CYP21A2 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD) caused by pathological variants in the CYP21A2 gene has been classified into a) the classical form that includes the severe salt-wasting (SW) and milder simple-virilizing (SV) forms and b) the non-classical (NC) form.