What is the karyotype for Klinefelter syndrome?

Updated: Mar 23, 2020
  • Author: Germaine L Defendi, MD, MS, FAAP; Chief Editor: Luis O Rohena, MD, MS, FAAP, FACMG  more...
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The most common karyotype is 47,XXY, which accounts for 80-90% of all cases. Mosaicism (46,XY/47,XXY) is observed in about 10% of cases. Other variant karyotypes, including 48,XXYY; 48,XXXY; 49,XXXYY; and 49,XXXXY, are rare.

  • The mosaic forms of Klinefelter syndrome are due to mitotic nondisjunction after fertilization of the zygote. These forms can arise from a 46,XY zygote or a 47,XXY zygote.

  • Variant forms of Klinefelter syndrome include 48,XXXY; 49,XXXXY; 48,XXYY; and 49,XXXYY.

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