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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)
• Infertility
• Sexual problems
• Less than normal amount of pubic, armpit, and facial hair
• Small, firm testicles
• Tall height

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:

• Karyotyping
• Semen count

Blood tests will be done to check hormone levels including:

• Estradiol, a type of estrogen
• Follicle stimulating hormone
• Luteinizing hormone
• Testosterone

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
• Depression
• Learning disabilities, including dyslexia, which affects reading
• A rare type of tumor called an extragonadal germ cell tumor
• Lung disease
• Osteoporosis
• Varicose veins

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.