Junctional epidermolysis bullosa (veterinary medicine)

Junctional epidermolysis bullosa (JEB) is an inherited disorder that is also known as red foot disease or hairless foal syndrome. JEB is the result of a genetic mutation that inhibits protein production that is essential for skin adhesion. Therefore, tissues, such as skin and mouth epithelia, are affected. As a result, blisters form over the entire body causing pain and discomfort. Also, the open sores leave the newborn foal highly susceptible to secondary infection. The condition can be categorized into two types of mutations: JEB1 and JEB2. JEB1 is found in Belgian Draft horses, as well as other related Draft breeds. In contrast, JEB2 is found in American Saddlebred horses.

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.

JEB also affects the human population. Symptoms are closely related to those that are seen in horses. Blisters occur over a large portion of the body and are very susceptible to agitation. There are other symptoms associated, such as alopecia (hair loss), abnormalities of fingernails and toenails, and joint deformities. Children born with JEB may not live past the first year of age if the condition is severe enough. Other children that have a less severe case of JEB may live a normal lifespan.

JEB is an autosomal recessive trait; 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

Foals which are homozygous recessive (J/J) do not make it to reproductive age, so cannot be a parent. Carriers (N/J) do not display symptoms and have normal skin.

Mutations in the 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.

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