Klinefelter syndrome is the presence of an extra X chromosome in a male.

47 X-X-Y syndrome

Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two XX chromosomes. Males normally have an X and a Y chromosome.

Klinefelter syndrome is one of a group of sex chromosome problems. It results in males who have 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 newborn boys. Women who get pregnant after age 35 are slightly more likely to have a boy with this syndrome than younger women.

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Klinefelter syndrome Symptoms

Review Date: 11/01/2010
Reviewed By: Chad Haldeman-Englert, MD, Wake Forest University School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)