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Klinefelter syndrome

Other Names for this Disease
  • Klinefelter's syndrome
  • XXY syndrome
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Klinefelter syndrome (KS) is a condition that may be present in an individual that has two X chromosomes and one Y chromosome (47, XXY); usually, males have one X and one Y (XY) and females have two X chromosomes (XX). Some individuals with a 47, XXY chromosome finding may have no obvious signs or symptoms of KS while others may have several features and varying degrees of cognitive, social, behavioral, and learning difficulties.[1] Because features may not be apparent until mid to late adolescence, the term “Klinefelter syndrome” is often reserved for affected adolescents and adults. Although the vast majority of boys with KS identify as males, some individuals develop atypical gender identities.[2] In adulthood, individuals with Klinefelter syndrome may have primary hypogonadism (decreased testosterone production), small testes, enlarged breast tissue (gynecomastia), tall stature, and/or other features.[1] The vast majority of males with KS are infertile, but many produce sperm and may be able to conceive with assisted reproduction. Treatment varies among individuals and may include testosterone therapy; however, this therapy may not be appropriate for all individuals.[2]
Last updated: 9/20/2013


  1. Aksglaede L, Link K, Giwercman A, Jørgensen N, Skakkebaek NE, Juul A. 47,XXY Klinefelter syndrome: clinical characteristics and age-specific recommendations for medical management. Am J Med Genet C Semin Med Genet. February 15, 2013; 163C(1):55-63.
  2. Klinefelter Syndrome: Condition Information. NICHD. November 30, 2012; Accessed 1/1/1900.
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Basic Information

  • The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) provides information related to the health of children, adults, and families. Click on the link to view information on this topic. 
  • The Genetic Alliance is an international coalition comprised of more than 600 advocacy, research and health care organizations representing millions of individuals with genetic conditions. Click on the link to view information on this topic.
  • Genetics Home Reference (GHR) contains information on Klinefelter syndrome. This website is maintained by the National Library of Medicine.
  • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
  • The National Human Genome Research Institute's (NHGRI) mission encompasses a broad range of studies aimed at understanding the structure and function of the human genome and its role in health and disease. Click on the link to view the information page on this topic.
  • The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.

In Depth Information

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  • MeSH® (Medical Subject Headings) is a terminology tool used by the National Library of Medicine. Click on the link to view information on this topic.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Klinefelter syndrome. Click on the link to view a sample search on this topic.