Discovered at UC Davis Hereditary Equine Regional Dermal Asthenia (HERDA)

Quick Summary

Hereditary equine regional dermal asthenia (HERDA) is an inherited skin condition primarily found in Quarter Horses that is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses.

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Phenotype: Hereditary equine regional dermal asthenia (HERDA) is an inherited skin disease characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses.

Mode of Inheritance: Autosomal recessive

Alleles: N = Normal/Unaffected, HRD = Hereditary equine regional dermal asthenia

Breeds appropriate for testing: Quarter Horse and related breeds

Explanation of Results:

  • Horses with N/N genotype will not have hereditary equine regional dermal asthenia and cannot transmit this hereditary equine regional dermal asthenia variant to their offspring.
  • Horses with N/HRD genotype will not be affected by hereditary equine regional dermal asthenia, but are carriers. They may transmit this hereditary equine regional dermal asthenia variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing an affected foal.
  • Horses with HRD/HRD genotype will have hereditary equine regional dermal asthenia. 

Turnaround Time
At least 10 business days; may be delayed beyond 10 business days if sample requires additional testing, or a new sample is requested.
Price

$45 one test per animal
+ $15 each additional test from list below:

$100 entire Quarter Horse & Related Breeds Disease Panel (5-panel plus) (all 6 tests)

Order Test

Sample Collection

Horse DNA tests are carried out using cells from the roots of a hair sample (roughly 20-30 hairs).

1. Grab about 10 hairs at the base.

2. Wrap the hairs around your finger and give it a quick pull.

3. Check the ends to make sure the pulled hairs have roots.

4. Repeat the process until you have collected about 20-30 hairs with intact roots.

5. You can choose different places on the mane or tail. NOTE: For foals, we recommend pulling all hairs from the tail only. 

6. Tape the hairs to the submission form and fold the form along the dotted line to protect the sample. Do not use ziploc bags as they can cause condensation that allows mold to grow on the hair.

Hairs with roots

7. Place the folded form containing the sample in a paper envelope and mail it to the laboratory.

 

Additional Details

Hereditary equine regional dermal asthenia (HERDA) is a genetic skin disease predominantly found in the American Quarter Horse. Within the breed, the disease is prevalent in particular lines of cutting horses. HERDA is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses. Affected foals rarely show symptoms at birth. The condition typically occurs by the age of two, most notably when the horse is first being broke to saddle. There is no cure, and the majority of diagnosed horses are euthanized because they are unable to be ridden and are inappropriate for future breeding.

HERDA has an autosomal recessive mode of inheritance and affects stallions and mares in equal proportions. Research carried out in Dr. Danika Bannasch's laboratory at the University of California, Davis, identified the mutation causing HERDA. HERDA is caused by a single base change in the gene PPIB (c.115G>A). This missense mutation codes for a change in the gene product, specifically the normal  glycine at position 39 is changed to an arginine (denoted as p.G39R) altering the Peptidylprolyl Isomerase B (PRIB) protein. PPIB is one of the proteins involved in proper collagen formation. Collagen is is an important structural protein of all connective tissues including skin. Functional studies have shown that the HERDA mutation delays proper collagen folding and secretion and is presumed to alter collagen organization thus leading to the clinical manifestations.

This diagnostic DNA test for HERDA allows identification of horses that are affected or that carry the specific mutation. Other skin conditions can mimic the symptoms of HERDA; this DNA test will assist veterinarians to make the correct diagnosis. For horse breeders, identification of carriers is critical for the selection of mating pairs. Breedings of carrier horses have a 25% chance of producing an affected foal. Breedings between normal and carrier horses will not produce a HERDA foal, although 50% of the foals from this type of cross are expected to be carriers.

Other Resources

UC Davis School of Veterinary Medicine Health Topics

Type of Sample
20-30 Hairs With Roots

Species

Horse

Breed

Appendix Paint Horse Quarter Horse
Type of Test
Health
Results Reported As
Test Result Hereditary Equine Regional Dermal Asthenia (HERDA)
N/N Normal. No copies of the  HERDA allele detected.
N/HRD Carrier. One copy of the HERDA allele detected.
HRD/HRD Affected. Two copies of the HERDA allele detected and horse will develop the disease.
References

White, S.D., Affolter, V.K., Bannasch, D.L., Schultheiss, P.C., Hamar, D.W., Chapman, P.L., Naydan, D., Spier, S.J., Rosychuk, R.A.W., Rees, C., Veneklasen, G.O., Martin, A., Bevier, D., Jackson, H.A., Bettenay, S., Matousek, J., Campbell, K.L., & Ihrke, P.J. (2004). Hereditary equine regional dermal asthenia (‘hyperelastosis cutis’) in 50 horses: clinical, histological, immunohistological and ultrastructural findings. Veterinary Dermatology, 15, 207-217. doi: 10.1111/j.1365-3164.2004.00402.x

Tryon, R. C., White, S. D., & Bannasch, D. L. (2007). Homozygosity mapping approach identifies a missense mutation in equine cyclophilin B (PPIB) associated with HERDA in the American Quarter Horse. Genomics, 90(1), 93-102. doi: 10.1016/j.ygeno.2007.03.009

Tryon, R.C., Penedo, M.C., McCue, M.E., Valberg, S.J., Mickelson, J.R., Famula, T.R., Wagner, M., Jackson, M.A., Hamilton, M.J., Nooteboom, S., & Bannasch, D.L. (2009). Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. Journal of the American Veterinary Medical Association, 234(1), 120-125. doi: 10.2460/javma.234.1.120

Ishikawa, Y., Vranka, J.A., Boudko, S.P., Pokidysheva, E., Mizuno, K., Zientek, K.D., Keene, D.R., Rashmir-Raven, A.M., Nagata, K., Winand, N.J., & Baechinger, H.P. (2012). Mutation in cyclophilin B that causes hyperelastosis cutis in American Quarter Horse does not affect peptidylprolyl cis-trans isomerase activity but shows altered cyclophilin B-protein interactions and affects collagen folding. The Journal of Biological Chemistry, 287(26), 22253-22265. doi: 10.1074/jbc.M111.333336

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

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