893 Development of a testing and diagnostics platform dedicated to rare genetic variants of uncertain significance (VUS) identified in patients with congenital ichthyosis

Congenital ichthyoses are rare genodermatoses caused by mutations in genes (more than 60 identified so far) involved the epidermal barrier. Five to 10% of genetic variants not described and their pathogenicity demonstrated, hence resulting “variants uncertain significance” (VUS) before causality is established. This leaves patients formally undiagnosed, precluding prognosis, counselling treatment. Most VUS missense for which it needed develop a standardized process evaluate pathogenicity. The task complex due vast number ichthyosis-causing genes. To address question, we developed CRISPR-Cas9-knockout production immortalized keratinocytes (N/TERT-2G). Each tested corresponding KO cell-line transduction with lentiviral vector encoding wild type or protein. cells then used produce reconstructed human epidermis that can be phenotypically analysed set assays depending on nature function concerned gene: protein expression stability (western blot, immunofluorescence), stratum corneum lipid profile (LC-MS/MS), barrier functionality (transepidermal water loss, dye permeability). We primarily targeted autosomal recessive congenital strategy was successfully characterize 3 PNPLA1. opens possibility extend approach qualify ‘on demand’ other Ultimately, such development will broaden spectrum harboring causal ichthyoses, thereby reducing diagnosis deadlocks improving management patients.