Effect of depletion of PNPLA1 in gene expression during keratinocyte differentiation on reconstructed human epidermis

Congenital ichthyoses are rare and disabling genodermatoses caused by mutations in genes involved in the epidermal barrier. More than 60 genes are known to be involved. However, 5-10% of the genetic variants identified in those genes are rarely or not described and their pathogenicity not yet demonstrated. They are therefore classified as Variants of Uncertain Significance (VUS) that leave number of patients undiagnosed, precluding prognosis, counselling and treatment. We report here, an experimental strategy to reclassify VUS identified in congenital ichthyosis-causing genes tested for PNPLA1 variants. PNPLA is a transacylase essential for the skin barrier formation. It catalyzes the biosynthesis of acylceramides (AcylCer) in the stratum granulosum by esterification of ω-hydroxy ceramides with linoleic acid. We successfully characterized three PNPLA1 VUS identified in three patients with congenital ichthyosis, opening the possibility to extend the approach to other ichthyosis-causing genes.