American Urological Association - Klinefelter's Syndrome
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Klinefelter's Syndrome

  • Characterized by an abnormal number of X chromosomes (80% with 47XXY) and primary gonadal insufficiency.
  • Frequency: 1/1000-1400 live male births; 1/100 patients in mental institutions; and 3.4/100 infertile men.
  • Clinical:
    • Eunuchoid appearance with increased stature and small to normal-sized, well developed testes.
    • Incomplete virilization.
    • Gynecomastia.
    • Mental retardation, speech difficulties.
  • Histology:
    • Small hyalinized seminiferous tubules.
    • Pseudoadenomatous clusters of Leydig cells – these cells only appear to be increased in number, though, because the decreased testicular volume.
  • Associations: increased incidence of extragonadal germ cell tumors (mediastinum>pineal gland, CNS, retroperitoneum) as well as hypopituitarism.