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 1 extra X chromosome.
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.
Most men with KS do not have symptoms. When KS does develop, it usually goes undetected until puberty or sometimes much later.
Babies may have lower birth weight, or slower muscle and motor development.
Children or adults may have:
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. Diagnosis of KS may be found incidentally. For example:
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:
There are no current guidelines to prevent KS. If you are pregnant, talk to your doctor about prenatal care and screening tests.
Klinefelter Syndrome and Associates
National Institute of Child Health and Human Development
Canadian Psychiatric Association
Canadian Psychological Association
Klinefelter syndrome. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T116877/Klinefelter-syndrome. Updated April 7, 2016. Accessed September 28, 2016.
Tell me about 47, XXY. Klinefelter Syndrome and Associates website. Available at:
http://www.genetic.org/Knowledge/WhatAreXYChromosomeVariations/Tellmeabout47,XXY.aspx. Accessed June 6, 2016.
Klinefelter syndrome (KS): Overview. National Institute of Child Health and Human Development website. Available at:
Updated October 25, 2013. Accessed June 6, 2016.
Last reviewed June 2016 by Kari Kassir, MD
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