Klinefelter's Syndrome



What is Klinefelter's?

Klinefelter's Syndrome occurs only in men who carry an extra X chromosome (XXY, 47 MALE) (XXY CONDITION)


About Klinefelter's Syndrome:

Klinefelter's Syndrome was discovered by Harry Klinefelter.Klinefelter's Syndrome is a disorder that only affects males. Males normally have an X chromosome and a Y chromosome (XY). However, males who have Klinefelter's Syndrome have an extra X chromosome (XXY), giving them a total of 47 instead of the normal 46 chromosomes.
external image kleinfelter_karyotype.jpg

People with this disorder develop as males with subtle characteristics that mostly become apparent during puberty. Symptoms can also show as early as childhood (such as being weaker than the average child and having a delayed learning ability and poor coordination). If these do not show, then they can be easily seen in adulthood, when a man has trouble impregnating a woman. Males with Klinefelter’s are often tall and usually don't develop secondary sex characteristics, such as facial hair, underarm and pubic hair. The extra X chromosome primarily affects the testes, which produce sperm and the male hormone. Lack of this hormone (testosterone) makes men with Klinefelter's Syndrome infertile, or not able to have children.
There are also different variations of this disorder, such as the XY/XXY mosaic, where some cells in the body contain an extra X chromosome, while the rest have the regular XY chromosome. This variation can sometimes allow males to be fertile, if having enough cells that normally function in the testes. Sometimes, there can be up to three extra X chromosomes. It has also been reported that some males contain both an extra X and Y chromosome, but these scenarios are extremely rare. In these cases, the symptoms tend to be exaggerated, such as moderate to severe mental retardation.

How is this disorder inherited?

Klinefelter’s Syndrome is not genetically inherited. It normally happens randomly during the formation of reproductive cells. It is caused by a mutation in meiosis called nondisjuction. Nondisjunction, the failure of chromosome pairs to separate properly during cell division, results in a gamete cell with an abnormal number of chromosomes. This is how a cell can gain one or more extra copies of the X chromosome. This disorder cannot be genetically inherited; it occurs randomly. However, women that have children at an older age (40 years or older) have a higher chance of having a son with Klinefelter's Syndrome.


  1. Klinefelter’s only affects males, never females
  2. It does not occur in one race more than others
  3. It is the most common sex disorder/chromosome abnormality
  4. Normal IQ range
  5. 1 in every 1000 males has it
  6. 1 in every 500 males has it but is not affected

external image KlinefeltersIMG.jpgSymptoms of Klinefelter's:

  • Infertility (cannot get a woman pregnant)
  • Low levels of testosterone
  • Have sparse pubic, facial, and body hair
  • Have underdeveloped muscles
  • Have enlarged breasts (gynecomastia)
  • Taller then other males in their family and have longer legsexternal image gynecomastia2.jpg
  • Narrow shoulders and wide hips
  • Smaller testicles
  • More breast tissue

  • Delayed language development
  • Speech problems
  • Reduced abilities in multi-tasking
  • Reduced abilities in impulse control and response time
  • Immature or shy/quiet behavior
  • 25%-85% of Klinefelter's patients are affected with language/speech problems

Cause, Diagnosis and Treatment:

The main cause for Klinefelter's is an extra X chromosome that is kept from an error in meiosis. This occurs in about 1 in every 500 males. It is diagnosed within fetal development, or some time during puberty or in adulthood. It can also be diagnosed by a blood test. Some men may never even be diagnosed with the condition. Klinefelter’s is treated with Testosterone Replacement Therapy (TRT). This can be used to replace the lack of testosterone in the male’s body. This therapy can be done easily once a month. TRT helps with muscle growth, deeper voice, and the help to grow hair. There are also several other forms of therapy, which can help males live normally. Currently, there is no cure for Klinefeler's, but it is possible for majority of the men with Klinefelter's to live rather normal lives, even with the disorder.
Sam F, Mahnoor U, Bryanna F, Coco C.