Facts About the Genetics of Klinefelter Syndrome: A Guide to the Cause, Signs and Symptoms of This Genetic Disorder

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The genetics of Klinefelter syndrome involve an extra X chromosome in males. This condition affects the sexual development of males. The testicles do not normally develop, resulting in low levels of the testosterone hormone when the patient reaches puberty. It is estimated that one in 500 to 1,000 males are affected by this condition. Females are not affected.

Genetics and Cause

In understanding the genetics of Klinefelter syndrome, we know that the extra X chromosome is present in male cells. Having these extra gene copies on the X chromosome causes interference with the sexual development in males. This is a genetic disorder, but not typically hereditary in the traditional sense, meaning it does not run in families and is not inherited. It stems from a random event during reproductive cell formation.

Signs and Symptoms

Males with this disorder are likely to have abnormal body proportions, such as a short trunk, long legs and equal hip and shoulder size. Their body hair (armpit, pubic and facial) is typically less than normal. Other signs and symptoms include abnormally large breasts, sexual problems, small and firm testicles, infertility and tall height.

Making the Diagnosis

In many cases, this disorder is not diagnosed until a male sees his doctor complaining of infertility. Also, infertility is the most common syndrome. Doctors may perform a semen count and karyotyping. Karyotyping is a type of test done to analyze chromosomes in a sample of cells. This can help doctors identify genetic problems and determine if they are the cause of disease or disorder.

Next, the doctor will often perform blood testing to look at hormone levels. The following blood tests may be performed: follicle stimulating hormone, testosterone, estradiol and luteinizing hormone.

Treating the Disorder

Testosterone therapy is generally prescribed to treat this disorder. This therapy is often beneficial in helping to grow body hair, improve concentration, increase sex drive and energy, improve muscle appearance, improve self-esteem and mood, and increase strength. Not all men require this therapy, but most will benefit from it. An infertility specialist may be able to help with infertility issues, though not all can be solved.

Possible Complications

In addition to the signs and symptoms above, men with this syndrome may also experience certain complications. They may have enlarged teeth with a thinning surface, known as taurodontism. This genetic disorder also increases a male’s risk of the following:

  • Lupus, Sjogren syndrome, rheumatoid arthritis and other autoimmune disorders
  • Depression
  • Extragonadal germ cell tumor
  • Osteoporosis
  • Attention deficit hyperactivity disorder
  • Breast cancer in men
  • Learning disabilities
  • Lung cancer
  • Varicose veins


Genetics Home Reference. (2008). Klinefelter Syndrome. Retrieved on March 29, 2011 from Genetics Home Reference: https://ghr.nlm.nih.gov/condition/klinefelter-syndrome

PubMed Health. (2010). Klinefelter Syndrome. Retrieved on March 29, 2011 from PubMed Health: https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001420/