A newborn has ambiguous genitalia with clitoromegaly and fused labioscrotal folds. At day 7 she becomes lethargic and feeds poorly. Sodium is 126 mEq/L, potassium 6.8 mEq/L, and glucose 52 mg/dL. Serum 17-hydroxyprogesterone is markedly elevated. Which enzyme deficiency explains this presentation?

• A 11-beta hydroxylase
• B 17-alpha hydroxylase
• C 5-alpha reductase
• D 21-alpha hydroxylase ✓

Explanation

Classic 21-hydroxylase deficiency accounts for about 90 to 95 percent of congenital adrenal hyperplasia. Blocked conversion of 17-hydroxyprogesterone to 11-deoxycortisol shunts precursors into androgen synthesis, causing virilisation, while aldosterone and cortisol loss produces the salt-wasting crisis with hyponatraemia and hyperkalaemia. 11-beta hydroxylase deficiency causes hypertension rather than salt wasting, and 17-alpha hydroxylase deficiency presents with hypertension and sexual infantilism, not virilisation.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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