XXY (Klinefelter syndrome)
Causes of Klinefelter syndrome
Klinefelter syndrome is caused by an additional X chromosome.
This chromosome carries extra copies of genes, which interfere with the development of the testicles and mean they produce less testosterone (male sex hormone) than usual.
The extra genetic information may either be carried in every cell in the body or it may only affect some cells (known as mosaic Klinefelter syndrome).
Klinefelter syndrome isn't directly inherited the additional X chromosome occurs as a result of either the mother's egg or the father's sperm having the extra X chromosome (an equal chance of this happening in either), so after conception the chromosome pattern is XXY rather than XY.
This change in the egg or sperm seems to happen randomly. If you have a son with the condition, the chances of this happening again are very small.
However, the risk of a woman having a son with Klinefelter syndrome may be slightly higher if the mother is over 35 years of age.
Medically Reviewed by a doctor on 21 Dez 2018
Introduction
Read about Klinefelter syndrome - a condition in which male babies are born with an extra X chromosome. Find out about the symptoms, causes and treatments.
Symptoms of Klinefelter syndrome
Klinefelter syndrome doesn't usually cause any obvious symptoms early in childhood, and even the later symptoms may be difficult to spot. Many boys and men don't realise they have it. Possible featu
Health issues in Klinefelter syndrome
Most boys and men with Klinefelter syndrome will not be significantly affected and can live normal, healthy lives. Infertility tends to be the main problem, although there are treatments that can hel
Causes of Klinefelter syndrome
Klinefelter syndrome is caused by an additional X chromosome. This chromosome carries extra copies of genes, which interfere with the development of the testicles and mean they produce less testoster
Testing for Klinefelter syndrome
See your GP if you have concerns about your son's development or you notice any troubling symptoms of Klinefelter syndrome in yourself or your son. Klinefelter syndrome isn't necessarily anything ser
Treatments for Klinefelter syndrome
There's no cure for Klinefelter syndrome, but some of the problems associated with the condition can be treated if necessary. Possible treatments include: testosterone replacement therapy(see below
More informationand support
If you or your son has been diagnosed with Klinefelter syndrome, you might find it useful to find out more about it and get in touch with others affected by it. The following websites may be able to
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