Klinefelter syndrome

Alternative names

47 X-X-Y syndrome

Definition

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.

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
  

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)
  

Treatment

There is no treatment for the 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 are not preventable.