JEB2 in American Saddlebreds: Understanding Junctional Epidermolysis Bullosa & LAMA3 Mutation

Junctional Epidermolysis Bullosa 2 (JEB2), also known as red foot disease or hairless foal syndrome, results in the inability to produce the proteins needed to keep the skin on the body. Affected foals exhibit symptoms within days of birth, including blisters at the pressure points, detachment of the hooves, and oral ulcers. As there is no treatment, affected foals are humanely euthanized. JEB2 is an autosomal recessive condition, thus a horse must inherit two copies of the allele (jeb2/jeb2) to show any signs. Horses with only one copy of the variant (jeb2/n) are known as carriers due to their ability to produce affected foals.

Gene Information

LAMA3 is a subunit of a key component of basement membranes. Mutations in other subunits of this complex have been shown to result in JEB2 in many human populations. This particular mutation is a 6,589 bp deletion spanning exons 24-27 that disrupts the normal amino acid sequence, resulting in a truncated protein.

Carrier frequency: estimated at slightly more than 5% in American Saddlebreds

References

K. T. Graves, P. J. Henney and R. B. Ennis. Partial deletion of the LAMA3 gene is responsible for hereditary junctional epidermolysis bullosa in the American Saddlebred Horse. (2008) Animal Genetics, 40, 35–41