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For further information, see CMDT Part 40-22: Klinefelter Syndrome

Key Features

  • Males with 1 extra X chromosome (XXY)

  • Tall stature, gynecomastia, atrophic testes, infertility

Clinical Findings

  • 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 retardation is somewhat more common than in the general population, and many have learning problems

  • Higher risk of osteoporosis, breast cancer, and diabetes mellitus


  • 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 venous thrombosis, and glucose intolerance is indicated


  • Testosterone administration is advisable after puberty but will not restore fertility

  • Intracytoplasmic sperm injection is possible using sperm obtained by testicular extraction

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