A 2-day-old newborn with ambiguous genitalia, hyponatremia, hyperkalemia, and hypotension is diagnosed with congenital adrenal hyperplasia. The most common enzymatic deficiency causing this presentation is:

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

Explanation

21-hydroxylase deficiency accounts for approximately 90-95% of congenital adrenal hyperplasia cases. It causes cortisol deficiency (leading to ACTH excess and ambiguous genitalia in females due to androgen excess), aldosterone deficiency (causing salt-wasting with hyponatremia, hyperkalemia, and hypotension). 11-beta-hydroxylase deficiency causes hypertension due to DOC excess. 17-alpha-hydroxylase deficiency causes hypertension and sexual infantilism.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.