A term newborn assigned female at birth has clitoromegaly and fused labioscrotal folds. On day 9 she develops vomiting, poor feeding, dehydration, sodium of 126 mEq/L, potassium of 6.8 mEq/L, and hypotension. Serum 17-hydroxyprogesterone is markedly elevated. Which enzymatic defect explains this presentation?

• A 11-beta-hydroxylase deficiency
• B 17-alpha-hydroxylase deficiency
• C 5-alpha-reductase type 2 deficiency
• D 21-hydroxylase deficiency ✓

Explanation

21-hydroxylase deficiency is the commonest form of congenital adrenal hyperplasia. Blocked conversion of 17-hydroxyprogesterone diverts precursors into the androgen pathway, causing prenatal virilization, while combined cortisol and aldosterone deficiency produces the salt-wasting crisis with hyponatremia and hyperkalemia seen here. Elevated 17-hydroxyprogesterone is the diagnostic marker. 11-beta-hydroxylase deficiency also virilizes but causes hypertension from deoxycorticosterone excess, and 17-alpha-hydroxylase deficiency causes hypertension without virilization.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.