Hereditary Equine Regional Dermal Asthenia (HERDA Horse)

• 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).

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.

Genotype

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.