CYP21A2 encodes steroid 21-hydroxylase, a cytochrome P450 enzyme essential for adrenal steroidogenesis 1. The enzyme catalyzes the hydroxylation at C-21 of progesterone and 17α-hydroxyprogesterone to form 11-deoxycorticosterone and 11-deoxycortisol, respectively, which are intermediate metabolites in the biosynthetic pathways of mineralocorticoids and glucocorticoids 1. CYP21A2 is located on chromosome 6 and functions as a monooxygenase that uses molecular oxygen and electrons from NADPH via cytochrome P450 reductase 2. Mutations in CYP21A2 cause congenital adrenal hyperplasia (CAH), accounting for over 95% of CAH cases 3. The disease presents as a spectrum ranging from severe salt-wasting forms to milder nonclassical forms, depending on the degree of enzyme deficiency 4. Classic CAH occurs in approximately 1 in 16,000 births and manifests with cortisol and aldosterone deficiencies, leading to virilization and potential salt-wasting crisis 4. Over 100 CYP21A2 mutations have been identified, with structure-function relationships determining clinical severity 5. The condition requires lifelong glucocorticoid replacement therapy and careful management during pregnancy and other stress conditions 6.