A 3-day-old neonate with a 46,XY karyotype presents with completely female external genitalia, no palpable gonads, and normal electrolytes. Ultrasound shows no Müllerian structures (no uterus, no fallopian tubes). Serum testosterone is low but rises appropriately after hCG stimulation. What is the most likely diagnosis?

• A Complete androgen insensitivity syndrome
• B 5-alpha reductase deficiency
• C Swyer syndrome (46,XY complete gonadal dysgenesis)
• D Leydig cell hypoplasia ✓

Explanation

Leydig cell hypoplasia results from LH/hCG receptor mutations causing failed fetal Leydig cell differentiation. The 46,XY infant has female external genitalia (no androgen effect), no Müllerian structures (AMH from Sertoli cells is present), and testosterone rises minimally but some response to hCG may occur in partial forms. Complete androgen insensitivity also presents with female phenotype but typically has undescended testes with normal-to-high testosterone and preserved Müllerian absence. Swyer syndrome shows streak gonads and Müllerian structures are present. 5-alpha reductase deficiency causes ambiguous genitalia with virilization at puberty and normal testosterone but low DHT.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.