Inheritance of hereditary equine regional dermal asthenia in Quarter Horses

Department of Population Health and Reproduction, University of California, Davis, CA 95616, USA.
American Journal of Veterinary Research (Impact Factor: 1.34). 04/2005; 66(3):437-42. DOI: 10.2460/ajvr.2005.66.437
Source: PubMed


To assess heritability and mode of inheritance for hereditary equine regional dermal asthenia (HERDA) in Quarter Horses.
1,295 horses with Quarter Horse bloodlines, including 58 horses affected with HERDA.
Horses were classified as affected or unaffected or as undetermined when data were insufficient to assess phenotype. Pedigree data were analyzed to determine the probable mode of inheritance. Heritability was estimated by use of Bayesian statistical methods.
Heritability (mean+/-SD) of HERDA was estimated to be 0.38+/-0.13, with both sexes having an equal probability of being affected. Results for evaluation of the pedigrees were consistent with a single Mendelian autosomal recessive mode of inheritance.
HERDA in Quarter Horses is an inherited disease, and affected horses are more likely to produce affected offspring. An autosomal recessive mode of inheritance should be considered by people making breeding decisions involving Quarter Horses when a first-degree relative has been confirmed with HERDA or has produced affected offspring. In addition, breeders whose horses have produced affected offspring can reduce the likelihood of producing affected horses in the future by avoiding inbreeding.

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    • "Although the mouse model recapitulates clinical features of the human disease, the phenotypes observed seem not to provide additional insights into the disease pathogenesis from what is already known of the disease affecting the human yet. Further, a missense G31R mutation in CyPB/PPIB was found in the horse to cause the degenerative skin disorder, HERDA, without changes in skeletal or collagen being reported (Tryon et al., 2005). Hence, additional studies are needed to understand what physiological substrate(s) are directly impaired by the loss of CyPB/PPIB function and promote disease pathogenesis. "
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    • "Hereditary equine regional dermal asthenia is an autosomal recessive dermatological condition of Quarter Horses and related crosses (Tryon et al. 2005). Though in some reports the condition has been referred to as " hyperelastosis cutis', this terminology has been discouraged as the defect does not appear to be in the elastic fibers (White et al. 2004). "
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    • "Diagnosed cases of HERDA and control samples were collected as previously reported [2]. With the permission of the American Quarter Horse Association (AQHA), backlogged hair root samples of relatives of affected horses were made available from the VGL, which conducts parentage testing for all registered American Quarter Horses. "
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    ABSTRACT: Hereditary equine regional dermal asthenia (HERDA), a degenerative skin disease that affects the Quarter Horse breed, was localized to ECA1 by homozygosity mapping. Comparative genomics allowed the development of equine gene-specific markers which were used with a set of affected horses to detect a homozygous, identical-by-descent block spanning approximately 2.5 Mb, suggesting a recent origin for the HERDA mutation. We report a mutation in cyclophilin B (PPIB) as a novel, causal candidate gene for HERDA. A c.115G>A missense mutation in PPIB alters a glycine residue that has been conserved across vertebrates. The mutation was homozygous in 64 affected horses and segregates concordant with inbreeding loops apparent in the genealogy of 11 affected horses. Screening of control Quarter Horses indicates a 3.5% carrier frequency. The development of a test that can detect affected horses prior to development of clinical signs and carriers of HERDA will allow Quarter Horse breeders to eliminate this debilitating disease.
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