Hereditary Equine Regional Dermal Asthenia (HERDA Horse)
Hereditary Equine Regional Dermal Asthenia (HERDA) is caused by the presence of abnormal collagen in the skin. This results in skin detachment, severe lesions, ulcerations and wound healing problems.
The disease occurs in the Quarter Horse and related breeds. It is inherited autosomal recessively.
Synonym: Ehlers-Danlos syndrome, hyperelastosis cutis
- Loose sloughing skin
- Lesions and ulcerations/cysts especially in dorsal area
- Slow healing
- Hyperelastic skin
- Hereditary Equine Regional Dermal Asthenia (HERDA) is caused by the presence of abnormal collagen in the skin.
- Defect in the connective tissue results in skin splitting, tearing and separating from underlying layers.
- Areas under pressure (saddle, etc.) are particularly affected, and the skin traumas heal very slowly.
- Also known as Ehlers-Danlos Syndrome.
- First symptoms may be seen at the age of 1.5 years.
- Affected horses are usually euthanized due to poor quality of life.
This test detects a single basepair change (c.115G>A) in exon 1 of the Peptidylprolyl Isomerase B gene (PPIB gene or Cyclophilin B).
Genotype and Lab Report
Inheritance: autosomal recessive
→ Only horses with two copies of the variant (herda/herda) are affected. Horses with only one copy (N/herda) are clinically healthy carriers.
N/N = normal
The horse has no copies of the genetic variant causitive for HERDA and therefore cannot pass it on to its offspring.
N/herda = a carrier
The horse is clinically healthy. It has one copy of the genetic variant causitive for HERDA, which will be passed on to its offspring with a probability of 50%.
herda/herda = affected
The horse is affected and has two copies of the genetic variant causitive for HERDA. The variant will be passed on to its offspring with a probability of 100%. All offspring will be carriers.
- Carriers may be bred to normal animals (N/herda x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
- Breeding two carriers (N/herda x N/herda) is not recommended due to the possibility of 25% of the offspring being affected.
- Affected animals (herda/herda) should not be used for breeding.
Bowser, J.E., Elder, S.H., Pasquali, M., Grady, J.G., Rashmir-Raven, A.M., Wills, R., Swiderski, C.E.: Tensile properties in collagen-rich tissues of Quarter Horses with hereditary equine regional dermal asthenia (HERDA). Equine Vet J 46:216-22, 2014. Pubmed reference: 23738970. DOI: 10.1111/evj.12110.
Tryon RC, White SD, Bannasch DL. Homozygosity mapping approach identifies a missense mutation in equine cyclophilin B (PPIB) associated with HERDA in the American Quarter Horse. Genomics. 2007 Jul;90(1):93-102. DOI: 10.1016/j.ygeno.2007.03.009.
Further information is available at Online Mendelian Inheritance in Animals.