CHAPTER 154 Hereditary Equine Regional Dermal Asthenia
Hereditary equine regional dermal asthenia (HERDA) or hyperelastosis cutis is an inherited skin disorder seen predominantly in the American Quarter Horse breed. It has also been seen in breeds that share bloodlines with the American Quarter Horse, including American Paint horses and Appaloosas. The disease first manifests in young horses. Previous reports suggested an association between first saddling and the onset of clinical signs; however this may be related to maturation of the skin that corresponds to the age at which horses are broken to ride. Although inherited disorders are often thought to be congenital (present at birth), this is not always the case. There are many examples in other species of adult-onset inherited disorders. In horses specifically, inherited disorders are not as easily recognized, especially ones that do not appear as congenital diseases, because of the nature of horse reproduction. Foals are rarely born as twins, and full siblings are relatively uncommon. The genetic basis of a disease is difficult to distinguish from a birth defect unless full siblings are affected with the same problem. Most of the currently recognized inherited disorders in horses have been established based on breed predispositions to a disease recognized over a relatively long period. HERDA is just such an example. Initial reports of the disease occurred about 30 years ago. Over the course of the last 10 years, we have collected enough data to establish that the disease is inherited and to identify the location of the gene responsible for the disease.
