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Klinefelter Syndrome (KS): Overview

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KS describes a set of physical, language, and social development symptoms in males who have an extra X chromosome. Its main feature is infertility. Outward signs of KS can be subtle, so symptoms often are not recognized, and may not be treated in a timely manner. The NICHD is one of many federal agencies and NIH Institutes working to understand KS, discover why it occurs, and identify and treat its symptoms.

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Common Name

  • Klinefelter syndrome

Medical or Scientific Names

  • Klinefelter syndrome 
  • 47,XXY 
  • XXY syndrome or condition
  • XXY trisomy
  • 47,XXY/46,XY or mosaic syndrome (rare variation)
  • Poly-X Klinefelter syndrome, including the following rare variations: 
    • 48,XXYY (or tetrasomy)
    • 48,XXXY (or tetrasomy)
    • 49,XXXXY (or pentasomy)
Last Reviewed: 10/25/2013
Vision National Institutes of Health Home BOND National Institues of Health Home Home Storz Lab: Section on Environmental Gene Regulation Home Machner Lab: Unit on Microbial Pathogenesis Home Division of Intramural Population Health Research Home Bonifacino Lab: Section on Intracellular Protein Trafficking Home Lilly Lab: Section on Gamete Development Home Lippincott-Schwartz Lab: Section on Organelle Biology