Junctional epidermolysis bullosa (JEB) is a heterogeneous autosomal recessively inherited blistering skin disorder associated with fragility at the dermal-epidermal junction. Characteristic ultrastructural findings in JEB are abnormalities in the hemidesmosome-anchoring filament complexes. These focal attachment structures, which extend from the intracellular compartment of the basal keratinocytes to the underlying basement membrane, have been shown to be hypoplastic or rudimentary in different forms of JEB. Previously, in different JEB phenotypes, mutations have been found in the three genes for the anchoring filament component laminin 5 (LAMA3, LAMB3, and LAMC2) and in the gene for the hemidesmosome-associated integrin beta 4 subunit. Here, we describe the first mutations in the gene encoding the 180-kD bullous pemphigoid antigen (BPAG2), a transmembranous hemidesmosomal collagen, also known as type XVII collagen (COL17A1). The patient is affected with generalized atrophic benign epidermolysis bullosa (GABEB), a rare variant of JEB, and is a compound heterozygote for premature termination codons on both alleles. These novel findings emphasize the molecular heterogeneity of this group of genodermatoses, and attest to the importance of BPAG2 in maintaining adhesion between the epidermis and the dermis.

We have analysed the expression of keratins in the epidermis of normal human palm and sole skin (ridged skin) using immunohistochemistry and in situ hybridization. The epidermis of human ridged skin expresses a more complex pattern of keratins than thin skin, which is probably due to the greater stress that ridged skin has to withstand. In addition to keratin K9, we document specific expression patterns of keratins K6, K16 and K17 which are suggestive of regional adaptations of this epidermis to a high cell turnover rate. In particular, the sequestered location of nests of K17-positive cells at the bottom of the deep primary epidermal ridges supports the notion of functional heterogeneity of basal cells and suggests that the K17-positive sites may include stem cells. Expression of K6 and K16 in some basal and most suprabasal keratinocytes is compatible with a constitutively high proliferative activity of normal ridged epidermis, but may also reflect different physical properties of the suprabasal cells, in contrast with regions expressing K9. The distinct labelling patterns observed in primary and secondary epidermal ridges as well as epidermal layers above dermal papillae suggest the existence of local microenvironmental niches leading to differences in keratinocyte differentiation.

The inherited mechanobullous disorder, junctional epidermolysis bullosa (JEB), is characterized by extensive blistering and erosions of the skin and mucous membranes. The diagnostic hallmarks of JEB include ultrastructural abnormalities in the hemidesmosomes of the cutaneous basement membrane zone, as well as an absence of staining with antibodies against the anchoring filament protein, laminin 5. Therefore, the three genes encoding alpha 3, beta 3 and gamma 2 chains of laminin 5, known as LAMA3, LAMB3 and LAMC2, are candidate genes for JEB. We have previously demonstrated mutations in the LAMB3 and LAMC2 genes in several families with JEB. We initiated mutation analysis from an affected child by PCR amplification of individual LAMA3 exons, followed by heteroduplex analysis. Nucleotide sequencing of heteroduplexes identified a homozygous nonsense mutation within domain I/II of the alpha 3 chain. These findings provide the first evidence that nonsense mutations within the LAMA3 gene are also involved in the pathogenesis of JEB, and indicate that mutations of all three genes of laminin 5 can result in the JEB phenotype.

We report the case of a 72-year-old man with clinical features resembling those of non-lethal junctional epidermolysis bullosa associated with IgG autoantibodies to the beta chain of laminin-5. The patient presented with a sudden onset of blistering and severe fragility of the skin and mucous membranes resulting in atrophic scars. Electron microscopy showed that the blistering arose in the lamina lucida. Indirect immunofluorescence indicated that the autoantibodies bound to the dermal side of 1 mol/L NaCl-split skin, and both direct and indirect immunoelectron microscopy demonstrated antibody binding to the lamina densa. Postembedding immunogold electron microscopy also revealed labelling in the lamina lucida beneath the hemidesmosomes. On immunoblotting, we found the autoantibodies to comigrate with the beta chain of laminin-5. Following the nomenclature of inherited junctional epidermolysis bullosa with mutations of the laminin-5 gene, we propose the name acquired junctional epidermolysis bullosa for this newly recognized disease.

Junctional epidermolysis bullosa associated with pyloric atresia (EB-PA; OMIM 226730) is a rare autosomal recessively inherited disease in which mucocutaneous fragility is associated with gastrointestinal atresia. This disease is usually fatal within the first few weeks or months of life even following surgical correction of the intestinal obstruction. Recently, mutations in the genes encoding the epithelial integrin alpha6beta4 (ITGA6 and ITGB4) have been identified in several patients with EB-PA. We report two unrelated patients with this disease who have survived into early childhood with mild cutaneous involvement, in whom we have identified pathogenetic mutations in ITGB4. The first patient was a compound heterozygote for a splice site mutation in exon 30 (3793 + 1G-to-A) and a non-sense mutation in exon 36 (W1478X), and the second was a compound heterozygote for a missense mutation in exon 3 (C38R) and a 1 bp deletion in exon 36 (4776delG). Although the non-sense and deletion mutations are predicted to result in markedly reduced beta4 integrin mRNA levels, the presence of the missense or splice site mutation on the second allele may enable the synthesis of some functional, albeit perturbed, beta4 polypeptide. Determination of the molecular mechanisms in these two cases increases our understanding of EB-PA and may enable correlation between genotype and phenotype.