It is estimated that 1 in every 500 to 1,000 newborn males has an extra X chromosome, making Klinefelter syndrome one of the most common chromosomal disorders seen among newborns. Variants of Klinefelter syndrome (such as 48,XXXY, 49,XXXXY) are much rarer, occurring in 1 in 50,000 to 1 in 85,000 or fewer newborns.
It is suspected that Klinefelter syndrome is underdiagnosed because mild cases may not be identified. In addition, the features of this condition vary and can overlap significantly with those of other conditions.
Last updated: 10/13/2015
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