Junctional EB (JEB), also called lamina lucidoytic EB, is caused by a mutation in one of these genes: laminin-332 (also known as laminin-5), collagen XVII or α6β4 integrin. These genes contribute to forming the structural components of the skin known as hemidesmosones and anchoring filaments, which keep the outer layer of the skin, the epidermis, attached to the deeper layer of the skin, the dermis. When these components are abnormally formed, the layers of the skin will separate, and a blister will form.
Junctional EB is the least common subtype of EB. According to the National EB Registry data, approximately 10 percent of people with epidermolysis bullosa have junctional EB. All subtypes of junctional EB are inherited as a recessive disorder. Both parents of an affected child carry an abnormality or mutation in the affected gene. With recessive traits and disorders, two copies of the gene are required in order for the trait or disorder to be present; therefore the parents do not have EB. They are called “carriers.” In order for EB to occur in their children, both parents must pass the abnormal copy of the gene to the child. There is a 25 percent chance (1:4) with each pregnancy that the child will have the disorder; likewise, there is a 75% chance that the child will not, although the child still may be a carrier for the gene mutation.