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

Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two of these chromosomes, the 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 results in males who have at least one extra X chromosome. Usually, this occurs as a result of 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.

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

• Small, firm testicles
• Small penis
• Only a little bit of pubic, armpit, and facial hair
• Sexual problems
• Enlarged breasts ( gynecomastia)
• Tall height
• Abnormal body proportions (long legs, short trunk)

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

The following test results may be found:

• Karyotyping shows 47 XXY.
• Semen count is low.
• Serum testosterone is low.
• Serum luteinizing hormone is high.
• Serum follicle stimulating hormone is high.
• Serum estradiol levels (a type of estrogen) is high.

Testosterone therapy may be prescribed. This can help:

• Increase strength
• Improve appearance of muscles
• Grow body hair
• Improve mood and self esteem
• Increase energy and sex drive
• Improve concentration

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

Most patients have a normal, productive life.

The syndrome is associated with an increased risk of:

• Breast cancer
• Extragonadal germ cell tumor (a rare tumor)
• Lung disease
• Varicose veins
• Osteoporosis
• Autoimmune disorders such as lupus, rheumatoid arthritis, and Sjogren syndrome
• Learning disabilities, despite normal or high IQ
• Dyslexia
• Attention deficient hyperactivity disorder
• Depression

Taurodontism, which is when the teeth have enlarged pulp and a thinning surface, is very common in Klinefelter syndrome. It can be diagnosed by dental x-rays.

Call for an appointment with your health care provider if a boy does not develop secondary sexual characteristics at puberty. A genetics counselor can help explain abnormal chromosome findings. A consultation with an endocrinologist and infertility specialist may also be helpful.