A newborn girl has ambiguous genitalia with clitoromegaly and fused labioscrotal folds. On day 9 she becomes lethargic and feeds poorly. Sodium is 126 mEq/L, potassium 6.8 mEq/L, and blood glucose 48 mg/dL. Pelvic ultrasound confirms a uterus and ovaries. Which enzyme defect explains these findings?

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

Explanation

Salt-wasting congenital adrenal hyperplasia from 21-hydroxylase deficiency causes aldosterone and cortisol lack, giving hyponatraemia, hyperkalaemia, and hypoglycaemia, together with androgen excess virilising a 46,XX infant. 11-beta hydroxylase deficiency causes hypertension from deoxycorticosterone excess, not salt wasting. 17-alpha hydroxylase deficiency underproduces androgens, and 5-alpha reductase deficiency affects only external genital development in 46,XY infants.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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