The precise classification of epidermolysis bullosa (EB) into 4 main types and more than 30 subtypes is based on the level of skin cleavage, as well as clinical and molecular features, and is crucial for early prognostication, case management, genetic counselling and prenatal or pre-implantation diagnosis. We report here the molecular pathology of 40 consecutive cases of suspected EB, which were investigated by immunofluorescence mapping (IFM) and/or by a targeted next-generation sequencing (NGS) multi-gene panel. IFM correctly established the EB subtype in 76% of cases, while the molecular pathology was completely elucidated in 90% of cases by the targeted NGS multi-gene panel. Thirteen previously unreported mutations in EB genes were identified. In cases with unclear clinical and IFM findings, mutations were found by NGS in previously unexpected genes. IFM was useful in delivering fast results in newborns, and in indicating the consequences of the variants of uncertain significance on protein level. This study underscores the efficacy of the strategy of combining targeted NGS with IFM in resolving unusual EB phenotypes. It also suggests that, despite technological advances, careful clinical evaluation and deep phenotyping remains a crucial factor that dictates successful diagnosis of EB.

We estimate the frequency of PNPLA1 mutations among patients with ARCI to be around 3%. Most of our patients were born as collodion babies and showed a relatively mild ichthyosis phenotype. In four unrelated patients we observed a cyclic scaling course, which seems to be a potential phenotypic variation in a small percentage of patients with PNPLA1 mutations. The variability of the clinical manifestations and the lack of typical clinical features are specific for patients with PNPLA1 mutations, and emphasize the importance of DNA sequencing for differential diagnosis of ARCIs.

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of rare disorders of keratinization characterized by generalized abnormal scaling of the skin. Ten genes are currently known to be associated with ARCI: TGM1, ALOXE3, ALOX12B, NIPAL4 (ICHTHYIN), ABCA12, CYP4F22, PNPLA1, CERS3, SDR9C7, and SULT2B1. Over a period of 22 years, we have studied a large patient cohort from 770 families with a clinical diagnosis of ARCI. Since the first report that mutations in the gene CYP4F22 are causative for ARCI in 2006, we have identified 54 families with pathogenic mutations in CYP4F22 including 23 previously unreported mutations. In this report, we provide an up-to-date overview of all published and novel CYP4F22 mutations and point out possible mutation hot spots. We discuss the molecular and clinical findings, the genotype-phenotype correlations and consequences on genetic testing.