Epidermolysis bullosa with pyloric atresia: novel mutations in the beta4 integrin gene (ITGB4).
Epidermolysis bullosa with pyloric atresia (EB-PA; OMIM 226730) is a clinically and genetically heterogeneous autosomal recessive blistering disorder, including lethal and nonlethal variants. Recently, expression of alpha6beta4 integrin, a transmembrane protein of the epithelial basement membranes, has been shown to be altered in these patients. In this work, we have explored the molecular pathology of the lethal form of EB-PA, and we describe novel ITGB4 mutations in five alleles of three patients. The mutation detection strategy included polymerase chain reaction amplification of each exon of ITGB4, followed by heteroduplex analysis and direct nucleotide sequencing. The novel mutations included a homozygous 2-bp deletion in exon 34 (4501delTC), compound heterozygosity for a 2-bp deletion within the paternal allele (120delTG) within exon 3 and a cysteine substitution in the maternal allele (C245G) within exon 7, and the paternal nonsense mutation within exon 4 (Q73X). Thus, three of four distinct mutations predicted truncated polypeptide chains, whereas the missense mutation in the extracellular domain of beta4 integrin may affect ligand binding or dimerization of alpha6 and beta4 integrin subunits. These mutations emphasize the critical importance of the alpha6beta4 integrin in providing stability to the association of epidermis to the underlying dermis at the cutaneous basement membrane zone.