A newborn XY infant has bowed femurs, hypoplastic scapulae, and sex reversal with female external genitalia despite a 46,XY karyotype. The single gene most likely mutated normally functions both in chondrogenesis and, downstream of SRY, in:

• A Regression of the mesonephric ducts
• B Primordial germ cell migration from the yolk sac
• C Sertoli cell differentiation of the indifferent gonad ✓
• D Fusion of the paramesonephric ducts

Explanation

SOX9 mutations cause campomelic dysplasia, combining bowed long bones and hypoplastic scapulae from defective chondrogenesis with XY gonadal dysgenesis. SOX9 is a direct SRY target in pre-Sertoli cells and is essential for Sertoli differentiation and AMH production; without it, testes fail to form and the phenotype defaults toward female. Primordial germ cells reach the gonad independently of SOX9, and duct regression or fusion depend on AMH and testosterone rather than on SOX9 itself.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.