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Klinefelter syndrome

Contents of this page:

Alternative Names   

47 X-X-Y syndrome

Definition    Return to top

Klinefelter syndrome is the presence of an extra X chromosome in a male.

Causes    Return to top

Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males normally have an X and a Y chromosome (written as XY).

Klinefelter syndrome is one of a group of sex chromosome problems. It results in males who have at least one extra X chromosome. Usually, this occurs due to one extra X (written as XXY).

Klinefelter syndrome is found in about 1 out of every 500 - 1,000 newborn males. Women who have pregnancies after age 35 are slightly more likely to have a boy with this syndrome than younger women.

Symptoms    Return to top

The most common symptom is infertility. Other symptoms may include:

Exams and Tests    Return to top

Adults may come to the doctor because of infertility. School-age children may be brought in to because of learning problems.

The following tests may be performed:

Treatment    Return to top

Testosterone therapy may be prescribed. This can help:

Most men with this syndrome are not able to father children. However, some men have been able to have children. An infertility specialist may be able to help.

Support Groups    Return to top

The American Association for Klinefelter Syndrome Information and Support (AAKSIS) -

Outlook (Prognosis)    Return to top

Most patients have a normal, productive life.

Possible Complications    Return to top

The syndrome increases the risk of:

Enlarged teeth with a thinning surface (taurodontism) is very common in Klinefelter syndrome. It can be diagnosed by dental x-rays.

When to Contact a Medical Professional    Return to top

Call for an appointment with your health care provider if a boy does not develop secondary sexual characteristics at puberty.

A genetics counselor can provide information about this condition, and help explain abnormal chromosome findings and possible complications. The counselor will also be familiar with local and national support groups.

An endocrinologist and infertility specialist may also be helpful.

Update Date: 10/15/2008

Updated by: Diana Chambers, MS, EdD, Certified Genetics Counselor (ABMG), Charter Member of the ABGC, University of Tennessee, Memphis, TN. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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