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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, called J, explains this disease in Belgians and related draft breeds; and another, called J2, is found in Saddlebreds and related breeds. It is likely that additional yet-unidentified variants may exist that explain the JEB phenotype in other breeds.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, J =Junctional epidermolysis bullosa, Belgian variant
Breeds appropriate for testing: Belgian, Breton, Comtois
Explanation of Results:
- Horses with N/N genotype will not have junctional epidermolysis bullosa and will not transmit this JEB variant to their offspring.
- Horses with N/J 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 J/J genotype will have junctional epidermolysis bullosa, a fatal condition.
$45 one test per animal
*Members of the Belgian Draft Horse Corporation of America are advised to order testing directly through the registry.*
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 mutations 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, mutations in LAMA3 and LAMC2 have been shown to result in JEB.
In Belgian Draft horses and derivatives of that breed, a recessive mutation J in the LAMC2 gene (AY082802.1:c.1571_1572insC) was identified as the cause of junctional epidermolysis bullosa. The insertion in LAMC2 results in a premature termination codon and thus a non-functional laminin-5.
Two copies J 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 detects the known causal variants for JEB. 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/J) to non-carriers (N/N) without the worry of producing an affected foal.
Species
Breed
| Test Result | Junctional Epidermolysis Bullosa |
|---|---|
| N/N | Normal. Horse does not have the variant associated with junctional epidermolysis bullosa 1 identified in the Belgian |
| N/J | Carrier. Horse has one copy of the variant associated with junctional epidermolysis bullosa 1 identified in the Belgian. |
| J/J | Affected. Horse has two copies of the variant associated with junctional epidermolysis bullosa 1 identified in the Belgian. 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
Milenkovic, D., Chaffaux, S., Taourit, S., & Guérin, G. (2003). A mutation in the LAMC2 gene causes the Herlitz junctional epidermolysis bullosa (H-JEB) in two French draft horse breeds. Genetics Selection Evolution, 35(2), 249. doi: 10.1186/1297-9686-35-2-249
Cappelli, K., Brachelente, C., Passamonti, F., Flati, A., Silvestrelli, M., & Capomaccio, S. (2015). First report of junctional epidermolysis bullosa (JEB) in the Italian draft horse. BMC Veterinary Research, 11(1). doi: 10.1186/s12917-015-0374-0
