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Klinefelter Syndrome

Klinefelter Syndrome

Klinefelter syndrome is due to an extra copy of an X chromosome in males (47,XXY).  Adult males have hypergonadotrophic hypo-gonadism and are invariably infertile.  However, lifespan is normal and many males may never be diagnosed. 


  • Prevalence is ~1/600–1/800 male births.
  • There is a significant maternal age effect with 1/300 at maternal age 43 years.

Clinical presentation

  • 47,XXY may present antenatally following chorionic villous sampling (CVS) or amniocentesis.
  • Babies appear normal
  • Increased incidence of undescended testes
  • Delayed puberty
  • Gynaecomastia
  • Infertility

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Physical signs

  • Males tend to have a taller final height (186cm 47,XXY vs. 176cm 46,XY)
  • Gynaecomastia
  • Increased carrying angle
  • Centripetal obesity
  • Hypogonadism
  • Normal intelligence

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  • IQ: usually only lower by 10-15 points compared to siblings. Overall intelligence is normal as an adult although ~60% will need some degree of additional educational help.  The majority of patients tend to be passive and good natured.
  • Cancer risk: there is no good evidence for a general increased risk of cancer although there is a 3% risk increase in breast cancer.  There is a <1% risk of primary germ cell tumour.
  • In adult life there is an increased risk of diabetes and cardio-vascular disease.
  • Hypogonadism: delayed puberty, gynaecomastia, infertility
  • Osteoporosis

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