Tensile properties in collagen‐rich tissues of Q uarter H orses with hereditary equine regional dermal asthenia ( HERDA )

Summary Reasons for performing study H ereditary equine regional dermal asthenia ( HERDA ) is an autosomal recessive disorder of Q uarter H orses characterised by skin fragility. Horses with HERDA have a missense mutation in peptidyl‐prolyl cis‐trans isomerase  B ( PPIB ), which encodes cyclophilin  B and alters folding and post translational modifications of fibrillar collagen. Objectives The study aimed to test the hypothesis that tendons, ligaments and great vessels, which, like skin, are rich in fibrillar collagen, will also have abnormal biomechanical properties in horses with HERDA . Study design Ex vivo biomechanical study comparing horses with and without a diagnosis of HERDA . Methods Forelimb suspensory ligament, superficial and deep digital flexor tendons; withers, forelimb and abdominal skin; the main pulmonary artery and the aortic arch were harvested from 6 horses with HERDA and 6 control horses without the HERDA allele. Tissues were distracted to failure. Tensile strength ( TS ), elastic modulus ( EM ) and energy to failure ( ETF ) were compared. Results Horses with HERDA had significantly lower TS and EM in tendinoligamentous tissues and great vessels, respectively. The TS , EM and ETF were significantly lower in skin from horses with HERDA . Differences in TS and ETF were more extreme at the withers than at the forelimb or abdomen. Conclusions Tendinoligamentous tissue, great vessels and skin are significantly weaker in horses with HERDA than in horses lacking the PPIB mutation, substantiating that diverse tissues with high fibrillar collagen content are abnormal in HERDA and that the HERDA phenotype is not limited to the integument.