A newborn girl develops vomiting, dehydration, and ambiguous genitalia with clitoromegaly. Labs show hyponatremia, hyperkalemia, markedly elevated 17-hydroxyprogesterone, and high renin. Which enzyme deficiency explains these findings, and what accumulates proximal to the block?
- A 11-beta hydroxylase deficiency; accumulation of 11-deoxycorticosterone causing hypertension
- B 21-hydroxylase deficiency; shunting of precursors into androgen synthesis with aldosterone and cortisol deficit ✓
- C 17-alpha hydroxylase deficiency; accumulation of mineralocorticoids causing hypertension
- D 3-beta hydroxysteroid dehydrogenase deficiency; accumulation of DHEA with salt wasting only
Correct answer: B. 21-hydroxylase deficiency; shunting of precursors into androgen synthesis with aldosterone and cortisol deficit
Explanation
21-hydroxylase deficiency accounts for about 90 percent of congenital adrenal hyperplasia. The block diverts steroid precursors into the androgen pathway, producing virilization, while impaired cortisol and aldosterone synthesis causes salt wasting with hyponatremia, hyperkalemia, and elevated 17-hydroxyprogesterone. Option A is the key distractor: 11-beta hydroxylase deficiency also virilizes but causes hypertension from deoxycorticosterone excess, not hypotension and hyperkalemia.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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