Skip to Content

Klinefelter syndrome

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

Causes of Klinefelter syndrome

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.

Klinefelter syndrome 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

Tests and Exams

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 of Klinefelter syndrome

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) --

National Institute of Health, National Human Genome Research Institute --

Potential 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 Health 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.


Bacino CA. Cytogenetics. In: Kliegman RM, Stanton BF, St. Geme J III, Schor N, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 76.

Review Date: 11/26/2014
Reviewed By: Chad Haldeman-Englert, MD, FACMG, Wake Forest 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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- 2015 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.