Steryl sulfatase (formerly arylsulfatase C, ARSC) hydrolyses sulfate from steroid sulfates (Noel et al. 1983, Vaccaro et al. 1987, Suzuki et al. 1992). It is located on the ER membrane (Stein et al. 1989) and functions as a homodimer, using calcium as a cofactor. Defects in STS are the cause of ichthyosis X-linked (IXL) (MIM:308100), a keratinisation disorder (Basler et al. 1992, Alperin & Shapiro 1997).