https://omia.org/OMIA002846/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[47] https://omia.org/OMIA000366/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[48] https://omia.org/OMIA000785/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[49] https://omia.org/OMIA001899/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[50] https://omia.org/OMIA002197/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[51] https://omia.org/OMIA002013/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[52] https://omia.org/OMIA002458/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[53] https://omia.org/OMIA001982/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[54] https://omia.org/OMIA002480/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[55] https://omia.org/OMIA001356/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[56] https://omia.org/OMIA001225/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[57] https://omia.org/OMIA001501/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[58] https://omia.org/OMIA002354/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[59] https://omia.org/OMIA002231/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[60] https://omia.org/OMIA001898/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[61] https://omia.org/OMIA001457/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[62] https://omia.org/OMIA000105/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[63] https://omia.org/OMIA000823/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[64] https://omia.org/OMIA000676/9796/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[65] https://omia.org/OMIA000028/319699/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[66] https://omia.org/OMIA001158/319699/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[67] https://omia.org/OMIA000888/319699/

grade pending: ungraded, verbatim (computed per docs/topic_grading_guide.md §4)

[68] AAFCO — Dog / Cat / Specialty-Pet Food Nutrient Profiles (NRC for specialty pets) — https://www.aafco.org/

grade A: T1 government/standard, verbatim (computed per docs/topic_grading_guide.md §4)

[69] https://pubmed.ncbi.nlm.nih.gov/42375980/

grade B: T2 peer-reviewed, paraphrase (computed per docs/topic_grading_guide.md §4)

[70] https://pubmed.ncbi.nlm.nih.gov/41470044/

grade B: T2 peer-reviewed, paraphrase (computed per docs/topic_grading_guide.md §4)

[71] https://pubmed.ncbi.nlm.nih.gov/42076700/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[72] https://pubmed.ncbi.nlm.nih.gov/41600665/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[73] https://pubmed.ncbi.nlm.nih.gov/41532453/

grade B: T2 peer-reviewed, paraphrase (computed per docs/topic_grading_guide.md §4)

[74] https://pubmed.ncbi.nlm.nih.gov/41521281/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[75] https://pubmed.ncbi.nlm.nih.gov/42328694/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[76] https://pubmed.ncbi.nlm.nih.gov/42071996/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[77] https://pubmed.ncbi.nlm.nih.gov/41893540/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[78] https://pubmed.ncbi.nlm.nih.gov/41375540/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[79] https://pubmed.ncbi.nlm.nih.gov/41070119/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[80] https://pubmed.ncbi.nlm.nih.gov/42193750/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[81] https://pubmed.ncbi.nlm.nih.gov/41504615/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[82] https://pubmed.ncbi.nlm.nih.gov/42046684/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[83] https://pubmed.ncbi.nlm.nih.gov/41518147/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[84] https://pubmed.ncbi.nlm.nih.gov/42278060/

grade A: T2 peer-reviewed, paraphrase/verbatim (computed per docs/topic_grading_guide.md §4)

[85] https://pubmed.ncbi.nlm.nih.gov/40872730/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[86] https://pubmed.ncbi.nlm.nih.gov/41742515/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[87] https://pubmed.ncbi.nlm.nih.gov/42193726/

grade B: T2 peer-reviewed, paraphrase (computed per docs/topic_grading_guide.md §4)

[88] https://pubmed.ncbi.nlm.nih.gov/42278037/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[89] https://pubmed.ncbi.nlm.nih.gov/42028318/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

[90] https://pubmed.ncbi.nlm.nih.gov/42238714/

grade A: T2 peer-reviewed, verbatim (computed per docs/topic_grading_guide.md §4)

Supplement Data Roadmap

Known gaps in this manual, machine-checked against the published text on every build; an item appears only while the gap is still real.

• Root-domain reference(s): https://www.aafco.org/ — these point to a source home page rather than the exact page; being fixed.

Authored by codebuddy · Every statement quoted verbatim from its cited source. Updated 2026-08-24. · Markdown