Ultrastructural Findings in Epidermolysis Bullosa

Abstract

Electron microscopy of skin provides diagnostic criteria for distinguishing the simplex, junctional, and dystrophic forms of inherited epidermolysis bullosa (EB). The plane of cleavage in blister formation indicates the localization of structural weakness within the epidermis and basement membrane zone, and, together with ultrastructural changes in affected skin, these are clues to the underlying genetic bases for these disorders. Skin biopsy specimens from individuals with EB were evaluated by electron microscopy to identify structural changes and determine the subtype of EB. Discrete, circumscribed clumps of keratin filaments present in the basal keratinocytes are pathognomonic for EB simplex Dowling-Meara. These and other observations of keratin filament disruption have led to the identification of mutations in keratin genes in Dowling-Meara and Koebner forms of EB simplex. Changes in the density and structure of anchoring fibrils and the relative amount of type VII collagen detected by immunostaining of the dermoepidermal junction in dystrophic EB have led to sequencing of mutations in the type VII collagen gene. Although mutations in junctional EB have not been reported, findings of structural alterations in hemidesmosomes and immunohistochemical studies of kalinin (BM600 and epiligrin), and in junctional EB with pyloric atresia alterations in the integrin alpha 6 beta 4, indicate molecules involved in basal keratinocyte adhesion to the basement membrane that are candidate genes for junctional EB. Electron microscopy of skin when correlated with mutations in EB will help us understand the significance of these structural molecules in normal skin and the pathogenesis of EB.