Epidermolysis bullosa is the name given to a group of genetically determined disorders, which are characterised by an excessive susceptibility of the skin and mucosae to separate from the underlying tissues following mechanical trauma. The individual diseases vary in their impact from relatively minor disability (e.g. limitation of walking distance because of blistering of the feet), to death in infancy. There are three broad categories of epidermolysis bullosa: epidermolysis bullosa simplex, dystrophic epidermolysis bullosa and junctional epidermolysis bullosa. Within each of these categories, there are several sub-types which are clinically, and probably genetically, distinct.
Types and Causes
EB Simplex - A group of inherited disorders characterised by mechanically induced blistering occurring within the epidermis itself, as a result of lysis of the basal keratinocytes (breakdown of epidermal skin cells). There are several established variants, of which the following are the most important:
Weber-Cockayne type -epidermolysis bullosa localised to the hands and feet.
Koebner type - generalised epidermolysis bullosa simplex.
Dowling-Meara type - epidermolysis bullosa simplex herpetiformis.
EB Simplex with muscular dystrophy.
In addition, there are a number of rarer variants which are encountered from time to time. The prevalence of the different forms of epidermolysis bullosa simplex can only be estimated. Weber-Cockayne type is probably 10-20 cases per million population, Koebner is rarer, possibly about 2 cases per million and Dowling-Meara appears to be in the region of 5-10 cases per million. Almost all forms of epidermolysis bullosa simplex are inherited as autosomal dominant traits, although some rare forms are inherited as autosomal recessive traits. People with the generalised and the localised forms almost always have extensive family histories of the condition.
Dystrophic epidermolysis bullosa - A group of inherited disorders characterised by mechanically induced blistering occurring immediately below the lamina densa of the basement membrane zone. These disorders derive the name dystrophic from the tendency of the blisters to heal with atrophic scarring. Dystrophic epidermolysis bullosa may be inherited as an autosomal dominant or an autosomal recessive trait. In general, it tends to be most severe when inherited as a recessive, and mildest when inherited as a dominant, but there is considerable clinical overlap. There are few data to indicate the prevalence of dystrophic epidermolysis bullosa. A recent study in Scotland indicated an estimated prevalence of 21.4 cases per million.
Junctional epidermolysis bullosa - A group of inherited disorders characterised by mechanically induced blistering occurring within the basement membrane at the level of the lamina lucida. There are three broad types of junctional epidermolysis bullosa:
Herlitz junctional epidermolysis bullosa - in which death is probable within the first two years of life.
Non-Herlitz junctional epidermolysis bullosa - in which many people will survive into adult life.
Junctional epidermolysis bullosa -with pyloric atresia.
Because most affected individuals die early in life, the incidence of junctional epidermolysis bullosa is particularly difficult to ascertain. It is estimated that the incidence of new cases is approximately the same as for dystrophic epidermolysis bullosa, i.e. around 20 per million births. To date, all types of junctional epidermolysis bullosa have been transmitted as autosomal recessive traits.
Symptoms and Treatments
Due to the large number of different forms of epidermolysis bullosa with greatly differing symptoms and prognoses, it is unwise to try to describe these in any detail here. Broadly, the common features of the condition relate to blistering of the skin and mucosae at the slightest friction. In some forms the blistering is confined to particular areas of the body, such as the hands and feet. In others the blistering can affect all of the body. The blistered areas in some forms of epidermolysis bullosa heal normally, in others healing is accompanied by scarring.
In view of this, specific information should always be obtained from a competent clinician who will be able to relate the information given to the precise form of epidermolysis bullosa that the person has. The patient support group DEBRA can provide the names of clinicians and other health care professionals who have a specialist interest in, and knowledge of, the condition.
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