A term neonate develops ambiguous genitalia (virilized female, 46,XX karyotype), hyponatremia (Na+ 120 mEq/L) and hyperkalemia (K+ 7.2 mEq/L) with hypotension on day 7 of life. 17-hydroxyprogesterone is grossly elevated. The enzyme deficient in the most common form of this disorder is:
- A 11-beta hydroxylase
- B 21-hydroxylase ✓
- C 17-alpha hydroxylase
- D 3-beta hydroxysteroid dehydrogenase
Explanation
Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency accounts for 90–95% of all CAH cases. This enzyme is required for conversion of 17-OHP to 11-deoxycortisol and progesterone to deoxycorticosterone; its deficiency causes cortisol and aldosterone deficiency with accumulation of 17-OHP and androgens. The salt-wasting form (aldosterone deficiency) presents in the first 1–2 weeks with hyponatremia, hyperkalemia, hypoglycemia and shock. 11-beta hydroxylase deficiency causes virilization with hypertension (not salt wasting). 17-alpha hydroxylase deficiency causes sexual ambiguity in males and primary amenorrhea with hypertension.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.