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Klinefelter syndrome

Definition:
Klinefelter syndrome is a chromosome abnormality that affects only men and causes hypogonadism.

Alternative Names:
47 X-X-Y syndrome

Causes, incidence, and risk factors:

A person's sex is determined by the X and Y chromosomes. Normally, men have an X and a Y and women have two X's. In Klinefelter syndrome, a male has two X's and a Y.

The condition is common and affects 1 in 500 men. The infant appears normal at birth, but the defect usually becomes apparent in puberty when secondary sexual characteristics fail to develop (or develop late). At this time, testicular changes occur that eventually result in infertility in the majority of those affected. Some mild cases may go undetected, with no abnormalities present except infertility.

One risk factor for this condition is the mother giving birth at an older age. In most cases, the problem develops during fetal development and is not inherited from one or both parents.



Review Date: 2/5/2003
Reviewed By: Douglas R. Stewart, M.D., Division of Medical Genetics, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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