A newborn presents with hypospadias, cryptorchidism, and bifid scrotum. Testing reveals 46,XY karyotype with a markedly elevated LH and testosterone but absent dihydrotestosterone (DHT). The likely embryological cause is:
- A 5-alpha reductase type 2 deficiency — DHT cannot be made from testosterone for external genital virilisation ✓
- B Complete androgen insensitivity syndrome (CAIS) — testosterone receptor absent
- C 17-beta hydroxysteroid dehydrogenase deficiency
- D Persistent Müllerian duct syndrome — anti-Müllerian hormone receptor deficiency
Explanation
5-alpha reductase type 2 (encoded by SRD5A2 gene) converts testosterone to DHT in the urogenital sinus, genital tubercle, and labioscrotal folds. DHT is required for masculinisation of the external genitalia (formation of penis and scrotum from genital tubercle and labioscrotal folds). Without DHT, the external genitalia virilise only incompletely (hypospadias, bifid scrotum, small phallus). The wolffian ducts (epididymis, vas deferens) develop normally because they respond to testosterone directly. At puberty, a surge in testosterone produces partial virilisation. CAIS would present as a phenotypic female (46,XY) because testosterone itself cannot signal via the absent receptor.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.