Klinefelter syndrome is a genetic condition that occurs in males when they have an extra X chromosome.
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.
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:
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.
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:
- Attention deficient hyperactivity disorder
- Autoimmune disorders, such as lupus, rheumatoid arthritis, and Sjogren syndrome
- Breast cancer in men
- Learning disabilities, including dyslexia, which affects reading
- A rare type of tumor called an extragonadal germ cell tumor
- Lung disease
- Varicose veins
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.
47 X-X-Y syndrome; XXY syndrome; XXY trisomy; 47,XXY/46,XY; Mosaic syndrome; Poly-X Klinefelter syndrome
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
Updated 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.