A 10-day-old female infant presents with vomiting, poor feeding, dehydration, sodium 124 mEq/L, potassium 6.9 mEq/L, and hypoglycaemia. Plasma 17-hydroxyprogesterone is markedly elevated. The enzyme deficiency responsible is:
- A 11-beta hydroxylase
- B 17-alpha hydroxylase
- C 21-alpha hydroxylase ✓
- D 3-beta hydroxysteroid dehydrogenase
Correct answer: C. 21-alpha hydroxylase
Explanation
Salt-wasting congenital adrenal hyperplasia in a neonate with virilisation of a female infant, hyponatraemia, hyperkalaemia, hypoglycaemia and grossly raised 17-hydroxyprogesterone defines classic 21-hydroxylase deficiency, accounting for about 90 percent of cases. 11-beta hydroxylase deficiency causes hypertension from deoxycorticosterone excess, not salt wasting, eliminating option A. 17-alpha hydroxylase deficiency causes hypertension and sexual infantilism. Management is glucocorticoid plus fludrocortisone and salt supplementation.
Reference: Nelson Textbook of Pediatrics, 22nd ed.
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