CYP21A2 and congenital adrenal hyperplasia: Steroid 21-hydroxylase deficiency (21-OHD) caused by mutations in the CYP21A2 gene located on the short arm of chromosome 6 [3] accounts for more than 90% of CAH cases [4].CAH resulting from 21-hydroxylase deficiency can be classified into two clinical forms according to the complete deficiency and partial deficiency of enzyme activity: classical (either salt-wasting or simple virilization) and non-classical [5].