Hereditary Equine Regional Dermal Asthenia (HERDA)

HERDA (Hereditary Equine Regional Dermal Asthenia) is an inherited connective tissue disorder affecting primarily Quarter Horses and related breeds. The disease is also known as dermal asthenia or skin hyperelasticity and is characterized by extremely fragile, thin, and easily injured skin. Due to impaired collagen formation, extensive skin tears may occur even after minor mechanical trauma, significantly reducing the quality of life of affected horses.

Symptoms usually begin to appear in young horses after training has started, when the skin is exposed to increased mechanical stress. The skin is thin, fragile, and tears easily. Wounds heal slowly, often resulting in prominent scars, and repeated injuries may lead to chronic skin problems. Due to pain and a poor prognosis, affected horses are often withdrawn from sport and breeding.

HERDA is caused by the c.115G>A mutation in the PPIB gene, which encodes the protein cyclophilin B. This protein is involved in the proper folding and maturation of collagen, the main structural protein of connective tissues. The mutation disrupts the formation of properly functioning collagen fibers, resulting in reduced strength and resilience of the skin.

The mutation is inherited in an autosomal recessive manner. This means that the disease develops only in individuals that inherit the mutated allele from both parents. Carriers of the mutated allele are clinically healthy but can pass the mutation on to their offspring. When two heterozygous carriers are mated, theoretically 25% of the offspring will be clear, 50% will be carriers, and 25% will inherit the mutated allele from both parents and therefore be affected by the disease.

Genetic testing makes it possible to reliably identify carriers of the mutation and prevent the birth of affected foals through appropriate breeding planning.