CYP21A2 and congenital adrenal hyperplasia: There are two forms of CAH: classic CAH, which is severe and life-threatening, attributable to the partial and complete ablation of residual enzyme activity and resulting in a lack of cortisol, and non-classic CAH, which is mild and caused by CYP21A2 mutations that retain almost 20–50% residual enzyme activity and sustained cortisol biosynthesis [1].