Klinefelter Syndrome FAQs

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Providence, RI 02906

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What is Klinefelter syndrome?

Klinefelter syndrome is one of the most common genetic disorders affecting one-in-500 to one-in-one-thousand live male births. It affects both physical and intellectual development, and signs and symptoms vary among affected individuals. Common signs and symptoms include small testes, low testosterone levels, decreased muscle mass, enlarged breast tissue (gynecomastia) and reduced facial and body hair.

Older children and adults with Klinefelter syndrome tend to be somewhat taller than their peers and may have characteristic changes in their hands and feet. Physical changes can be subtle, and many men do not discover that they have Klinefelter syndrome until later in adulthood.

What causes it?

The condition is caused extra genetic material that affects the development of the testicles. The change occurs by random error and is not passed from parents to children. Of a human’s 46 chromosomes, two sex chromosomes determine a person’s sex: females have two X chromosomes and males have an X and a Y chromosome.

The most common cause of Klinefelter syndrome is an extra copy of the X chromosome (or part of an X chromosome) in each cell. Since it is a random genetic event, there is nothing a parent did or didn’t do to cause it. The only known risk factor is the advanced age of the mother during pregnancy, and even then, the risk is only slightly higher.

How do I get tested?

Your doctor will perform a thorough history and physical exam and ask detailed questions about symptoms and health. The main tests to determine Klinefelter syndrome are hormone testing and chromosome analysis. Hormone tests are blood tests that can reveal abnormal hormone levels and signs of the syndrome. During a chromosome analysis, a blood sample is sent to a lab to confirm the number and characteristics of chromosomes.

What treatment options are available?

Usually, the earlier you start treatment, the more effective it will be. Testosterone replacement therapy is the most common treatment and typically begins at the onset of puberty. It is given to help stimulate changes that would normally occur during this time, such as a deeper voice, facial and body hair, and increasing body mass and penis size. Other treatments include counseling, fertility treatment, plastic surgery to reduce breast size, occupational and physical therapy to help with muscle mass, and educational evaluation and support.

Although there's no way to repair the sex chromosome changes due to Klinefelter syndrome, treatments can help minimize its effects. The earlier a diagnosis is made and treatment is started, the greater the benefits. 

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