Junctional Epidermolysis Bullosa (JEB2) in Saddlebreds
Junctional epidermolysis bullosa (JEB) is an inherited disease that causes moderate to severe blistering of the skin and mouth epithelia, sloughing of hooves in newborn foals, and skin lesions that develop as the foal ages. This test detects a causal variant specific to Saddlebreds and related breeds.
Phenotype: Junctional epidermolysis bullosa (JEB) is an inherited disease that causes moderate to severe blistering of the skin and mouth epithelia, and sloughing of hooves in newborn foals, and progresses to skin lesions with age. Two causal variants have been identified: one is found in Saddlebreds and related breeds (denoted as J2, Saddlebred variant); and another explains this disease in Belgians and related draft breeds (denoted as J, Belgian variant). It is likely that additional, yet unidentified, variants may exist that explain the JEB phenotype in other breeds.
Breeds appropriate for testing: American Saddlebred, Racking Horse
Explanation of Results:
Horses with N/N genotype will not have junctional epidermolysis bullosa and will not transmit this this JEB variant to their offspring.
Horses with N/J2 genotype will not have junctional epidermolysis bullosa, but are carriers. They may transmit this JEB variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a JEB-affected foal.
Horses with J2/J2 genotype will have junctional epidermolysis bullosa, a fatal condition.
at least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Junctional epidermolysis bullosa (JEB) is an inherited disease that causes moderate to severe blistering of the skin and mouth epithelia, and sloughing of hooves in newborn foals. This condition is also known as red foot disease, and was previously known as epitheliogenesis imperfecta (EI) in American Saddlebred horses. Affected foals are typically born alive, but soon develop skin lesions at pressure points. The condition worsens with time and the foal eventually succumbs to severe infection or has to be euthanized.
Junctional epidermolysis bullosa across species has been associated with variants in three genes (LAMA3, LAMB3, LAMC2) that each encode the three subunits of laminin-5, a glycoprotein vital to the integrity of the skin and mucosa. In horses, variants in LAMA3 and LAMC2 have been shown to result in JEB.
A large deletion in the LAMA3 gene (g.3724_10312del6589) was identified in American Saddlebred Horses; this genetic variant is denoted as J2, Saddlebred variant. This recessively inherited deletion spans several exons in LAMA3 and results in a nonfunctional laminin-5. In American Saddlebred horses, the resultant skin disease was referred to as epitheliogenesis imperfecta (EI) before the causative gene was identified, which then established it as a form of junctional epidermolysis bullosa analogous to Herlitz JEB in humans. The J Saddlebred variant may also be found in Saddlebred-related breeds, such as the Racking Horse.
Two copies of J2 are required to develop junctional epidermolysis bullosa. Since affected animals do not survive to breeding age, JEB foals are produced by matings between carrier animals. The VGL offers diagnostic DNA tests that detect the JEB variants. Breeders can reliably use test results to enhance breeding strategies to avoid producing affected foals. Carriers do not need to be removed from the breeding pool. A successful breeding program can use matings of carriers (N/Js) to non-carriers (N/N) without the worry of producing an affected foal.
This test is specific to Saddlebreds and related breeds. For a test specific to Belgian Draft horses and related breeds, click here.
Normal. Horse does not have the variant associated with junctional epidermolysis bullosa 2 identified in the Saddlebred.
Carrier. Horse has one copy of the variant associated with junctional epidermolysis bullosa 2 identified in the Saddlebred.
Affected. Horse has two copies of the variant associated with junctional epidermolysis bullosa 2 identified in the Saddlebred. Foals will likely develop skin lesions increasing in severity with age that are ultimately fatal.
Spirito, F., Charlesworth, A., Ortonne, J., Meneguzzi, G., Linder, K., & Baird, J. (2002). Animal Models for Skin Blistering Conditions: Absence of Laminin 5 Causes Hereditary Junctional Mechanobullous Disease in the Belgian Horse. Journal of Investigative Dermatology, 119(3), 684-691. doi: 10.1046/j.1523-1747.2002.01852.x
Graves, K.T., Henney, P.J., & Ennis, R.B. 2009. Partial deletion of the LAMA3 gene is responsible for hereditary junctional epidermolysis bullosa in the American Saddlebred Horse. Animal Genetics, 40(1), 35-41. doi: 10.1111/j.1365-2052.2008.01795.x