A 46,XY infant is born with predominantly female external genitalia including a phallic structure resembling a clitoris and a blind-ending vagina. At age 12, the child develops deepening of voice, increased muscle mass, and phallic enlargement. Serum testosterone is elevated but dihydrotestosterone (DHT) is low. What is the diagnosis?

• A Complete androgen insensitivity syndrome
• B Leydig cell hypoplasia
• C 17-beta hydroxysteroid dehydrogenase deficiency
• D 5-alpha reductase deficiency ✓

Explanation

5-alpha reductase type 2 converts testosterone to DHT, which is required for external genital masculinization in utero. Deficiency causes female or ambiguous genitalia at birth, but virilization occurs at puberty when testosterone rises. The elevated testosterone with low DHT ratio is diagnostic. CAIS would show no virilization at puberty.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.