Recessive dystrophic epidermolysis bullosa caused by COL7A1 hemizygosity and a missense mutation with complex effects...

Loss-of-function mutations in the gene encoding type VII collagen, COL7A1, are the molecular basis of the blistering skin disorder, recessive dystrophic epidermolysis bullosa (RDEB). COL7A1 maps to a region of the short arm of chromosome 3 that has been found to be deleted in many types of malignancies. We have characterized the first case of a large genomic deletion in chromosome 3p21.31 that removes COL7A1 entirely in an RDEB patient. This interstitial deletion spans 255 to 520 kb and encompasses 9 to 15 genes, but seems to have no pathological consequences other than RDEB. We show that the second, hemizygous allele of COL7A1 in this patient bears a base substitution within exon 94, c.7245G>A. This translates into an amino acid substitution, p.M2415I, and leads to a complex splicing abnormality that allows marginal levels of functional mRNA and protein to be synthesized. We propose that the leakiness of the splicing defect enables the partial rescue of collagen VII deficiency. This is consistent with the diagnosis of the moderately severe form of RDEB in the proband, at variance with the most severe form, RDEB Hallopeau-Siemens, that would arise from complete collagen VII deficiency.