Hyperelastosis in the Horse

Authors: RASHMIR-RAVEN, A - MISS. STATE UNIV.; WINAND, N - MISS. STATE UNIV.; RYAN, P - MISS. STATE UNIV.; PETER, L - MISS. STATE UNIV.; ELDER, S - MISS. STATE UNIV.; COOLEY, J - MISS. STATE UNIV.; HOPPER, R - MISS. STATE UNIV.; PASQUALI, M - MISS. STATE UNIV.; HILL, A - MISS. STATE UNIV.; REED, R - MISS. STATE UNIV.; GRADY, J - MISS. STATE UNIV.; TIPTON, S - MISS. STATE UNIV.; SWIDERSKI, C - MISS. STATE UNIV.

Submitted to: World Equine Veterinary Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2007
Publication Date: 1/1/2008
Citation: Rashmir-Raven, A., Winand, N., Ryan, P.L., Peter, L., Elder, S., Cooley, J., Hopper, R., Pasquali, M., Hill, A., Reed, R., Grady, J., Tipton, S., Swiderski, C. 2008. Hyperelastosis in the Horse. World Equine Veterinary Association Proceedings, Moscow, Russia, January 28th-February 1, 2008. pp. 473-474. (peer-reviewed)

Interpretive Summary: Equine hyperelastosis cutis, also known as dermatosporaxis and Ehlers-Danlos Syndrome (HERDA), is an autosomal recessive inheritable disease that affects primarily the Quarter Horse breed. It is a debilitating skin disorder that often renders the horse useless for intended athletic pursuits due to the nature of the skin lesions that developed. These studies have endeavored to characterize the nature of the disease through pedigree analysis, thermal imaging and genetic screening of normal, affected and carrier animals in the population. The major finding in these studies is that culling on the basis of genetics alone may inadvertently remove non-affected carriers of the genetic defect from the population. Thus, several criteria should be used before culling that include the use of thermography, which can identify the emergence of lesions and thus enable breeders and veterinarians make a more informed decision.

Technical Abstract: Equine hyperelastosis cutis, also known as dermatosporaxis and Ehlers-Danlos Syndrome (HERDA), is an autosomal recessive inheritable disease and has been reported in Thoroughbreds, Morgans, Haflingers , Hanoverians, a Swiss Warmblood, a mule and several Arabian cross horses in the United Kingdom, United States, Switzerland and Canada. In affected horses, the skin separates between the deep and superficial layers which results in “mushy”, “stretchy”, skin that is not well attached to the horse in multiple areas ranging from the size of a dime to nearly the entire horse. Affected horses can have painful skin sloughing with disfiguring scars. The condition may be apparent at birth but is frequently not noticed until training begins around the age of two, after considerable financial and emotional investment has been made. Treatment which consists of minimizing trauma and restriction from sunlight frequently fails to produce an athletically suitable horse. The heritable nature of the disease makes these horses undesirable for most breeding programs and humane euthanasia is usually the final course of action. The goal of our research program is to better characterize hyperelastosis cutis in horses with an emphasis on disease in the Quarter Horse. We have confirmed that a minimum of 14 of the current top 100 cutting sires in the United States (Equistat, 5-year leading sires, 2007) carry HERDA (N/Hr). Registered progeny of these 14 stallions alone currently account for an additional 4,500 carriers, making this genetic defect widely disseminated. Furthermore, the Equistat data base indicates that 1,450 horses have achieved the top 100 cutting horses between 1985 and 2006. Of these top 1,450 horses, 31 are confirmed HERDA carriers and have produced 12,786 offspring. Using multiple criteria which include DNA test confirmation, thermal imaging of the skin surface to localize lesions, we have identified several mildly affected individuals that compete successfully. This, and the value of the horses involved, suggests that stringent culling of HERDA carriers based solely on the presence of the genetic defect may be inadvisable. DNA testing is now available and should be performed on all Quarter Horses. The prevalence of homozygous individuals capable of competing successfully is not currently known, but raises some question over the fate of individuals testing homozygous for the disease at a young age. Thus, a broad goal of eliminating the genetic defect, once identified, may not be in the best interest of the breed. This highlights the need for a thorough understanding of the disease, DNA testing of individuals at risk and early identification of clinical signs, using thermography, will enable equine veterinarians and horse owners alike to responsibly manage the genetic defect within the population.