Laurie Rosenblum, MPH
Klinefelter syndrome (KS) occurs in some men who have more than one X chromosome (XXY).
Males usually inherit a single X chromosome from their mother and a single Y chromosome from their father. Males with KS get at least one extra X chromosome.
A risk factor is something that increases your chance of KS. Women over age 35 may have a slightly increased chance of having a child with KS. There are no other known risk factors for this disorder.
XXY occurs in approximately 1 out of 580 live male births, but many men with it do not develop KS. When KS does develop, it usually goes undetected until puberty or sometimes much later.
Characteristics may include:
Men with KS have an increased risk of:
A test called a karyotype is used to diagnose KS. In the case of KS, there are usually 47 chromosomes rather than the normal 46.
Many men with XXY do not know they have the condition. The diagnosis may be found:
Treatment of KS includes:
The main treatment is testosterone . When boys with KS are 10-12 years old, their hormone levels are checked yearly. If testosterone levels are low, then treatment may be helpful. Men diagnosed may also benefit from taking the hormone. However, testosterone cannot reverse infertility.
The benefits of testosterone include:
This therapy should begin in early childhood to avoid social and school learning problems. Treatment may involve:
Currently, there are no known ways of preventing KS.
Klinefelter Syndrome and Associates
National Institute of Child Health & Human Development
Canadian Psychiatric Association
Canadian Psychological Association
Klinefelter syndrome. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed. Updated February 28, 2013. Accessed October 11, 2011.
Tell me about 47, XXY. Klinefelter Syndrome and Associates website. Available at:
http://www.genetic.org/knowledge/support/action/199/#Brief%20Introduction%20to%20Klinefelter%20syndrome. Accessed August 20, 2013.
Klinefelter syndrome: overview. National Institute of Child Health & Human Development website. Available at:
Updated April 3, 2013. Accessed August 20, 2013.
Last reviewed August 2013 by Kari Kassir, MD; Michael Woods, MD
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