Klinefelter's syndrome overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Klinefelter's syndrome is a condition caused by a chromosome aneuploidy. Affected males have an extra X chromosome. The principal effects are the development of small testicles and reduced fertility. A variety of other physical, behavioral differences, and problems are common. The severity varies and many boys and men with the condition have few detectable symptoms. Because of the extra chromosome, individuals with the condition are usually referred to as "XXY Males", or "47, XXY Males".[1]

In humans, 47,XXY is the most common sex chromosome aneuploidy in males[2] and the second most common condition caused by the presence of extra chromosomes. Other mammals also have the XXY syndrome, including mice.[3]


  1. Bock, Robert (1993). "Understanding Klinefelter Syndrome: A Guide for XXY Males and their Families". NIH Pub. No. 93-3202. Office of Research Reporting, NICHD. Retrieved 2007-04-07. Unknown parameter |month= ignored (help)
  2. James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. p 549. ISBN 0-7216-2921-0.
  3. Russell, Liane Brauch (9 June 1961). "Genetics of Mammalian Sex Chromosomes MOUSE STUDIES THROW LIGHT ON THE FUNCTIONS AND ON THE OCCASIONALLY ABERRANT BEHAVIOR OF SEX CHROMOSOMES". Science. 133 (3467): 1795–1803. doi:10.1126/science.133.3467.1795.

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