Comparative diagnostic challenges in two horses with skin fragility disorders

Summary Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive connective tissue disorder of horses caused by a missense mutation (c.115G>A) in the peptidyl‐prolyl cis–trans isomerase B ( PPIB ) gene, resulting in defective collagen organisation. Clinically and histopathologically, HERDA may resemble other inherited connective tissue disorders, including Ehlers–Danlos syndrome‐like conditions, making definitive diagnosis challenging. This report describes two horses presenting with skin fragility disorders. Both animals underwent clinical examination, skin biopsy with histopathological evaluation and molecular analysis of the PPIB gene. Histopathological examination revealed comparable dermal collagen abnormalities in both horses, including collagen fibre disorganisation and fragmentation. Molecular testing identified homozygosity for the PPIB c.115G>A mutation in one horse, confirming HERDA, whereas the second horse lacked the mutation, supporting an Ehlers–Danlos syndrome‐like phenotype. These findings demonstrate that histopathology alone is insufficient to definitively diagnose HERDA and that molecular testing is essential to distinguish true HERDA from other inherited skin fragility disorders in horses. Accurate genetic diagnosis is critical for appropriate clinical management, breeding decisions and improved understanding of inherited connective tissue disorders affecting horses.