Breeds Affected: American Saddlebred
Samples Accepted: Blood, Hair
Disease Information: Junctional epidermolysis bullosa is a fatal connective tissue disease, wherein the skin is not properly connected to the underlying tissue. Foals are born looking normal but develop severe skin lesions and hoof wall detachment within days of birth, usually resulting in deadly infections or humane euthanasia.
Inheritance Information: JEB-2 is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The horse is normal, and cannot produce JEB-2-affected offspring.
N/jeb2 The horse is a carrier of JEB-2, and can pass the allele on to approximately 50% of any offspring. If bred to another N/jeb2 carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
jeb2/jeb2 The horse is affected with JEB-2. This disease is fatal, and affected horses do not usually live long enough to reproduce.
– Carriers may be bred to normal animals (N/jeb2 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/jeb2 x N/jeb2) is not recommended due to the possibility of 25% of the offspring being affected.
Test Information: This mutation test is based on a deletion in the LAMA3 gene.
Graves, K. T., Henney, P. J. and 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: 35–41. doi: 10.1111/j.1365-2052.2008.01795.x
Further information is available at the Online Mendelian Inheritance in Animals website.