Junctional Epidermolysis Bullosa (JEB)

Junctional epidermolysis bullosa is a severe inherited disease characterized by extreme fragility of the skin and mucous membranes. Affected foals may show signs at birth or shortly thereafter, including blister formation, extensive abrasions, and open wounds following even minimal mechanical irritation. The lips, oral mucosa, lower parts of the limbs, and the coronary band of the hoof are typically affected. Damaged areas may subsequently develop secondary infections. Lesions in the oral cavity may prevent normal suckling, and affected foals may die shortly after birth. The disease has been described mainly in certain draft horse breeds, including the Belgian Draft Horse, Breton Horse, and Comtois.

JEB is caused by the c.1372dup mutation in the LAMC2 gene, which encodes the laminin gamma-2 chain. Laminin is an important component of structures that ensure the firm attachment of surface epithelial cells to the underlying tissue in both skin and mucous membranes. The mutation disrupts this connection, causing tissue layers to separate easily under minimal mechanical stress, resulting in blisters, erosions, and open wounds.

The mutation is inherited in an autosomal recessive manner. This means that the disease develops only in individuals that inherit the mutated gene from both parents. Carriers of the mutation are clinically healthy but transmit the mutation to their offspring. Mating of two heterozygous carriers theoretically results in 25% healthy offspring, 50% carrier offspring, and 25% affected offspring inheriting the mutation from both parents.

Genetic testing enables reliable identification of mutation carriers and helps prevent the birth of affected foals through appropriate breeding management.

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Reference:

Spirito, F., Charlesworth, A., Linder, K., Ortonne, JP., Baird, J., Meneguzzi, G.: Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse. J Invest Dermatol 119:684–691, 2002. PubMed reference: 12230513