Klinefelter syndrome (KS) also known as 47,XXY or XXY, is the set of symptoms that result from two or more X chromosomesin males. The primary feature is sterility. Often symptoms may be subtle and many people do not realize they are affected. Sometimes symptoms are more prominent and may include weaker muscles, greater height, poor coordination, less body hair, smaller genitals, breast growth, and less interest in sex. Often it is only at puberty that these symptoms are noticed. Intelligence is usually normal; however, reading difficulties and problems with speech are more common. Symptoms are typically more severe if three or more X chromosomes are present.
Klinefelter syndrome usually occurs randomly. An older mother might increase the risk slightly. The condition is not inherited from one's parents. The underlying mechanisms involves at least one extra X chromosome in addition to a Y chromosome such that there is a total of 47 or more chromosomes rather than usual 46. KS is diagnosed by the genetic test known as a karyotype.
While there is no cure, a number of treatments may help. Physical therapy, speech and language therapy, counselling, and adjustments of teaching methods may be useful. Testosterone replacement may be used in those who have significantly low levels. Enlarged breasts may be removed by surgery. About half of males affected with the help of assisted reproductive technology have a chance of having children; however, this is expensive and carries risks. Males appear to have a higher risk of breast cancer than typical but still lower than that of females. The condition has a nearly normal life expectancy.
Klinefelter syndrome is one of the most common chromosomal disorders, occurring in 1:500 to 1:1000 live male births. It is named after Harry Klinefelter who identified the condition in the 1940s. 1956 saw the identification of the extra X chromosome. Mice can also have the XXY syndrome, making them a useful research model.
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