Genotype and phenotype correlations in 441 patients with epidermolysis bullosa from China

BACKGROUND: Epidermolysis bullosa (EB) is a heterogeneous group of rare and incurable genetic blistering disorders. OBJECTIVES: The objective was to analyse the genotype-phenotype correlation in EB among Chinese individuals. METHODS: Next-generation sequencing and Sanger sequencing were performed to genetically confirm clinically diagnosed EB. Reverse transcription-PCR and splice-site analysis were used to evaluate the consequences of splicing mutations. RESULTS: A total of 441 cases (413 families) across 11 genes were included. EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), Kindler EB, simplex and junctional compound EB accounted for 23.4%, 12.7%, 61.5%, 1.1% and 0.2%, respectively. In 16 probands with presumptive recessive EB, failed to find the second allele, COL7A1 (10), COL17A1 (4), LAMB3 (1) and ITGB4 (1). De novo mutations are common in dominant EB (63.8% in EBS, 27.5% in DEB) but extremely rare in recessive DEB (RDEB; 0.74%). Mosaicism is more common than presumed, with 5.4% of dominant EBS. In JEB, only 45.0% of patients with biallelic premature termination codon (PTC) mutations in laminin 332 genes died within 24 months, with a longer average survival age of 11.1 months. In JEB, unusual phenotypes are frequently observed, notably urinary tract involvement, duodenal atresia and EB nevi. In RDEB, 48.8% of cases with biallelic PTC mutations in COL7A1 exhibited a relatively mild phenotype; they are likely to develop a severe phenotype at 0-4 years old, and the PTC mutations position closer to the N-terminal, leading to earlier onset. Glycine substitution mutations in DEB have complex genotypic and phenotypic heterogeneity. The rare subtype, dominant and recessive compound DEB, consists of 1.8% of the total DEB. CONCLUSIONS: This study reveals the general rules governing genotype-phenotype correlations, rare phenotypes and complex genotypes. Collectively, mutation analysis in different forms of EB provides the basis for improved subclassification with accurate genetic counselling and for prenatal diagnosis.