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Klinefelter syndrome (KS) also known as 47,XXY or XXY, is the set of symptoms that result from two or more X chromosomes in males.
Klinefelter syndrome is one of the most common chromosomal disorders, occurring in one to two per 1,000 live male births.
Sometimes, symptoms are more prominent and may include weaker muscles, greater height, poor coordination, less body hair, 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 (XXXY syndrome or 49,XXXXY).
Klinefelter syndrome usually occurs randomly. An older mother may have a slightly increased risk of a child with KS. The condition is not typically inherited from one's parents.
The underlying mechanisms involves at least one extra X chromosome in addition to a Y chromosome such that the total chromosome number is 47 or more rather than the usual 46. KS is diagnosed by the genetic test known as a karyotype.
While no cure is known, a number of treatments may help. Physical therapy, speech and language therapy, counselling, and adjustments of teaching methods may be useful.
It is named after Harry Klinefelter, who identified the condition in the 1940s. In 1956, identification of the extra X chromosome was first noticed.