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Klinefelter syndrome is the presence of an extra X chromosome in a male.
47 X-X-Y syndrome
Causes, incidence, and risk factors
Most people have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two sex chromosomes determine if you become a boy or a girl. Girls normally have two XX chromosomes. Boys normally have an X and a Y chromosome.
Klinefelter syndrome is when a boy is born with at least one extra X chromosome. Usually, this occurs due to one extra X. This would be written as XXY.
Klinefelter syndrome occurs in about 1 out of 500 - 1,000 baby boys. Women who get pregnant after age 35 are slightly more likely to have a boy with this syndrome than younger women.
- Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
- Abnormally large breasts (gynecomastia)
- Sexual problems
- Less than normal amount of pubic, armpit, and facial hair
- Small, firm testicles
- Tall height
Signs and tests
Klinefelter syndrome may first be diagnosed when a man comes to the doctor because of infertility. Infertity is the most common symptom.
The following tests may be performed:
Blood tests will be done to check hormone levels including:
Testosterone therapy may be prescribed. This can help:
Most men with this syndrome are not able to get a woman pregnant. However, an infertility specialist may be able to help. A special doctor called an endocrinologist may also be helpful.
The American Association for Klinefelter Syndrome Information and Support (AAKSIS) - www.aaksis.org
Enlarged teeth with a thinning surface is very common in Klinefelter syndrome. This is called taurodontism. This can be seen on dental x-rays.
Klinefelter syndrome also increases your risk of:
Calling your health care provider
Call for an appointment with your health care provider if your son does not develop secondary sexual characteristics at puberty. This includes facial hair growth and a deepening of the voice.
A genetics counselor can provide information about this condition and direct you to support groups in your area.
Bacino CA, Lee B. Cytogenetics. In:Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds.
Nelson Textbookof Pediatrics.19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 74.
- Last reviewed on 11/2/2012
- Chad Haldeman-Englert, MD, FACMG, Wake Forest School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon.
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This page was last updated: April 14, 2014