| Subject | Contents |
| Definition | 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. |
| Symptoms | small penis small firm testicles diminished pubic, axillary, and facial hair sexual dysfunction enlarged breast tissue (called gynecomastia ) tall stature abnormal body proportions (long legs, short trunk) learning disabilities personality impairment simian crease (a single crease in the palm) Note: the severity of symptoms may vary |
| 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: karyotyping showing 47 X-X-Y semen exam showing low sperm count decreased serum testosterone level increased serum luteinizing hormone increased serum follicle stimulating hormone |
| 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. |
| Prevention | |
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