Hereditary Equine Regional Dermal Asthenia - History

History

The disease first was recognized in 1971. Research of affected animals indicated that 95% of the identified HERDA horses have traced back to Poco Bueno on both sides of the pedigree. Some also trace to his full brother, Old Grand Dad. The remaining 5% trace to King, the sire of both horses. This may suggest that Poco Bueno could have inherited the HC mutation form his sire, with the possibility that the condition goes even further back. It is difficult to trace the condition further because no pedigrees to date completely distinguish the lines of King.

A disease consistent with HERDA/HC was described in the scientific literature in 1988 documenting two related affected Quarter Horses. Researchers at Mississippi State University described a separation of the upper and lower dermis associated with a loose packing of collagen fibrils in a one year old filly with hyperelastosis cutis. In 2004, clinical veterinarians at the University of California, Davis first coined the term hereditary equine regional dermal asthenia (HERDA) after examining 50 horses with stereotypical presentation of the disease. Shortened and thinned collagen fibrils in the deep dermis was the significant characteristic shared among the affected skin of diseased horses.

Throughout the years, closely breeding back, or inbreeding, to the lines of Poco Bueno increased the frequency of homozygousity in the population, thus increasing the number of affected animals. The 2004 Quarter Horse News Stallion Register revealed that of the top 100 cutting horse stallions, 14 are known HERDA carriers. Today, approximately 28% of all horses of cutting horse bloodlines are carriers of HERDA.

Using DNA from the UC Davis clinical collection of HERDA samples, collaborating UC Davis geneticists searched for discreet areas of DNA that were homozygous, or identical by descent, uniquely in affected horses. UC Davis first reported successful preliminary mapping in January 2004. Additional work verified the disease was inherited, rather than caused solely by environmental insult, and strongly indicated an autosomal recessive mode of inheritance. In January 2007, UC Davis presented their findings at the Plant and Animal Genome Conference Equine Workshop indicating the ability to identify horses that carry HERDA. A full accounting of this work, detailing the mapping and identification of a mutation in cyclophilin B, or peptidyl-prolyl isomerase B (PPIB), was published on May 11, 2007. Concurrent with publication of these results, the Veterinary Genetics Laboratory at UC Davis began offering a genetic test to identify carriers of the disease allele.

In Spring 2007, researchers working independently at Cornell University and at the University of California, Davis announced that a DNA test for HERDA had been developed. Over 1,500 horses were tested during the development phase of the test, which was initially available to the general public through both institutions. A United States patent for the HERDA test was issued to UC Davis on October 27, 2009.