Biomechanical and molecular characteristics of hereditary equine regional dermal asthenia in Quarter Horses

Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive skin disorder that has yet to be fully characterized. HERDA is predominately expressed in Quarter Horses, with the majority of these disseminating from elite cutting horse bloodlines, leading to the increased incidence of HERDA in recent years. Affected horses have loose, hyper-extensible, fragile skin and are frequently euthanized due to poor wound healing and disfiguring scars. This study sought to better characterize HERDA by analysis of the biomechanical parameters of tensile strength, modulus of elasticity, energy to failure and thickness of skin from 10 affected and 6 unaffected horses using an Instron^® Universal Testing Instrument. In addition, total soluble collagen and glycosaminoglycan concentrations of skin were analysed from 13 affected and 12 unaffected horses using Sircol™ Soluble Collagen and Blyscan™ Sulfated Glycosaminoglycan assays respectively. Affected horses exhibited a two to threefold reduction in tensile strength versus unaffected horses with statistically significant differences at six of seven sample locations (P ≤ 0.05). The modulus of elasticity proved to be significantly different at six of seven sample locations, energy to failure at six of seven sample locations, and skin thickness at one of seven sample locations (P ≤ 0.05). Affected horses exhibited significantly higher amounts of total soluble collagen than unaffected horses (P ≤ 0.05). No significant difference was demonstrated between groups for glycosaminoglycan concentration. Affected horses demonstrated uniformly weaker skin across sample locations, indicating the biomechanical properties of HERDA are not regionally confined to specific areas of the horses' skin.