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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 may be present in an individual that has two X chromosomes and one Y chromosome (47, XXY); usually, males have one X and one Y (XY) and females have two X chromosomes (XX). Some individuals with a 47, XXY chromosome finding may have no obvious signs or symptoms of KS while others may have several features and varying degrees of cognitive, social, behavioral, and learning difficulties.[1] Because features may not be apparent until mid to late adolescence, the term “Klinefelter syndrome” is often reserved for affected adolescents and adults. Although the vast majority of boys with KS identify as males, some individuals develop atypical gender identities.[2] In adulthood, individuals with Klinefelter syndrome may have primary hypogonadism (decreased testosterone production), small testes, enlarged breast tissue (gynecomastia), tall stature, and/or other features.[1] The vast majority of males with KS are infertile, but many produce sperm and may be able to conceive with assisted reproduction. Treatment varies among individuals and may include testosterone therapy; however, this therapy may not be appropriate for all individuals.[2]
Last updated: 9/20/2013

What are the signs and symptoms of Klinefelter syndrome?

Because XXY males do not really appear different from other males and because they may not have any or mild symptoms, XXY males often don't know they have Klinefelter syndrome (KS).   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.[3]   Symptoms may include:

  • Abnormal body proportions (long legs, short trunk, narrower shoulders and wider hips)
  • Breast growth (gynecomastia)
  • Infertility: Nearly all men with KS are unable to father a biologically-related child without help from a fertility specialist.
  • Decreased sexual interest
  • Less than normal amount of pubic, armpit, and facial hair
  • Small, firm testicles
  • Tall height

Boys with Klinefelter syndrome may also have learning disabilities and difficulty with speech and language development. They tend to be quiet, sensitive, and unassertive, but personality characteristics vary among males with this condition. [4]

Last updated: 3/3/2010

What causes Klinefelter syndrome?

Klinefelter syndrome is not inherited; it 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.[5]

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 chromsomes (46, XX). Individuals with Klinefelter syndrome usually have two X chromosomes and one Y chromosome (47, XXY). Some individuals with Klinefelter syndrome have the extra X chromosome in only some of their cells; these individuals are said to have mosaic Klinefelter syndrome.[5]

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.[6]

The features of Klinefelter syndrome are due to the extra copies of genes on the extra X chromosome, which can alter male sexual development.[4]
Last updated: 9/18/2013

How might Klinefelter syndrome be treated?

Because symptoms of Klinefelter syndrome (KS) can sometimes be very mild, many individuals are never diagnosed or treated. The type of therapies available for individuals seeking treatment depends on the type of symptoms present. There are conflicting opinions in some of the literature about when treatment should be started and who should be treated. The earlier in life that KS symptoms are recognized and treated (for example, by early puberty), the more likely it is that the symptoms can be reduced or eliminated. However, although the majority of boys with KS grow up to live as males, some reportedly develop atypical gender identities. For these individuals, certain therapies (such as supplemental testosterone) may not be suitable. Gender identity should be discussed with health care providers before starting treatment.[7]

Management options available to individuals with signs and symptoms of Klinefelter syndrome may include:
  • Educational interventions – As children, many individuals 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 individuals with KS have low testosterone levels, which may be raised by taking supplemental testosterone. Having a more normal testosterone level can help individuals 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, and this therapy also may not be suitable for some individuals depending on gender identity.[8][7] Some individuals may opt to have breast removal or reduction surgery.[7]
Last updated: 9/20/2013

What is the prognosis for individuals 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.  [9]

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. [9]

Advocacy organizations can be a helpful source of additional information and support for individuals, friends and family members with Klinefelter syndrome.  A list of advocacy organizations for Klinefelter syndrome can be found under the GARD's Support Group tab.

Last updated: 6/30/2011

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 6/5/2014

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.