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Klinefelter syndrome

Klinefelter syndrome is a genetic condition that occurs in males when they have an extra X chromosome.

Causes

Most people have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The 2 sex chromosomes (X and Y) determine if you become a boy or a girl. Girls normally have 2 X chromosomes. Boys normally have 1 X and 1 Y chromosome.

Klinefelter syndrome results when a boy is born with at least 1 extra X chromosome. Usually, this occurs due to 1 extra X. This is written as XXY.

Klinefelter syndrome occurs in about 1 out of 500 to 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.

Symptoms

Symptoms may include any of the following:

  • Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
  • Abnormally large breasts (gynecomastia)
  • Infertility
  • Sexual problems
  • Less than normal amount of pubic, armpit, and facial hair
  • Small, firm testicles
  • Tall height

Exams and Tests

Klinefelter syndrome may first be diagnosed when a man comes to the doctor because of infertility. Infertility is the most common symptom.

The following tests may be performed:

Blood tests will be done to check hormone levels including:

Treatment

Testosterone therapy may be prescribed. This can help:

  • Grow body hair
  • Improve appearance of muscles
  • Improve concentration
  • Improve mood and self esteem
  • Increase energy and sex drive
  • Increase strength

Most men with this syndrome are not able to get a woman pregnant. But, an infertility specialist may be able to help. Seeing a doctor called an endocrinologist may also be helpful.

Support Groups

These groups can provide more information:

The American Association for Klinefelter Syndrome Information and Support (AAKSIS) -- www.aaksis.org

National Institute of Health, National Human Genome Research Institute -- www.genome.gov/19519068

Possible Complications

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 the risk of:

When to Contact a Medical Professional

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.

Alternative Names

47 X-X-Y syndrome; XXY syndrome; XXY trisomy; 47,XXY/46,XY; Mosaic syndrome; Poly-X Klinefelter syndrome

References

Bacino CA. Cytogenetics. In: Kliegman RM, Stanton BF, St. Geme J III, Schor N, Behrman RE, eds.Nelson Textbook of Pediatrics

Update Date 11/26/2014

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