Klinefelter syndrome
47,XXY
Also known as: 47 XXY
47,XXY is the karyotype of Klinefelter syndrome, an extra X chromosome in a male. It is the most common sex chromosome aneuploidy, and small firm testes with infertility are typical.
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What the notation means
47- total chromosome count (normal is 46)
XXY- sex chromosomes: two X + one Y
Clinical notes
Klinefelter syndrome (47,XXY and variants)
An extra X in a male (≥1 Y with ≥2 X); 47,XXY is classic, with 48,XXXY and 48,XXYY as higher-grade variants. Tall stature, small firm testes, gynecomastia, infertility, low testosterone. The extra X (or Xs) inactivate as Barr bodies.