Poly-X Klinefelter syndrome: General Information


Category of poly-X Klinefelter syndrome:

  • Syndrome

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Prevalence of Poly-X Klinefelter syndrome

The likelihood of a third or fourth X is much rarer: 2

Prevalence of Klinefelter syndrome variants

Number of extra X chromosomes: Number of newborn males with the condition

One (XXY): 1 in 500

Two (XXXY): 1 in 50,000

Three (XXXXY): 1 in 85,000 to 100,000

Source: NICHD (NIH)2

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  1. Source: NCI Thesaurus
  2. Source: NICHD (NIH): nichd.nih.gov/ health/ topics/ klinefelter/ conditioninfo/ Pages/ risk.aspx

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