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Diseases

Genetic and Rare Diseases Information Center (GARD)

Klinefelter syndrome


Other Names for this Disease
  • Klinefelter's syndrome
  • XXY syndrome
Related Diseases
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

We have just been told that our 2.5 year old grandson has Klinefelter syndrome.  We know very little about this condition and how it will affect him and his family in the future.  Where can we find additional information?  How can we find a health professional to discuss this in more detail?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is Klinefelter syndrome?

Klinefelter syndrome (KS) is a condition that occurs in males when they have an extra X chromosome. Some males with KS have no obvious signs or symptoms while others may have varying degrees of cognitive, social, behavioral, and learning difficulties. Adults with Klinefelter syndrome may also experience primary hypogonadism (decreased testosterone production), small testes, enlarged breast tissue (gynecomastia), tall stature, and/or infertility. KS is not inherited, but usually occurs as a random event during the formation of reproductive cells (eggs and sperm). Treatment is based on the signs and symptoms present in each person.[1][2][3]
Last updated: 10/13/2015

What are the signs and symptoms of Klinefelter syndrome?

The signs and symptoms of Klinefelter syndrome (KS) vary among affected people. Some men with KS have no symptoms of the condition or are only mildy affected. In these cases, they may not even know that they are affected by KS. When present, symptoms may include:[2][3][1]
  • Small, firm testicles
  • Delayed or incomplete puberty
  • Breast growth (gynecomastia)
  • Reduced facial and body hair
  • Infertility
  • Tall height
  • Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
  • Learning disablity
  • Speech delay

Whether or not a male with KS has visible symptoms depends on many factors, including how much testosterone his body makes, if he is mosaic (with both XY and XXY cells), and his age when the condition is diagnosed and treated.[1]
Last updated: 10/12/2015

What causes Klinefelter syndrome?

Klinefelter syndrome usually occurs as a random event during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain one or more extra copies of the X chromosome as a result of nondisjunction. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have one or more extra X chromosomes in each of the body's cells.[2]

Most often, Klinefelter syndrome is caused by a single extra copy of the X chromosome, resulting in a total of 47 chromosomes per cell. Males normally have one X chromosome and one Y chromosome in each cell (46, XY), while females have two X chromosomes (46, XX). People with Klinefelter syndrome usually have two X chromosomes and one Y chromosome (47, XXY). Some people with Klinefelter syndrome have the extra X chromosome in only some of their cells; these people are said to have mosaic Klinefelter syndrome.[2]

It is estimated that about half of the time, the cell division error occurs during development of the sperm, while the remainder are due to errors in egg development. Women who have pregnancies after age 35 have a slightly increased chance of having offspring with this syndrome.[4]

The features of Klinefelter syndrome are due to the extra copies of genes on the extra X chromosome, which can alter male sexual development.[3]
Last updated: 10/12/2015

How might Klinefelter syndrome be treated?

Because symptoms of Klinefelter syndrome (KS) can sometimes be very mild, many people are never diagnosed or treated. When a diagnosis is made, treatment is based on the signs and symptoms present in each person. This may include:[1][3][5]
  • Educational interventions - As children, many people with Klinefelter syndrome qualify for special services to help them in school. Teachers can also help by using certain methods in the classroom, such as breaking bigger tasks into small steps.
  • Therapeutic options - A variety of therapists, such as physical, speech, occupational, behavioral, mental health, and family therapists can often help reduce or eliminate some of the symptoms of Klinefelter syndrome such as poor muscle tone; speech and language problems; or low self-confidence.
  • Medical management - About half of people with KS have low testosterone levels, which may be raised by taking supplemental testosterone. Having a more normal testosterone level can help affected people develop bigger muscles, a deeper voice, and facial and body hair. Many healthcare providers recommend testosterone therapy when a boy reaches puberty. However, not all males with KS benefit from testosterone therapy. Some affected people may opt to have breast removal or reduction surgery.

The Eunice Kennedy Shriver National Institute of Child Health and Human Development's Web site offers more specific information on the treatment and management of Klinefelter syndrome. Please click on the link to access this resource.
Last updated: 10/13/2015

What is the long-term outlook for people with Klinefelter syndrome?

Babies with the 47, XXY form of Klinefelter differ little from healthy children. The results of one study on non-mosaic XXY infants younger than 2 years indicated that most XXY babies had normal external genitalia and facial features with height and weight in the normal range. Genetic testing had been performed due to a delay in walking and/or speech. Early detection of Klinefelter syndrome is shown to be important to monitor potential developmental problems.[5]

Boys with the 47, XXY karyotype may struggle through adolescence with academics, various frustrations, and, in a few instances, serious emotional or behavioral difficulties. However, most move toward full independence from their families as they enter adulthood. Some have completed graduate education and have a normal level of functioning.  Lifespan is not affected by Klinefelter syndrome.[5]
Last updated: 10/13/2015

How can I find a genetics professional in my area?

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by GeneTests, the American College of Medical Genetics, and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.
Last updated: 7/15/2016

References
Other Names for this Disease
  • Klinefelter's syndrome
  • XXY syndrome
Related Diseases
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.