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This revision: 26th April 2013 .
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Klinefelter syndrome or Klinefelter's syndrome, also 47,XXY or XXY syndrome, is a genetic disorder in which there is at least one extra X chromosome to a standard human male karyotype, for a total of 47 chromosomes rather than the 46 found in genetically normal humans.[1] While females have an XX chromosomal makeup, and males an XY, individuals with Klinefelter syndrome have at least two X chromosomes and at least one Y chromosome.[2]

Because of the extra chromosome, individuals with the condition are usually referred to as "XXY males", or "47,XXY males".[3]

This chromosome constitution (karyotype) exists in roughly between 1:500 to 1:1000 live male births[4][5] but many of these people may not show symptoms. If the physical traits associated with the syndrome become apparent, they normally appear after the onset of puberty.[6]

Cognitive and developmental

Some degree of language learning or reading impairment may be present,[13] and neuropsychological testing often reveals deficits in executive functions, although these deficits can often be overcome through early intervention.[14]

There may also be delays in motor development which can be addressed through occupational therapy.[15] XXY males may sit up, crawl, and walk later than other infants; they may also struggle in school, both academically and with sports.[4]

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