Hereditary Equine Regional Dermal Asthenia, HERDA

(Ehlers-Danlos syndrome)

 

Gene: PPIB

Transmission: Autosomal recessive

For an autosomal recessive genetic disease an animal must have two copies of the mutation in question to be at risk of developing the disease.  Both parents of an affected animal must be carriers of at least one copy of the mutation.  Animals that have only one copy of the mutation are not at risk of developing the disease but are carrier animals that can pass the mutation on to future generations.

Mutation: Substitution, PPIB gene; c.115 G>A, exon1

Breed: Quarter Horse, American Paint Horse, Appaloosa

Age of onset of symptoms: About 1 1/2 years

HERDA (Hereditary Equine Regional Dermal Asthenia) is a genetic disease that affects connective tissue, forming skin that is very fragile. The mutation affects the PPIB gene which in turn results in the synthesis of a defective collagen protein.  Collagen is important for the function of bones, connective tissue and the skin.  In animals affected by HERDA the skin is loose, hyperelastic, fragile and not well attached to underlying tissues.  The first clinical signs appear around 1 and a half years of age and present as skin lesions following abrasions especially in the area of the saddle.  Lesions have difficulty healing.  There is no treatment and severe cases are often euthanized for humanitarian reasons.  The frequency of heterozygous horses for HERDA is 1.8 to 6.5% among Quarter Horses.

 

References:

OMIA link: [0327-9796]

Patterson Rosa L, Troop, TW, Martin K, et al. (2021) Hereditary Equine Regional Dermal Asthenia homozygote adult working horse with mild signs – A Case Report. J Equine Vet Sci 106:103756.  [pubmed/34670706]

Vroman R, Malfait AM, Miller RE, et al. (2021) Animal models of Ehlers-Danlos syndromes: Phenotype, pathogenesis, and translational potential. Front Genet 12:726474.  [pubmed/34712265]

Walker NL,  Patout AR, Cater M. (2020) Industry Perceptions of HERDA in Performance Horses. J Environ Manage. 269:110810. [pubmed/32303321]

Brinkman EL, Weed BC, Patnaik SS,  et al. (2017) Cardiac Findings in Quarter Horses With Heritable Equine Regional Dermal Asthenia. J Equine Vet Sci. 88:102939. [pubmed/28207320]

Badial PR, Oliveira-Filho JP, Winand NJ, Borges AS. (2014) Allele frequency of hereditary equine regional dermal asthenia in American Quarter horses in Brazil determined by quantitative real-time PCR with high resolution melting analysis. Vet J. 199(2):306-7. [pubmed/24355815]

Halper J. (2014) Connective Tissue Disorders in Domestic Animals. Adv Exp Med Biol. 802:231-40.  [pubmed/24443030]

White SD, Bourdeau P. (2011) Prevalence of the mutation in cyclophilin B (PPIB), a causal candidate gene for HERDA, among Quarter Horses in France.  Veterinary Dermatology 22:206-208. [pubmed/21118319]

Tyron RC, White SD, Bannasch DL. (2007) Homozygosity mapping approach identifies a missense mutation in equine cyclophilin B (PPIB) associated with HERDA in the American Quarter Horse.  Genomics 90:93-102. [pubmed/17498917]