Klinefelter syndrome is a condition that occurs in men as a result of an extra X chromosome. The most common symptom is infertility.

Humans have 46 chromosomes, which contain all of a person’s genes and DNA. Two of these chromosomes, the sex chromosomes, determine a person’s gender. Both of the sex chromosomes in females are called X chromosomes. (This is written as XX.) Males have an X and a Y chromosome (written as XY). The two sex chromosomes help a person develop fertility and the sexual characteristics of their gender.

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 patient may have the following signs:

• Small, firm testicles
• Small penis
• Sparse pubic, armpit, and facial hair
• Sexual problems
• Enlarged breasts (called gynecomastia)
• Tall stature
• Abnormal body proportions (long legs, short trunk)

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

The following test results may be found:

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

Testosterone therapy can achieve the following:

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

Most patients are not able to father children. However, there are some cases of men with an extra X fathering healthy offspring, sometimes with the aide of infertility specialists.

The Klinefelter Syndrome Association can be reached at PO Box 119, Roseville, CA, 95678-0119.

Most patients can expect a normal, productive life. Social and educational supports can help patients reach their potential.

The syndrome is associated with an increased risk of breast cancer, extragonadal germ cell tumor (a rare tumor), lung disease, varicose veins, and osteoporosis. There is also an increased risk for autoimmune disorder such as lupus, rheumatoid arthritis, and Sjogren's syndrome.

Learning disabilities are common, despite normal or high IQ. The risks of dyslexia, attention deficient hyperactivity disorder, and depression may be higher.

Taurodontism, which is when the teeth have enlarged pulp and surface thinning, 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 fails to develop secondary sexual characteristics at puberty

A genetics counselor can help evaluate or explain abnormal chromosome findings. The patient may also wish to consult with an endocrinologist and infertility specialist.