Large decreases in or loss of acylceramide due to mutations in the genes involved in acylceramide synthesis (such as CERS3, CYP4F22 and ELOVL4) causes non-syndromic ARCI (CERS3 and CYP4F22) as described above, or a syndromic form of ichthyosis (ELOVL4) (refs 5, 8, 10, 12, 21). This evidence concerns the gene ELOVL4 and ichthyosis.