A newborn has ambiguous genitalia and is found to have a 46,XX karyotype with normal ovaries and elevated androgens. Serum 17-hydroxyprogesterone is markedly elevated. Which enzyme deficiency is the most likely cause?

• A 5-alpha reductase deficiency
• B 21-hydroxylase deficiency ✓
• C Aromatase deficiency
• D 17-alpha hydroxylase deficiency

Explanation

21-hydroxylase deficiency causes congenital adrenal hyperplasia (CAH), the most common cause of ambiguous genitalia in 46,XX newborns. Cortisol synthesis is blocked, shunting precursors to androgen pathways, causing virilisation. 5-alpha reductase and 17-alpha hydroxylase deficiencies cause undervirilisation in 46,XY individuals. Aromatase deficiency causes maternal virilisation during pregnancy but not classic CAH biochemistry.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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