What are the genetic changes related to junctional epidermolysis bullosa ?
Junctional epidermolysis bullosa results from mutations in the LAMA3, LAMB3, LAMC2, and COL17A1 genes. Mutations in each of these genes can cause Herlitz JEB or non-Herlitz JEB. LAMB3 gene mutations are the most common, causing about 70 percent of all cases of junctional epidermolysis bullosa.  The LAMA3, LAMB3, and LAMC2 genes each provide instructions for making one part (subunit) of a protein called laminin 332. This protein plays an important role in strengthening and stabilizing the skin by helping to attach the top layer of skin (the epidermis) to underlying layers. Mutations in any of the three laminin 332 genes lead to the production of a defective or nonfunctional version of this protein. Without functional laminin 332, cells in the epidermis are fragile and easily damaged. Friction or other minor trauma can cause the skin layers to separate, leading to the formation of blisters.  The COL17A1 gene provides instructions for making a protein that is used to assemble type XVII collagen. Collagens are molecules that give structure and strength to connective tissues, such as skin, tendons, and ligaments, throughout the body. Type XVII collagen helps attach the epidermis to underlying layers of skin, making the skin strong and flexible. Mutations in the COL17A1 gene prevent the normal formation of collagen XVII. As a result, the skin is less resistant to friction and minor trauma and blisters easily. Most COL17A1 gene mutations cause non-Herlitz JEB, although a few individuals with mutations in this gene have had the more severe Herlitz JEB.