A chromosome abnormality that affects only men and causes hypogonadism .

Alternative Names

47 X-X-Y syndrome

Causes, incidence, and risk factors

Klinefelter syndrome is caused by an extra X chromosome and affects only males. An infant appears normal at birth, but the defect usually becomes apparent in puberty when secondary sexual characteristics fail or are late to develop, and testicular changes occur that eventually result in infertility in the majority of those affected. Some mild cases may go undetected with no abnormalities present except infertility. Increased maternal age is a risk factor. It is usually a sporadic event, not inherited, that leads to the extra X chromosome.

Signs and tests

Physical examination (rectal exam) may show an enlarged prostate. A single testicle may be present in the scrotum indicating a probable undescended testicle. Tests may include:

Treatment

There is no treatment for the infertility associated with this syndrome. Testosterone therapy will improve the development of secondary sexual characteristics. The testicular changes that lead to infertility are not preventable. Gynecomastia (enlarged breast tissue) can be treated with plastic surgery if it is disfiguring. Counseling may be of benefit to people with emotional maladjustment due to sexual dysfunction and to reinforce male identity.

Support groups

Klinefelter support groups can be accessed through www.geneticalliance.org .

Expectations (prognosis)

Infertility should be discussed with an infertility specialist. With testosterone therapy, a more normal appearance is the general rule.

Complications

The syndrome is associated with an increased risk of breast cancer , pulmonary disease , varicose veins , and osteoporosis .

Calling your health care provider

Call for an appointment with your health care provider if a boy fails to develop secondary sexual characteristics. Genetic counseling is strongly recommended.