Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 40-21: Klinefelter Syndrome + Key Features Download Section PDF Listen +++ ++ Males with 1 extra X chromosome (XXY) Tall stature, gynecomastia, atrophic testes, infertility + Clinical Findings Download Section PDF Listen +++ ++ Boys are normal in appearance before puberty; after puberty, they have disproportionately long legs and arms, sparse body hair, a female escutcheon, gynecomastia, and small testes Infertility resulting from azoospermia; the seminiferous tubules are hyalinized Mental impairment is somewhat more common than in the general population, and many have learning problems Higher risk of osteoporosis, breast cancer, and diabetes mellitus + Diagnosis Download Section PDF Listen +++ ++ Low serum testosterone Karyotype is typically 47, XXY but other sex chromosome anomalies cause variations of Klinefelter syndrome Screening for cancer (especially of the breast), deep vein thrombosis, and glucose intolerance is indicated + Treatment Download Section PDF Listen +++ ++ Testosterone administration is advisable after puberty but will not restore fertility Intracytoplasmic sperm injection is possible using sperm obtained by testicular extraction