STS and syndromic recessive X-linked ichthyosis: X-linked ichthyosis (XLI (OMIM: 308100)) is an uncommon dermatological condition characterised by the presence of large dark-brown scales,1 although much milder skin phenotypes have been reported2; it occurs due to deficiency of the enzyme steroid sulfatase (STS), encoded by the X-linked STS gene (OMIM: 300747).