ELOVL4 and autosomal recessive congenital ichthyosis: Until now, several important steps for acyceramide biosynthesis and processing in the epidermis have been identified from studies of autosomal recessive congenital ichthyosis (ARCI) in humans and corresponding mouse disease models with genetic knockouts: the synthesis of ULCFAs by the FA elongase ELOVL4, ω-hydroxylation of ULCFAs by the FA ω-hydroxylase CYP4F22 (or CYP4F39 in mice), and formation of ceramides with ULCFAs by the ceramide synthase CERS3 (refs 18, 19, 20).