What are the diagnostic postnatal tests 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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Karyotype analysis on peripheral blood lymphocytes, the XCAT-KS buccal swab test, fluorescence in-situ hybridization (FISH), and microarrays are options for postnatal diagnostic testing.

The 47,XXY karyotype is found in 80-90% of males who are diagnosed with Klinefelter syndrome. About 10% of patients have mosaicism (more than one cell line): 46,XY/47,XXY; 46,XY/48,XXXY; and 47,XXY/48,XXXY. Remaining cases include karyotype variants such as 48,XXYY; 48,XXXY; 49,XXXYY; and 49,XXXXY. About 1% of cases are due to a structurally abnormal X in addition to a normal X and Y, such as 47,X,i(Xq)Y and 47,X,del(X)Y.

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