47 X-X-Y syndrome

Alternative names 
Klinefelter syndrome

Klinefelter syndrome is a chromosome abnormality that affects only men and causes hypogonadism.

Causes, incidence, and risk factors

A person’s sex is determined by the X and Y chromosomes. Normally, men have an X and a Y and women have two X’s. In Klinefelter syndrome, a male has two X’s and a Y.

The condition is common and affects 1 in 500 men. The infant appears normal at birth, but the defect usually becomes apparent in puberty when secondary sexual characteristics fail to develop (or develop late). At this time, 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.

One risk factor for this condition is the mother giving birth at an older age. In most cases, the problem develops during fetal development and is not inherited from one or both parents.


  • 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

Note: the severity of symptoms may vary

Signs and tests
During a physical examination, the doctor will look for a simian crease (a single crease in the palm). A 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  
  • increased serum estradiol levels (a type of estrogen)


There is no treatment for the infertility associated with this syndrome. Testosterone therapy will improve the development of secondary sexual characteristics. Testosterone treatment usually starts at the beginning of puberty. Once this treatment begins, it needs to be continued for life. The testicular changes that lead to infertility are not preventable.

Enlarged breast tissue (Gynecomastia) can be treated with plastic surgery if it is disfiguring.

Counseling may benefit people with emotional difficulties due to sexual dysfunction and to reinforce male identity.

Support Groups

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

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


The syndrome is associated with an increased risk of breast cancer, extragonadal germ cell tumor (a rare tumor), pulmonary 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, despite normal or high IQ are common. The risk of dyslexia and attention deficient hyperactivity disorder may also be higher. Psychological problems like depression are associated with sex-linked disorders.

Taurodontism, an enlargement of the pulp of the teeth with surface thinning, is very common in Klinefelter syndrome. It can be diagnosed by dental x-rays.

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

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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