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Klinefelter Syndrome - Topic Overview

What is Klinefelter syndrome?

Klinefelter syndrome is a genetic disorder that affects males. Klinefelter syndrome occurs when a boy is born with one or more extra X chromosomes. Most males have one Y and one X chromosome. Having extra X chromosomes can cause a male to have some physical traits unusual for males.

Many men with an extra X chromosome are not aware that they have it, and they lead normal lives. Males who have Klinefelter syndrome may be described as X-Y males or males with X-Y syndrome. Klinefelter syndrome occurs in about 1 out of 1,000 males.

What causes Klinefelter syndrome?

The presence of an extra X chromosome in males most often occurs when the genetic material in the egg splits unevenly. But it can also occur when the genetic material in the sperm splits unevenly. Even though Klinefelter syndrome is a genetic disorder, it is not passed down through families. So, parents who have a child with Klinefelter syndrome are not any more likely than other couples to have another child with the condition.

What are the symptoms?

Many men who have Klinefelter syndrome do not have obvious symptoms. Others have sparse body hair, enlarged breasts, and wide hips. In almost all men the testicles remain small. In some men the penis does not reach adult size. Their voices may not be as deep. They usually cannot father children. But they can have a normal sex life.

Some boys with Klinefelter syndrome have language and learning problems.

See a picture of a male with Klinefelter syndrome camera.gif.

How is Klinefelter syndrome diagnosed?

Klinefelter syndrome usually is not diagnosed until the time of puberty. At this point, the boy's testicles fail to grow normally and you may start to notice other symptoms.

To find out if your son has Klinefelter syndrome, your doctor will ask questions about his past health, do a physical exam, and order a chromosome test called a karyotype.

Klinefelter syndrome can be detected before birth (prenatally) through genetic tests on cells collected from amniocentesis or chorionic villus sampling (CVS). But this is not routinely done.

In adult men, lab tests in addition to a karyotype may be done, such as hormone tests or a semen analysis, if Klinefelter syndrome is suspected.

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