Definition and Causes of Epidermolysis Bullosa
article syndicated from NIAMS
updated about 1 year ago
This booklet is for people who have epidermolysis bullosa (ep-ee-der-MOL-eh-sis bull-O-sa, often called "EB"), parents and caregivers of children with EB, and others interested in learning more about the disease. The booklet describes the disease and its symptoms and contains information about diagnosis and treatment, as well as current research efforts supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and other components of the Department of Health and Human Services' National Institutes of Health (NIH). It also discusses issues such as skin care and quality of life for people with EB. If you have questions after reading this booklet, you may wish to discuss them with your doctor or a dermatologist (a specialist in treating skin conditions).
What Is Epidermolysis Bullosa?
EB is a group of blistering skin conditions. The skin is so fragile in people with EB that even minor rubbing may cause blistering. At times, the person with EB may not be aware of rubbing or injuring the skin even though blisters develop. In severe EB, blisters are not confined to the outer skin. They may develop inside the body, in such places as the linings of the mouth, esophagus, stomach, intestines, upper airway, bladder, and the genitals.
The skin has an outer layer called the epidermis and an underlying layer called the dermis. The place where the two layers meet is called the basement membrane zone. (See the diagram of the skin below.) The main forms of EB are EB Simplex, Junctional EB, and Dystrophic EB. EB Simplex occurs in the outer layer of skin; Junctional EB and Dystrophic EB occur in the basement membrane zone. These major types of EB, which will be described throughout this text, also have many subtypes.
Who Gets Epidermolysis Bullosa?
It is estimated that 2 to 4 out of every 100,000 people, or up to 12,000 people in the United States, have some form of EB. It occurs in all racial and ethnic groups and affects males and females equally. The disease is not always evident at birth. Milder cases of EB may become apparent when a child crawls, walks, or runs, or when a young adult engages in vigorous physical activity.
What Causes Epidermolysis Bullosa?
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 due to 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 where 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.
NIH Publication No. 03-7038 - Publication Date: June 2003
Acknowledgments:
The NIAMS gratefully acknowledges the assistance of Jo-David Fine, M.D., M.P.H., National EB Registry, Lexington, Kentucky; Martin I. Hassner, DebRA; Alan N. Moshell, M.D., NIAMS, NIH; Amy S. Paller, M.D., Children's Memorial Hospital, Chicago, Illinois; Jouni J. Uitto, M.D., Ph.D., Thomas Jefferson University, Philadelphia, Pennsylvania; and David T. Woodley, M.D., Los Angeles County/University of Southern California Medical Center, Los Angeles, California, in the preparation of this booklet.
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
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