CYP17A1 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: Although pathogenic variants have been identified in several genes, including CYP11B1, CYP17A1, HSD3B2, POR, STAR, and CYP11A1, approximately 95% of CAH cases are caused by 21-hydroxylase deficiency (21-OHD), primarily due to mutations in the CYP21A2 gene [1,2].