Junctional epidermolysis bullosa (JEB), or Epitheliogenesis Imperfecta (EI), is a genetic disorder found in horses. Although affected foals appear initially to be born healthy, clinical signs appear quickly, and they are usually euthanized not long after birth.
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JEB has documented in Belgian drafts, American Cream Draft, Breton drafts, Comtois, and American Saddlebreds. Of these horses, 12% of Belgians and 4% of Saddlebreds are thought to carry the disorder.
The mutation associated with the clinical signs of JEB in Belgian and French draft horses has been identified and is linked to the γ2 subunit of the laminin-5 gene. The mutation is a cytosine insertion in the genomic nucleic acid sequence of affected horses at position 1368 of the laminin γ2 encoding polynucleotide, a frame shift, and a premature termination codon. This results in an absent expression of the laminin γ2 polypeptide. An autosomal recessive mode of inheritance of this mutation has been verified.
JEB causes defect in the action of the protein needed to connect the dermis to the epidermis. This produces many symptoms, including:
There is no known treatment. Foals are usually euthanized after diagnosis, due to the pain associated with the disease. Those that are not euthanized usually die of infection within 2 weeks.
"Testing for Genetic Diseases." Equus 353. pp 42–43.