Criteria

Karyotype analysis

A full chromosomal karyotype is the sole confirming criterion. Klinefelter syndrome (KS) is confirmed by a genetic karyotype of 47,XXY.[1]​[2]​[3]​

  • Around 90% of individuals with KS have the 47,XXY karyotype (47 chromosomes, with an extra X), with the remainder having mosaic karyotypes such as 46,XY/47,XXY (i.e., the extra X chromosome is present in some cells but other cells have the typical male karyotype of 46,XY).[4]​

Karyotype 47,XXY is specific to KS; other sex chromosomal karyotypes (e.g., 47,XYY; 48,XXXY and 48,XXYY; 49,XXXXY) are different conditions with their own phenotypes.[14]​​[20]​​[33]

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