CYP21A2 and congenital adrenal hyperplasia: Pathogenic variants in CYP21A2, often resulting from gene microconversions or large conversion/rearrangements with its pseudogene CYP21A1P, underlie most cases of 21-hydroxylase deficiency, and the residual enzyme activity of each variant largely determines whether patients present with salt-wasting, simple virilizing, or non-classic CAH.