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Causes
By Mayo Clinic staffKlinefelter syndrome occurs as a result of a random error that causes a male to be born with an extra sex chromosome. Of the 46 human chromosomes, the two sex chromosomes determine a person's gender. In females, both sex chromosomes are X (written as XX). Males have an X and a Y sex chromosome (XY).
Most often, Klinefelter syndrome occurs because of one extra copy of the X chromosome in each cell (XXY). Extra copies of genes on the X chromosome can interfere with male sexual development and fertility. Some males with Klinefelter syndrome have the extra X chromosome only in some of their cells (mosaic Klinefelter syndrome). Rarely, a more severe form of Klinefelter can occur if a male has more than one extra copy of the X chromosome.
Klinefelter syndrome isn't an inherited condition. Rather, the additional sex chromosome results from a random error during the formation of the egg or sperm or after conception.
- Bock R. Understanding Klinefelter syndrome: A guide for XXY males and their families. National Institute of Child Health & Human Development. http://www.nichd.nih.gov/publications/pubs/klinefelter.cfm. Accessed Aug. 30, 2010.
- Zeger M, et al. Effect of ascertainment and genetic features on the phenotype of Klinefelter syndrome. Journal of Pediatrics. 2008;152:716.
- Klinefelter syndrome. Genetics Home Reference. http://www.ghr.nlm.nih.gov/condition/klinefelter-syndrome. Accessed Aug. 30, 2010.
- Klinefelter syndrome. National Institute of Child Health & Human Development. http://www.nichd.nih.gov/health/topics/klinefelter_syndrome.cfm. Accessed Aug. 30, 2010.
- Ramasamy R, et al. Successful fertility treatment for Klinefelter's syndrome. Journal of Urology. 2009;182:1108.
- Radicioni AF, et al. Strategies and advantages of early diagnosis in Klinefelter's syndrome. Molecular Human Reproduction. 2010;16:434.
- Bruining H, et al. Psychiatric characteristics in a self-selected sample of boys with Klinefelter syndrome. Pediatrics. 2009;123:e865.
- Sex chromosome anomalies. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec19/ch294/ch294g.html. Accessed Sept. 23, 2010.
- Wattendorf DJ, et al. Klinefelter syndrome. American Family Physician. 2005;72:2259.
- Klinefelter syndrome. The Hormone Foundation. http://www.hormone.org/upload/Klinefelter-Bilingual-WEB.pdf. Accessed Aug. 30, 2010.
- Learning about Klinefelter syndrome. National Human Genome Research Institute. http://www.genome.gov/pfv.cfm?pageID=19519068. Accessed Aug. 30, 2010.
- Snyder PJ. Causes of primary hypogonadism in males. http://www.uptodate.com/home/index.html. Accessed Aug. 30, 2010.
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