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 with Klinefelter syndrome may be described as XXY males or males with XXY 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 cells split unevenly to produce eggs. But it can also occur when cells split unevenly to produce sperm.

What are the symptoms?

Many men with 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.

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.

How is it treated?

Males with Klinefelter syndrome can be given testosterone, a hormone needed for sexual development. If treatment is started around the age of puberty, it can help a boy have more normal body development.

Speech therapy and educational support can help boys who have language or learning problems.

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