Klinefelter syndrome 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 Klinefelter syndrome 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 Klinefelter syndrome, discover why it occurs, and identify and treat its symptoms.
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Common Name
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)