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Hereditary Equine Regional Dermal Asthenia (HERDA)
| Acronym: | HERDA |
| Gene: | PPIB |
| Mutation: | c.115G>A |
| Inheritance: | Autosomal Recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Hereditary equine regional dermal asthenia (HERDA), also known as hyperelastosis cutis (HC) or Ehlers-Danlos syndrome is an inherited disease observed in horses. Horses with HERDA have collagen disorder, characterized by multiple areas of loose, stretchy, hyperextensible skin that is not well attached to the horse. Affected horses develop lacerations, haematomas, and seromas from minor trauma, so they cannot be ridden or shown competitively. HERDA is caused by a genetic mutation in cyclophilin B, a member of the peptidyl-propyl isomerase (PPIB) family of proteins, which have chaperoning functions including proper folding of collagen proteins. The missense mutation in the PPIB gene disrupts collagen folding resulting in mentioned histological characteristics of HERDA.
HERDA is inherited as an autosomal recessive trait, therefore both parents must carry at least one copy of the mutation for a horse to be affected. Horses heterozygous for the mutation appear normal, without signs of the disease. HERDA is present predominately in Quarter Horses and horses of Quarter Horse lineage, with the majority of affected animals from cutting horse lines. The disease is incurable, but early detection by genetic testing can identify horses that are affected or carry the specific mutation, which is critical for the selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Grady, J. G., Elder, S. H., Ryan, P. L., Swiderski, C. E., & Rashmir-Raven, A. M. (2009). Biomechanical and molecular characteristics of hereditary equine regional dermal asthenia in Quarter Horses. Veterinary Dermatology, 20(5-6), 591–599. doi:10.1111/j.1365-3164.2009.00830.x
Rashmir-Raven, A. (2013). Heritable Equine Regional Dermal Asthenia. Veterinary Clinics of North America: Equine Practice, 29(3), 689–702. doi:10.1016/j.cveq.2013.09.001