Most people with EB have inherited the condition through faulty genes they receive from one or both parents. Genes are located in the body’s cells and determine inherited traits passed from parent to child. They also govern every body function, such as the formation of proteins in the skin. More than 10 genes are known to underlie the different forms of EB. Genes are located on chromosomes, which are structures in each cell’s nucleus.
In an autosomal dominant form of EB, the disease gene is inherited from only one parent who has the disease, and there is a 50-percent (1 in 2) chance with each pregnancy that a baby will have EB. In the autosomal recessive form, the disease gene is inherited from both parents. Neither parent has to show signs of the disease; they simply need to “carry” the gene, and there is a 25-percent (1 in 4) chance with each pregnancy that a baby will have EB. EB can also be acquired through a mutation (abnormal change) in a gene that occurred during the formation of the egg or sperm reproductive cell in a parent. Neither the sex of the child nor the order of birth determines which child or how many children will develop EB in a family that has the faulty gene.
Although EB simplex can occur when there is no evidence of the disease in the parents, it is usually inherited as an autosomal dominant disease. In EB simplex, the faulty genes are those that provide instructions for producing keratin, a fibrous protein in the top layer of skin. As a result, the skin splits in the epidermis, producing a blister.
In junctional EB, there is a defect in the genes inherited from both parents (autosomal recessive) that normally promote the formation of anchoring filaments (thread-like fibers) or hemidesmosomes (hem-ee-DES-mo-soms) (complex structures composed of many proteins). These structures anchor the epidermis to the underlying basement membrane. The defect leads to tissue separation and blistering in the upper part of the basement membrane.
There are both dominant and recessive forms of dystrophic EB. In this condition, the filaments that anchor the epidermis to the underlying dermis are either absent or do not function. This is caused by defects in the gene for type VII collagen, a fibrous protein that is the main component of the anchoring filaments.
Epidermolysis bullosa acquisita (EBA) is a rare autoimmune disorder in which the body attacks its own anchoring fibrils with antibodies, the special proteins that help fight and destroy foreign substances that invade the body. In a few cases, it has occurred following drug therapy for another condition; in most cases, the cause is unknown.