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Two Copies Of White Coat Allele May Be Lethal In Ponies

The dominant gene responsible for white coats in American Shetland ponies and miniature horses has
been identified, and is likely lethal if inherited from both sire and dam.

Dr. Elizabeth Esdaile and a research team from the University of California Davis Veterinary Genetics
Laboratory screened 19 unregistered Shetland ponies from one ranch for a variety of white pattern
markers.

The researchers found inexplicable coat colors in 14 of the ponies, and began looking for other
dominant white variants. They found that all 14 were heterozygous for the W13 gene. Prior to this
discovery, W13 had only been found in two Quarter Horses-Peruvian Paso crosses and one Australian
miniature horse family.

All ponies with the W13 allele had all-white coats with pink skin phenotype, no matter which other
white spotting variants were present.

The scientists also tested hair samples of 25 miniature horses and five Shetland ponies, each of which
their owners called “white.” Two of the miniature horses were heterozygous for the W13 gene. There
were no homozygous ponies; researchers say that homozygosity is most likely lethal.

The scientists noted that the Shetland ponies that had the W13 allele were not registered, and none of
the registered Shetland ponies had the allele. The team suggested that the unregistered Shetlands may
have some Miniature Horse breeding in their past.

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The researchers said these results highlight the presence of the W13 allele in both Shetland ponies and
the American Miniature Horse, and the importance of testing for the variant since inheriting two copies
of the gene is most likely lethal.

Read the study here.

Horses With Vitiligo May Be More Susceptible To Cancer

Vitiligo is an autoimmune disease that causes patches of skin to lose melanocytes, which give the skin its color. Grey horses are primarily affected by this condition around their eyes, muzzle and anus; vitiligo gives the skin a mottled appearance. Scientists who have identified the genes most likely to cause the disorder say that the same genes may also play a role in melanoma risk.

Humans affected by vitiligo have multiple genes involved in the disease – up to 322 of them. Several of these genes have been shown to be involved in malignant melanoma susceptibility in humans.

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Equine research has not shown what genes cause the disorder in horses. Dr. Thomas Druml and researchers from the University of Veterinary Medicine Vienna, the University of Sydney, the Swedish University of Agricultural Sciences, the Slovak University of Agriculture, and the University of Paris-Saclay used genetic data from 152 Lipizzaners and 104 solid-colored Norikers (an Austrian draft horse) to try to identify the genes involved in the disorder.

The scientists visually inspected study horses for vitiligo and found that 33 of the Lipizzaners (21.7 percent) had the condition. Upon investigation, they found several candidate genes on four chromosomes that seemed to play a role in vitiligo development in grey horses. Four of the genes are associated with the immune system and four play a role in tumor suppression and metastasis, which is how cancer cells spread.

The researchers also found that grey horses with a particular gene mutation (STX17) are more likely to develop melanoma. Melanoma occurs in 46.1 to 50 percent of grey Lipizzaners.

The scientists concluded that a relationship exists between the depigmentation phenotype and melanoma in grey horses. They recommend more gene-specific expression and replication studies be completed on different breeds.

Read the study here.

Is There An Equine Gene For Gentleness?

Japanese researchers have discovered that a serotonin receptor gene may make some horses more laid back than others. Serotonin is a brain chemical which affects both mood and social behavior.

A team of scientists from Kyoto University assessed the tractability of 167 Thoroughbred racehorses at a training center by having their handlers fill out a questionnaire. A genetic analysis was then run on each horse, focusing on a serotonin receptor gene that was associated with anxiety-related traits in other species.

The researchers found a significant association between one variation of the serotonin receptor gene and lower tractability (less easily managed or controlled), specifically in fillies. The team concluded that the gene might play a role in a horse's trainability and its effect may be partially dependent on the horse's gender.

Connemara Ponies At Greater Risk For Ocular Cancer, Study Shows

A genetic risk factor for ocular squamous cell carcinoma that has been identified in Belgian draft horses, Haflingers and Rocky Mountain Horses has been proven to affect three additional breeds: Holsteiners, Belgian Warmbloods and Connemara ponies.

Squamous cell carcinoma is the most common cancer in horses. Drs. Margo Crausaz, Thomas Launois, Kathryn Smith-Fleming, Annette McCoy, Kelly Knickelbein and Rebecca Bellone evaluated three cases of ocular cancer with DNA testing and confirmed that each horse had two copies of the variant gene: one from each parent. The risk allele frequency was highest in Connemara ponies. With this information, the scientists recommend Connemara ponies be DNA tested for the gene to assist in breeding selection and management in an effort to limit the possibility of inheriting a copy of the gene from both sire and dam.

Because Holsteiners and Belgian Warmbloods had lower allele frequencies, the research team recommend that additional warmbloods with cancer be evaluated to determine the importance of genotyping.

Read the study here.