CYP21A2 and congenital adrenal hyperplasia: According to the types of known defective enzymes (genes), CAH can be divided into 7 types [9–14], including 21-OHD (encoded by CYP21A2 gene), 11β-OHD (encoded by CYP11B1 gene), 17-OHD (encoded by CYP17A1 gene), 3β-HSD deficiency (encoded by HSD3B2 gene), LCAH (encoded by StAR Gene), PORD (encoded by POR gene) and cholesterol side-chain cleavage enzyme deficiency (P450cc deficiency, encoded by CYP11A1 gene).