DefinitionBy Mayo Clinic staff
Klinefelter syndrome is a genetic condition that results when a boy is born with an extra copy of the X chromosome. Klinefelter syndrome is one of the most common genetic conditions affecting males.
Klinefelter syndrome adversely affects testicular growth, and this can result in smaller than normal testicles. This can lead to lower production of the sex hormone testosterone. Klinefelter syndrome may also cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue. The effects of Klinefelter syndrome vary, and not everyone with it develops signs and symptoms.
Klinefelter syndrome often isn't diagnosed until adulthood. Most men with Klinefelter syndrome produce little or no sperm. But assisted reproductive procedures may make it possible for some men with Klinefelter syndrome to father children.
- 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.