Klinefelter’s Syndrome (47,XXY)
Print Friendly, PDF & Email

almostadoctor app banner for android and iOS almostadoctor iPhone, iPad and android apps almostadoctor iOS app almostadoctor android app

Klinefelter’s syndrome is the presence of an extra X chromosome in males to give (47,XXY). Sometimes it may also be (48, XXYY) or (49, XXXY). Occasionally there is mosaicism with some cells having 46, XY and some having 47, XXY. Symptoms are generally most severe in cases of 49, XXXY and least severe in those with mosaicism.

Klinefelter’s Syndrome is named after Dr Harry Klinefelter at Massachusetts General Hospital in the 1940s who described a series of patients with a specific set of clinical features:

  • Tall height
  • Small testes
  • Unable to produce sperm
  • Gynaecomastia
  • Little facial or body hair
  • There may also be learning disability in more severe cases



  • 1 in 660 male live births
  • The most common sex chromosome disorder
  • Often is goes undiagnosed, or is not diagnosed until adulthood – for example when conducting fertility testing for a couple who are struggling to conceive

Clinical features

Signs of Klinefelter's syndrome
Signs of Klinefelter’s syndrome
Usually diagnosed in childhood when there is:
  • Clumsyness
  • Learning difficulties (usually mild)
  • Typically intellectual ability is reduced y 10-20 IQ points, but still within the normal range. More susceptible to behavioural and psychological problems.
  • Self obsessed behaviour


  • Taller than average
    • Long legs
    • Narrow shoulders
    • Wide hips
  • Long limbs
  • Gynaecomastia + Infertility + small soft testes (Hypogonadism) (30% of cases)
  • ↑ Risk of
  • Most patients are infertile – there is a lack of sperm in the semen (azoospermia)


  • Can be diagnosed antenatally with amniocentesis or chorionic villus sampling
  • Reproductive hormonal panel may be abnormal
    • Testosterone ↔ or ↑
    • FSH ↑
    • LH ↑
  • Diagnosis is confirmed by chromosomal analysis (karyotyping)

Complications and associations

Klinefelter’s syndrome is associated with increased risk for several other disorders, including:

The average lifespan is slightly less than the general population – by around 2 years – usually due to the increased incidence of the above associated diseases.


Testosterone – is often given from puberty onwards, and helps the development of secondary sexual characteristics. It also reduces the long-term risk of many of the long term complications and associations.

However, puberty is often normal in most cases.

  • Also helps to increase muscle mass and increase growth of facial hair and body hair
Fertility treatment
  • Injection of sperm into the egg has reportedly been successful

Plastic surgery

  • May be performed for gynaecomastia


  • Extra X chromosome
  • Equal chance of inheritance from mother or father
    • Maternal cases often associated with advancing maternal age
  • Small proportion of cases are due to mosaicism
  • >2 X chromosomes are sometimes present. These cases are associated with more severe learning difficulties, and more pronounced features of Klinefelter’s.


Read more about our sources

Related Articles

Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

Leave a Reply