Hereditary Equine Regional Dermal Asthenia homozygote adult working horse with mild signs - A Case Report.
Authors: Patterson Rosa Laura, Troop Tyler W, Martin Katie, Vierra Micaela, Foster Gabriel, Lundquist Erica, Brooks Samantha A, Lafayette Christa
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Hereditary Equine Regional Dermal Asthenia (HERDA) is an autosomal recessive condition caused by a mutation in the PPIB gene (which encodes peptidyl-prolyl cis-trans isomerase B) and manifests similarly to Ehlers-Danlos syndrome in humans, resulting in abnormally fragile and hyperelastic skin prone to slow-healing wounds, atrophic scarring, and ulceration—particularly over pressure-bearing areas. This 2021 case report documents an 8-year-old Quarter Horse homozygous for the c.115G>A PPIB missense mutation who presented with notably atypical mild clinical signs, detected only after painful dorsal skin lesions developed during ridden work, prompting genetic testing by the referring veterinarian. Whilst HERDA-affected horses are conventionally considered unrideable and sometimes require euthanasia when wounds become severe, this individual demonstrated sufficient functionality to work under saddle before diagnosis, challenging the assumption that all homozygotes present with uniformly severe disease. The authors highlight that mildly affected individuals may be substantially underdiagnosed because practitioners lack obvious clinical triggers (such as severe non-healing wounds) to recommend genetic testing, suggesting the true prevalence of HERDA may be underestimated in the population. Further investigation into phenotypic heterogeneity and the factors modulating disease severity is warranted to improve case identification and inform management decisions for affected horses.
Read the full abstract on PubMed
Practical Takeaways
- •Consider genetic testing for HERDA in horses with recurrent dorsal skin lesions or slow-healing wounds, even if clinical signs appear mild, as some affected horses may remain functional
- •Not all HERDA-positive horses will be unrideable or require euthanasia; clinical severity varies and mild cases may go undetected without proactive genetic screening
- •Understanding variable disease presentation is important for breeding decisions and owner communication, as homozygous carriers may have different prognoses than traditionally expected
Key Findings
- •An 8-year-old homozygous HERDA horse (c.115G>A PPIB mutation) presented with notably mild clinical signs including only dorsal skin lesions under saddle area, contrary to typical severe presentations
- •Genetic testing revealed HERDA in a previously undiagnosed horse that remained rideable with mild signs, suggesting clinical presentation severity is variable
- •Mildly affected HERDA individuals may be underdiagnosed due to absence of the severe wounds and ulcers that typically prompt genetic testing