Klinefelter syndrome is the presence of an extra X chromosome in a male.
47 X-X-Y syndrome
Most people have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two sex chromosomes determine if you become a boy or a girl. Girls normally have two XX chromosomes. Boys normally have an X and a Y chromosome.
Klinefelter syndrome is when a boy is born with at least one extra X chromosome. Usually, this occurs due to one extra X. This would be written as XXY.
Klinefelter syndrome occurs in about 1 out of 500 - 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.
- Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
- Abnormally large breasts (gynecomastia)
- 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. Infertity is the most common symptom.
The following tests may be performed:
Blood tests will be done to check hormone levels including:
- Estradiol, a type of estrogen
- Follicle stimulating hormone
- Luteinizing hormone
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. However, an infertility specialist may be able to help. A special doctor called an endocrinologist may also be helpful.
The American Association for Klinefelter Syndrome Information and Support (AAKSIS) - www.aaksis.org
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 your 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.
Bacino CA, Lee B. Cytogenetics. In:Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds.
Nelson Textbookof Pediatrics.19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 74.
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 A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon.
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