Genetics
JEB is considered an autosomal recessive trait. This means that both parents must carry the recessive gene in order to have an affected offspring. If N represents a normal individual and J represents an affected individual, the following crosses indicate the rate of occurrence among related horses.
(N/J) x (N/J) = 50% N/J, 25% N/N, and 25% J/J
(N/N) x (N/J) = 50% N/N and 50% N/J
Homozygous recessive (J/J) is not considered because foals born with the disease do not make it to reproductive age. Carriers (N/J) do not display symptoms and have normal skin.
Mutations in certain genes, LAMB3, LAMC2, and COL17A1, are the cause of JEB. These genes are associated with the protein responsible for skin attachment to the underlying layers, laminin 332. When the genes undergo mutations, the protein is altered, making it dysfunctional. As a result, the skin is very fragile and may be damaged by even minor trauma.
Another protein, called type XVII collagen, is affected by a mutation in COL17A1. Due to this mutation, the defective protein is not able to produce collagen, which provides strength and structure for the skin. For this reason, the skins resistance to trauma is weakened.
Read more about this topic: Junctional Epidermolysis Bullosa (veterinary Medicine)