CYP21A2 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: More than 90% of CAH cases are due to 21-hydroxylase-deficiency (21-OHD) caused by mutations in CYP21A2. This deficiency has three subtypes: classic salt wasting (SW), classic simple virilising (SV), and non-classic (NC-21OHD) subtypes.