Heritability analysis corroborated those conclusions drawn from pedigree analysis and calculated increased inbreeding coefficient values for HERDA horses relative to a random sampling of American Quarter Horses[1].
A unique strategy was used to map the HERDA locus which exploited the dataset available, one which consisted of many affected horses but few relatives and only a single complete full-sib family which segregated for the trait. A genome scan to identify areas of homozygosity common to affected HERDA horses was carried out with the goal of roughly mapping the disease locus. Single nucleotide polymorphisms SNPs were discovered in genes predicted to lie within a 20MB interval surrounding AHT58 and allowed the further reduction of the critical interval to 2.
A SNP within the coding sequence of the cyclophilin B gene, predicted to cause a glycine to arginine missense mutation, segregates with the HERDA phenotype and can be used as a tightly linked marker for identifying carriers and affected horses before they show clinical signs of the disease.
A manuscript describing this work will be submitted in January For the remainder of the grant period, studies will be performed to determine if the SNP in cyclophilin B causes functional changes to the protein.
Additional samples from ancestors of 11 affected horses were obtained from the Veterinary Genetics Lab and used to verify the location of the HERDA locus. In this second phase of mapping, 27 markers covering 5 chromosomes were genotyped in 52 horses and used with the software HOMOZ to calculate LOD scores across each potentially significant chromosome. The remaining samples illustrate the recombination events which have reduced the region of homozygosity to 5MB.
To further minimize the critical interval, SNP markers associated with genes predicted to lie in the region were isolated and developed. Ten genes have been analyzed in this fashion and SNP data has been integrated with microsatellite data, further narrowing the critical interval to 2 MB. Am J Vet Res. Am J Hum Genet ; Genome Res ; Inheritance of hereditary equine regional dermal asthenia in Quarter Horses. Unfortunately there is no known treatment or cure for HERDA, and the majority of horses affected are euthanized within years as their condition worsens and the wounds become unmanageable or fatal.
Given the above summary, can you imagine a horse with HERDA living 8 years before exhibiting mild if any signs at all? Not only that, but an active working ranch and roping horse, both before and after his diagnosis. Etalon researchers, alongside Dr. This horse is being ridden daily as a working ranch horse.
His current owners have known and loved him since he was just a yearling, and finally purchased him as a show horse reined cow horse at the age of 4. He was successful as a show horse and ridden regularly. In November , he was participating in a riding clinic with his current owner and presented with these mild skin lesions see video. The lesions were smaller and less severe than typical in HERDA cases, yet the skin appearance and elasticity were noticeably similar.
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