STS and recessive X-linked ichthyosis: The XLI prevalence rate, based upon clinical diagnoses, is ~1 in 6000 males [1]; however, population-based endocrinological and genetic screening suggests that up to ~1 in 1500 males may be affected by steroid sulfatase deficiency (equivalent to ~2.5million males worldwide) indicating that lack of the STS enzyme is associated with a spectrum of phenotypic severity [3,4].