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Klinefelter Syndrome
Monday, 04 August 2003
Wednesday, 06 July 2005
47, XXY; 48, XXXY; 48, XXYY; 49, XXXXY


Klinefelter syndrome is a genetic disorder that was first described in 1942 and is caused by an abnormality of the number of sex chromosomes in males. Boys usually have 46 chromosomes (or 23 pairs), which includes the sex chromosomes X and Y. In Klinefelter syndrome, there is an extra X chromosome for a total of 47 chromosomes. This genetic makeup or “genotype” is represented in the medical literature as 47,XXY. Some individuals may have more than one extra sex chromosome. Having an extra X chromosome can lead to tall stature, low testosterone levels, and infertility.


Klinefelter syndrome affects boys and occurs in about 1 in 1,000 male births. It occurs in all ethnic groups.

Signs and Symptoms

Klinefelter syndrome is present from birth but boys usually appear normal in infancy and childhood. They may grow taller than other children their age which is usually due to long legs. After puberty, they may be noted to have small sized testes (hypogonadism). Some adolescent boys will show signs of breast development (gynecomastia). As adults, males are often infertile and have decreased libido. It is common for the diagnosis of Klinefelter syndrome to be found only after he has had difficulty having children. Only one fifth of affected men are able to grow a normal beard. They can develop osteoporosis and muscle weakness because they have decreased testosterone levels. There is a risk of obesity and diabetes. Intelligence is usually normal, but there is a risk for learning disabilities. Their areas of most difficulty include language skills, forming concepts, problem solving, and planning. Individuals with more than one extra X chromosome have more problems with intelligence and are not as tall.

Possible Causes

Klinefelter syndrome occurs because the boy inherits an extra sex chromosome from one of his parents. This phenomenon is called “nondysjunction” where the chromosomes do not separate normally and result in too many sex chromosomes in the fetus. The extra X chromosome can come from either parent. In about half of cases, it is inherited from the father (sperm), and half inherited from the mother (egg).


If a male is suspected to have Klinefelter syndrome because of the above symptoms, a special genetic test called a karyotype can confirm the diagnosis. This is a blood test to look at the number of chromosomes he has. This test can also be done during pregnancy on a sample of amniotic fluid (amniocentesis) to check if the fetus is affected.


There is no cure for Klinefelter syndrome. If the child has learning disabilities, he should receive additional help through educational programs at school and at home. Struggles with academics and self image can lead to emotional and behavioral problems which may be addressed with a psychologist or counselor. If an individual has low testosterone levels, treatment with testosterone is helpful. Replacing testosterone will help with a greater overall sense of well-being. With treatment, their mood, self-esteem, and behavior are better. They are less tired and irritable. Male characteristics such as body hair, strength, masculinity, and libido are improved. Testosterone is also important to prevent osteoporosis and heart disease. If breast development (gynecomastia) is bothersome, surgical removal (mastectomy) may be performed. Artificial reproductive techniques can help infertile men have children.


The prognosis for individuals with Klinefelter syndrome is good. Life expectancy is normal, unless they develop complications from obesity or diabetes. Most affected individuals mature and achieve full independence during adulthood.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


Klinefelter Syndrome
A website with clearly written explanations of Klinefelter Syndrome. There are also special articles dedicated to parents and teens as well as links to other resources.

American Association for Klinefelter Syndrome Information and Support
A website which provides support for families affected by Klinefelter Syndrome. There is also a guide for families on understanding this syndrome in both English and Spanish.

National Institute of Child Health and Human Development
A website with excellent information on the diagnosis and management of Klinefelter syndrome including what to tell family and friends.

Google Search for Klinefelter Syndrome

References and Sources

Lanfranco F, Kamischke A, Zitzmann M, Nieschlag E. Klinefelter's syndrome. Lancet. 2004 Jul 17;364(9430):273-83.