Molecular mechanisms of phenotypic variability in junctional epidermolysis bullosa

Background: Junctional epidermolysis bullosa (JEB), a group of hereditary skin fragility disorders, is associated with a wide variety of phenotypes, although all forms are characterised by trauma induced skin blistering and tissue separation at the dermaleepidermal junction zone. A subgroup, coined JEB-other, is associated with mutations in the COL17A1 gene encoding collagen XVII or, more rarely, with mutations in the laminin 332 genes LAMA3, LAMB3, or LAMC2. The objective of this study is comprehensive genotypeephenotype analysis in JEB-other patients with COL17A1 mutations and elucidation of disease mechanisms underlying different skin phenotypes. Methods and results: COL17A1 mutations and their clinical and cellular consequences were systematically analysed in 43 patients with JEB-other. Cell culture, RT-PCR, and protein biochemistry were applied to assess the effects of splice site mutationsdthat is, the nature and amounts of transcripts and polypeptides synthesised and their association with the phenotypic outcome. 34 distinct COL17A1 mutations were disclosed, 12 of them novel. mRNA and protein analyses demonstrated that patients with only about 12-14% of the physiological collagen XVII levels had mild cutaneous involvement and a long life span. Conclusions: In contrast to complete null phenotypes, presence of minor amounts of collagen XVII protein in JEB skin is associated with mild phenotypic manifestations. The data have significant implications for design of molecular therapies for JEB, since they suggest that already a low extent of collagen XVII restoration will improve skin stability and alleviate symptoms.