CYP21A2 and congenital adrenal hyperplasia: Approximately 90–95% of CAH cases are caused by steroid 21-hydroxylase deficiency (21OHD, MIM 201910), resulting from mutations in the CYP21A2 gene and leading to a broad spectrum of clinical presentations, ranging from the severe classical salt-wasting (SW) and simple virilizing (SV) forms to the mild non-classical form of CAH [3, 4].