LAMB3 mutations in generalized atrophic benign epidermolysis bullosa: consequences at the mRNA and protein levels

Generalized atrophic benign epidermolysis bullosa (GABEB; OMIM no. 226650) is a rare hemidesmosomal variant of EB, inherited in an autosomal recessive fashion. In previous studies, mutations in the gene (COL17A1) encoding the type XVII collagen, a transmembrane component of hemidesmosomes, were detected in most patients with GABEB. However, evidence for genetic defects in the laminin 5 genes has also been presented. In the present investigation, we examined three patients, representing two families with GABEB, for mutations in the LAMB3 gene. Heteroduplex scanning of the gene, followed by direct automated sequencing, revealed that Patient 1 was a compound heterozygote for a missense mutation (C293S) and a premature termination codon-causing mutation (1367delAC). The latter mutation resulted in accelerated mRNA decay, which rendered the corresponding mRNA transcript undetectable by reverse transcriptase-PCR. Patients 2 and 3, siblings with slightly different clinical presentations, were homozygous for a G-->A transition affecting the last nucleotide of exon 7 (628G-->A). This mutation resulted in amino acid substitution (E210K), as well as in multiple aberrant splice variants affecting exons 6 to 8. These observations expand the repertoire of LAMB3 mutations in nonlethal variants of EB, and they illustrate the consequences of the mutations at the mRNA and protein levels.