XXY (Klinefelter syndrome)
Klinefelter syndrome (sometimes called Klinefelter's, KS or XXY) is where boys and men are born with an extra X chromosome.
Chromosomes are packages of genes found in every cell in the body. Two types of chromosome, called the sex chromosomes, determine the genetic sex of a baby. These are named either X or Y.
Usually, a female baby has two X chromosomes (XX) and a male has one X and one Y (XY). But in Klinefelter syndrome, a boy is born with an extra copy of the X chromosome (XXY).
The X chromosome is not a "female" chromosome and is present in everyone. The presence of a Y chromosome denotes male sex.
Boys and men with Klinefelter syndrome are still genetically male, and often will not realise they have this extra chromosome, but occasionally it can cause problems that may require treatment.
Klinefelter syndrome is quite common, affecting around 1 in every 660 males.
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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.
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
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
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
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
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
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