Epidermolysis bullosa. II. Type VII collagen mutations and phenotype-genotype correlations in the dystrophic subtypes

Background: The dystrophic forms of epidermolysis bullosa (DEB), a group of heritable blistering disorders, show considerable phenotypic variability, and both autosomal dominant and autosomal recessive inheritance can be recognised. DEB is derived from mutations in the type VII collagen gene (COL7A1), encoding a large collagenous protein that is the predominant, if not exclusive, component of the anchoring fibrils at the dermal epidermal junction. Methods: The Dystrophic Epidermolysis Bullosa Research Association Molecular Diagnostics Laboratory ( Philadelphia, Pennsylvania, USA), established in 1996, has analysed more than 1000 families with different forms of epidermolysis bullosa, among them 332 families with DEB. DNA specimens were subjected to mutation analysis by polymerase chain reaction (PCR) amplification of all 118 exons and flanking intronic sequences of COL7A1, followed either by heteroduplex scanning and sequencing of the PCR products demonstrating heteroduplexes or by direct nucleotide sequencing. Results: 355 mutant alleles out of the anticipated 438 (81.1%) were disclosed. Among these mutations, a total of 242 mutations were distinct and 138 were novel, previously unreported mutations. No evidence of mutations in any other gene was obtained. Discussion: Examination of the mutation database suggested phenotype - genotype correlations, contributing to the improved subclassification of DEB with prognostic implications. The mutation information also forms the basis for accurate genetic counselling and prenatal diagnosis in families at risk for recurrence.