COMPOUND HETEROZYGOSITY FOR A NONSENSE MUTATION AND A SPLICE-SITE MUTATION IN THE TYPE-VII COLLAGEN GENE (COL7A1) IN RECESSIVE DYSTROPHIC EPIDERMOLYSIS-BULLOSA

Mutations in the type VII collagen gene (COL7A1) have recently been es tablished as the molecular basis of the inherited blistering skin diso rder, dystrophic epidermolysis bullosa. We report a novel combination of COL7A1 mutations in a Japanese patient with an autosomal recessive form of dystrophic epidermolysis bullosa. Clinically, the patient had suffered from generalized trauma-induced blistering since the first we ek of life, loss of most finger- and toenails, esophageal stenosis, an d partial fusion of the fingers acid toes. Immunofluorescence microsco py of the dermal-epidermal junction in the patient's skin revealed red uced intensity of staining with an anti-type VII collagen antibody. Tr ansmission electron microscopy showed only a few thin, poorly formed a nchoring fibrils. The patient was a compound heterozygote for a nonsen se mutation on one COL7A1 allele and a donor splice site mutation on t he other allele. The mutations were identified by PCR amplification of genomic DNA, heteroduplex analysis, and nucleotide sequencing, and ve rified by restriction endonuclease digestion. Reverse transcriptase-PC R and sequencing of cDNA from the patient's cultured keratinocyte mRNA showed evidence of aberrant splicing resulting from the donor splice site mutation, due to activation of a cryptic intronic splice site tha t leads to a frameshift and a downstream premature termination codon. Knowledge of the genetic lesions in this patient is helpful in elucida ting the molecular consequences of COL7A1 mutations in dystrophic epid ermolysis bullosa and in providing information about the fundamental m echanisms involved in maintaining adhesion between the epidermis and t he dermis.