In most cases, epidermolysis bullosa is inherited. Researchers have identified more than 10 genes involved with skin formation that, if defective, may cause a type of epidermolysis bullosa. It's also possible to develop epidermolysis bullosa as a result of a random mutation in a gene that occurred during the formation of an egg or sperm cell.

Your skin comprises an outer layer (epidermis) and an underlying layer (dermis). The area where the layers meet is called the basement membrane zone. Where and when blisters develop depend on the type of epidermolysis bullosa.

The four main types of this condition are:

  • Epidermolysis bullosa simplex. This most common and generally mildest form usually begins at birth or during early infancy. In some people, mainly the palms of the hands and soles of the feet are affected. In epidermolysis bullosa simplex, the faulty genes are those involved in the production of keratin, a fibrous protein in the top layer of skin. The condition causes the skin to split in the epidermis, which produces blisters, usually without scar formation.

    If you have epidermolysis bullosa simplex, it's likely you inherited a single copy of the defective gene from one of your parents (autosomal dominant inheritance pattern). If one parent has the single faulty gene, there's a 50 percent chance that each of his or her offspring will have the defect.

  • Junctional epidermolysis bullosa. This usually severe type of the disorder generally becomes apparent at birth. In junctional epidermolysis bullosa, the faulty genes are involved in the formation of thread-like fibers (hemidesmosomes) that attach your epidermis to your basement membrane. This gene defect causes tissue separation and blistering in your basement membrane zone.

    Junctional epidermolysis bullosa is the result of both parents carrying one copy of the defective gene and passing on the defective gene (autosomal recessive inheritance pattern), although neither parent may clinically have the disorder (silent mutation). If both parents carry one faulty gene, there's a 25 percent chance each of their offspring will inherit two defective genes — one from each parent — and develop the disorder.

  • Dystrophic epidermolysis bullosa. This type, whose subtypes range from mild to severe, generally becomes apparent at birth or during early childhood. In dystrophic epidermolysis bullosa, the faulty genes are involved in the production of a type of collagen, a strong protein in the fibers that hold the deepest, toughest layer of your skin together. As a result, the fibers are either missing or nonfunctional. Dystrophic epidermolysis bullosa can be either dominant or recessive.

Epidermolysis bullosa acquisita (EBA) is another rare type of epidermolysis bullosa, which isn't inherited. Blistering associated with this condition occurs as the result of the immune system mistakenly attacking healthy tissue. It's similar to a condition called bullous pemphigoid, which also is related to an immune system disorder. EBA has been associated with Crohn's disease, an inflammatory bowel disease.

Sep. 27, 2011