Hereditary equine regional dermal asthenia

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Hereditary equine regional dermal asthenia (HERDA) aka hyperelastosis cutis (HC) is an inherited autosomal recessive connective tissue disorder. Affected horses have extremely fragile skin that tears easily and exhibits impaired healing. In horses with HC, the skin separates between the deep and superficial dermis. There is no cure. Most individuals receive an injury they can not heal, and are put down. Managed breeding strategy is currently the only option for reducing the incidence of the disease.

As of May 9, 2007, Researchers working independently at Cornell University and at the University of California, Davis announced that a DNA test for HERDA has been developed. Over 1,500 horses were tested during the development phase of the test, which is now available to the general public through both institutions.^[1]

The disease is found primarily in the American Quarter Horse, specifically in cutting horse lines. Affected horses have been found to trace to the stallion Poco Bueno, or possibly, farther back to one of his ancestors.^[2] Researchers have now named four deceased Quarter Horse stallions that were carriers and produced at least one affacted HERDA foal; they are Dry Doc, Doc O'Lena, Great Pine, and Zippo Pine Bar. These stallions all trace to Poco Bueno through his son and daughter Poco Pine and Poco Lena. Other breeds affected are the American Paint Horse (APHA), and the Appaloosa (ApHC) and any other breed registry that allows outcrossing to AQHA horses.

HERDA is characterized by abnormal skin along the back that tears easily and heals into disfiguring scars. The skin is loose, and hyper-elastic in affected horses. Symptoms typically don’t appear until the horse is subjected to pressure or injury on their back, neck or hips, usually around two yrs of age. However foals can show signs when injured, while other horses mature and only show signs in the joints.^[3] The expression of HERDA is variable, and the phenotypic range of expression is still being determined.