A 19-year-old man presents for evaluation of infertility. He is tall with eunuchoid proportions, has sparse facial hair, gynecomastia, and small firm testes. Semen analysis shows azoospermia. Serum testosterone is low with disproportionately elevated FSH and LH. The most likely karyotype is:

• A 45,X/46,XY mosaic
• B 47,XXY ✓
• C 47,XYY
• D 46,XX male

Explanation

The combination of tall stature, gynecomastia, small firm testes, azoospermia, and a hypergonadotropic pattern is diagnostic of Klinefelter syndrome, classically 47,XXY, arising from meiotic nondisjunction. Elevated gonadotropins reflect primary testicular failure with Leydig cell dysfunction. 47,XYY males are typically tall but fertile with normal testosterone and no gynecomastia. 45,X/46,XY mosaicism causes mixed gonadal dysgenesis rather than this phenotype. SRY translocation onto an X chromosome produces a phenotypic male with normal external genitalia, not hypergonadotropic hypogonadism.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.