A female neonate is born with ambiguous genitalia. Clitoral enlargement and labioscrotal fusion are noted. Serum electrolytes show Na 128 mEq/L, K 6.8 mEq/L, and glucose is 45 mg/dL. The 17-hydroxyprogesterone level is markedly elevated. The ENZYME deficiency MOST likely responsible is:

• A 11-beta hydroxylase deficiency
• B 3-beta hydroxysteroid dehydrogenase deficiency
• C 17-alpha hydroxylase deficiency
• D 21-hydroxylase (CYP21A2) deficiency ✓

Explanation

21-hydroxylase deficiency accounts for approximately 90–95% of all congenital adrenal hyperplasia (CAH) cases. It impairs cortisol and aldosterone synthesis, causing excess ACTH stimulation, adrenal androgen overproduction, virilization in females, and (in the salt-wasting form) hyponatremia, hyperkalemia, and hypoglycemia due to aldosterone deficiency. The markedly elevated 17-hydroxyprogesterone is the diagnostic hallmark. 11-beta hydroxylase deficiency causes hypertension (not salt-wasting) due to 11-deoxycorticosterone accumulation.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.