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| Epidermolysis Bullosa Acquisita |
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Definition: Epidermolysis bullosa comprises a group of heterogeneous diseases characterized by the development of subepidermal blisters after minor mechanical trauma to the skin. Description: The majority of the cases are inherited. Rare cases are acquired and are referred to as epidermolysis bullosa acquisita (EBA), which has an annual incidence of 0.2 cases per million in the western world. Diagnosis: The gold standard for the diagnosis of EBA is immuno-electron microscopy that shows the precise localization of the antibodies in the region below the lamina densa, where anchoring fibrils normally exist. Recently, an ELISA that uses recombinant NC1 as the coating antigen for the ELISA plates has proven to be a sensitive, specific and rapid tool for the screening of EBA sera. A recent review and update on EBA can be read in this reference (Ref 4). Types: There are at least five clinical phenotypes, all presenting in the fourth to fifth decade of life. Each phenotype shares qualitatively identical immunologic features (antibodies t o type VII collagen and diminished anchoring fibrils), but has unique histologic and ultrastructural changes. All phenotypes occur in both sexes and probably in all races. Pathogenesis: EBA is characterized by the presence of antibodies directed against type VII collagen, which is the major structural component of the anchoring fibrils, which attach the lamina densa of the basement membrane to the underlying dermis. Type VII collagen is composed of three identical alpha chains that wind into a triple helical structure. Each alpha chain is 290 kDa and is composed of three domains: at the N terminus there is a large, 145 kDa globular domain, called the non-collagenous 1 domain (NC1); in the center there is a long rod-shaped, helical, collagenous domain; and at the C terminus there is small (34 kDa) non-collagenous, globular domain, called NC2. Patients with EBA have antibodies mainly directed against NC1, which may comprise the function of type VII collagen, so that anchoring fibrils cannot interact well and bind to other connective tissue components of the basement membrane and papillary dermis. The loss of anchoring fibrils leads eventually to the formation of subepidermal blisters. There is, at the moment, only circumstantial evidence that EBA is an autoimmune disease. The clinical spectrum of EBA is still being defined. |
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Links to other Resources: www.debra.org www-med.stanford.edu www.med.unc.edu hometown.aol.com/carterga52/myhomepage/index.html |
