More than just skin deep!!

Hereditary equine regional dermal asthenia (HERDA) belongs to a group of autosomal recessive inheritable connective tissue disorders characterized by a lack of integrity in the epidermis and dermal-epidermal junction that primarily affects the American Quarter Horse. The abnormal collagen production and possible malfunction of the normal inflammatory response system causes the skin along the trunk and lumber region to become loose, hyperextensible and fragile. This results in the outer dermal layer ‘peeling’ away from the deep tissue layers. Handling the skin, either by direct manipulation or the indirect rubbing of a saddle during training, will elicit a painful response and superficial trauma. These large lesions across the dorsum of the horse result in slow healing, hematoma and hygroma formation, thus deeming them unfit for breeding and riding. There is no effective treatment or cure for HERDA and given that the defect cannot be diagnosed with a skin biopsy at birth, horses are usually euthanized upon appearance of clinical signs, typically within the first two to four years of their life.

‘Homozygosity mapping’ by researchers at the University of California has lead to the recent discovery and identification of a gene mutation on chromosome one that is responsible for this collagen defect. During late 2006 and 2007 a DNA diagnostic test was further developed which will allow breeders to identify carriers of HERDA and take responsibility in avoiding the continual production of offspring with this disease. The DNA screening test will also prevent the unnecessary destruction of misdiagnosed horses.

Primary source:
Case report: Hereditary equine regional dermal asthenia in three related Quarter horses in Brazil