Hereditary equine regional dermal asthenia in three related Quarter horses in Brazil.

The research discusses about the first reported cases of Hereditary Equine Regional Dermal Asthenia (an inherited connective tissue disorder) in three related Quarter horses in Brazil, detailing their clinical symptoms, histological findings, and possible inheritance pattern.

Objective of the Study

• The study aimed to report and evaluate the first occurrence of Hereditary Equine Regional Dermal Asthenia (HERDA), an inherited connective tissue condition, in three related Quarter horses in Brazil.

Clinical Features

• The affected horses exhibited bilateral asymmetric lesions on their skin, specifically in the trunk and lumbar regions. The skin in these areas was thinner than normal and hyperextensible.
• It was observed that when the skin was handled or touched, it led to a painful response.
• Superficial trauma resulted in skin wounds, indicating the fragility of the horse’s skin.
• In certain areas, the skin had thickened borders and hardened fibrotic masses, also known as pseudotumours.

Histological Findings

• Examination of the skin under a microscope revealed that the collagen fibrils were thinner and smaller than usual.
• The collagen fibers within the middle, adventitial, and deep dermis were loosely arranged.
• Notably, the more standard stains for examining skin tissue, Masson’s trichrome and Calleja, did not detect any abnormality in the collagen and elastic fibers.
• Despite the very marked clinical symptoms, electron microscopy, a further higher-resolution diagnostic tool, also did not reveal any distinct abnormalities.
• Pseudotumours were found to have increased cell proliferation (fibroplasia) and new blood vessel formation (neovascularization).

Inheritance Pattern

• The researchers built a pedigree chart for the affected horses and the pattern was suggestive of an autosomal recessive inheritance type, a feature also indicated by prior research on this disease.

Comparison with Other Regions

• The researchers noted that the clinical and histological features observed in the three Brazilian Quarter horses were similarly seen in horses affected by this condition in the United States.