Dermatological and morphological findings in quarter horses with hereditary equine regional dermal asthenia

Abstract

Background Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive disorder affecting quarter horses (QHs); affected horses exhibit characteristic skin abnormalities related to abnormal collagen biosynthesis.Hypothesis/Objectives To characterize the thickness and morphological abnormalities of the skin of HERDA-affected horses and to determine the interobserver agreement and the diagnostic accuracy of histopathological examination of skin biopsies from horses with HERDA.Animals Six affected QHs, confirmed by DNA testing, from a research herd and five unaffected QHs from a stud farm.Methods The skin thickness in 25 distinct body regions was measured on both sides in all affected and unaffected horses. Histopathological and ultrastructural evaluation of skin biopsies was performed.Results The average skin thickness in all of the evaluated regions was thinner in the affected horses. A statistically significant difference between skin thickness of the affected and unaffected animals was observed only when the average magnitude of difference was 38.7% (P=0.038). The interobserver agreement for the histopathological evaluation was fair to substantial. The histopathological sensitivity for the diagnosis of HERDA was dependent on the evaluator and ranged from 73 to 88%, whereas the specificity was affected by the region sampled and ranged from 35 to 75%.Conclusions and clinical importance Despite the regional pattern of the cutaneous signs, skin with decreased thickness was not regionally distributed in the HERDA-affected horses. Histopathological evaluation is informative but not conclusive for establishing the diagnosis. Samples of skin from the neck, croup or back are useful for diagnosis of HERDA. However, the final diagnosis must be confirmed using molecular testing.