Human type VII collagen: genetic linkage of the gene (COL7A1) on chromosome 3 to dominant dystrophic epidermolysis bullosa

Abstract

Epidermolysis bullosa (EB) is a heterogeneous group of heritable blistering disorders affecting the skin and the mucous membranes. Previous ultrastructural studies on the dystrophic (scarring) forms of EB have demonstrated abnormalities in the anchoring fibrils, morphologically distinct structures below the basal lamina at the dermal/epidermal basement membrane zone. Type VII collagen is the major collagenous component of the anchoring fibrils, and it is therefore a candidate gene for mutations in some families with dystrophic forms of EB. In this study, we performed genetic linkage analyses in a large kindred with dominant dystrophic EB. A 1.9-kb type VII collagen cDNA clone was used to identify a PvuII RFLP to follow the inheritance of the gene. This RFLP cosegregated with the EB phenotype in this family, strongly supporting genetic linkage (Z = 5.37; theta = .0). In addition, we assigned the type VII collagen gene (COL7A1) to chromosome 3 by hybridization to a panel of human x rodent somatic cell hybrids. These data demonstrate very close genetic linkage between the clinical phenotype in this family and the polymorphism in the type VII collagen gene mapped to chromosome 3. The absence of recombination between EB and the type VII collagen gene locus, as well as the observed abnormalities in the anchoring fibrils, strongly suggest that this collagen gene is the mutant locus in this kindred.