Klinefelter's syndrome is a genetic condition that only affects males. Affected males have an extra X chromosome.
Males with Klinefelter's syndrome have small testicles (testes) which do not produce enough of the male hormone testosterone before birth and during puberty. This lack of testosterone means that during puberty, the normal male sexual characteristics do not develop fully. There is reduced facial and pubic hair, and some breast tissue often develops. The lack of testosterone is also responsible for other symptoms, including infertility.
Treatment includes testosterone replacement. This can help improve some of the symptoms but does not have an effect on fertility. The majority of men with Klinefelter's syndrome lead an independent life, forming relationships and getting a normal job. They also have a normal lifespan.
In general, each cell in your body contains 46 chromosomes arranged in 23 pairs. One chromosome from each pair is inherited from your mother and the other is inherited from your father. One of these chromosome pairs is known as the sex chromosomes because this pair of chromosomes determines our sex.
Females have two of the same kind of sex chromosome (XX). Males have two different sex chromosomes (XY). The Y chromosome contains the male determining genes. So a female normally has 46, XX chromosomes and a male normally has 46, XY.
In KS, males have an extra X chromosome. It is a genetic problem that only affects boys and men. It is a sex chromosome trisomy. Instead of being 46, XY, men or boys with KS are usually 47, XXY.