<prompt> Which is the most common variant of congenital adrenal hyperplasia?11b hydroxylase deficiency17a hydroxylase deficiency3b hydroxyl-steroid dehydrogenase21 hydroxylase deficiency  <response>: Mutations in CYP21A2 which leaads to 21 hydroxylase deficiency is the most prevalent cause of CAH responsible for 90-95 of cases. 