A team of researchers at Texas A&M University say that a dangerous skin condition affecting quarter horses can affect any breed of horse without genetic links.
Hereditary equine regional dermal asthenia (HERDA; “hyperelastosis cutis”) mainly affects quarter horses, which have a defect in their collagen fibers or in the way those fibers are structurally organized in the mid to deep dermis. In such horses, the skin over the back and sides of the neck is easily torn or stretched, and it often develops seromas and hematomas (“blisters” filled with either serum or blood).
But the researchers found the same condition – Ehlers-Danlos syndrome – can be found in any breed without the familial association typically present with HERDA.
Genetic tests on a gelding presenting with the condition did not find the mutation described in the PPIB gene, previously shown to be associated with HERDA.
Lesions on the horse exhibited either a firm, scar-like appearance or a potential space between the superficial and deep dermis. Both lesioned and non-lesioned skin showed evidence of edema and collagen fragmentation, whereas lesions were also characterized by hemorrhage and inflammation.
Three independent laboratories, each using different methods, did not find mutations in the PPIB gene, either at the known location of the point mutation or at any other location in the coding sequence.
“These findings are suggestive of a diagnosis of HERDA or hyperelastosis cutis in the absence of the well-described, putatively causative mutation in the PPIB gene.
“We propose that, whereas HERDA refers specifically to a familial disease caused by a mutation in the PPIB gene, similar symptoms may in fact be caused by a syndrome resulting from either inherited or spontaneous mutations in any of a number of collagen-processing genes.
“We conclude that Ehlers-Danlos syndrome be diagnosed in horses of any breed with HERDA-like pathology without the causative mutation.”
Ehlers-Danlos Syndrome in a Quarter Horse Gelding: A Case Report of PPIB-Independent Hereditary Equine Regional Dermal Asthenia; Samantha M. Steelman, PhD, Nikki D. Jackson, DVM, Eleanore Conant, PhD, Rytis Juras, PhD, Ernest G. Cothran, PhD, John F. Edwards, DVM, PhD, Bhanu P. Chowdhary, VMD.