Klinefelter syndrome

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at June 17, 2016
StartDiseasesKlinefelter syndrome

Klinefelter syndrome, affecting only males, is a chromosomal condition that alters a child's physical and cognitive development. People who have Klinefelter syndrome are born with at least one additional X chromosome. Symptoms for this condition vary greatly from person to person.


Definition & Facts

Klinefelter syndrome was initially identified in 1942 by an American physician named Harry Fitch Klinefelter at the Massachusetts General Hospital. Boys who are born with this syndrome do not have any signs or symptoms at birth. While most enter puberty without symptoms, their levels of testosterone may be noticeably low by mid-puberty. This can result in small testicles and an inability to create sperm.

People suffering from Klinefelter syndrome may also have behavioral problems and learning disabilities. This syndrome is among the most common chromosomal abnormalities. Approximately 0.2-0.12% of males are born with Klinefelter syndrome, which is about 3,000 boys each year in the United States. 3% of male infertility is due to Klinefelter syndrome, which equally affects all races.

Symptoms & Complaints

Symptoms vary by patient; oftentimes, boys who have Klinefelter syndrome do not have noticeable symptoms. This may leave the condition undiagnosed until adulthood. Some boys, however, experience an immense negative effect on their growth and appearance as well as learning disabilities and speech problems.

For babies, some common symptoms include slow motor development, weak muscles, quiet personality, and speech delay. In older children and teenagers, it is common to be tall with long legs and a short torso, small penis and small testicles, incomplete puberty, less muscular body, enlarged breasts, weak bones, shyness, low energy levels, difficulty socializing, attention problems, and problems in school. In addition to the above symptoms, men may experience decreased facial hair and low sex drive.

Most men who have Klinefelter syndrome are infertile and therefore unable to have children, due to the fact that the testicles do not produce sperm. While some men with this syndrome have a possibility of having minimal sperm production, it is not common.


Klinefelter syndrome is due to a random error that leads to a male being born with an additional sex chromosome. While females have XX chromosomes and males have XY chromosomes, people born with Klinefelter have an extra X chromosome, making their chromosomes XXY. The extra copy of the X chromosome interferes with male fertility and sexual development.

While Klinefelter syndrome is a genetic disorder as well as a congenital disorder, it is not an inherited condition. The cause of Klinefelter syndrome is due to random errors during the formation of the zygote.

Diagnosis & Tests

In order to reach a diagnosis and recommend a course of treatment for Klinefelter syndrome, a doctor will likely physically examine the genital area and chest to check for abnormalities. In addition, the doctor may perform tests that evaluate cognitive function and reflexes as well as test for abnormal levels of hormones through a blood test or a urine sample.

Another option for testing is karyotyping or chromosome analysis. This also requires drawing a blood sample, and it is used to evaluate the shape and number of chromosomes. A karyotype test can confirm that an additional chromosome is present. This test can be done at any point in one's life and it will show the same results. These tests can be done prior to birth with an amniocentesis, but this is not typically done unless the family has a history of chromosomal disorders.

Treatment & Therapy

While there is no cure for Klinefelter syndrome, there are treatments available that can help minimize the negative effects. A patient who is diagnosed with Klinefelter syndrome should seek early treatment; the sooner a diagnosis is made and treatment has begun, the greater the potential for the individual with Klinefelter syndrome to have a higher quality of life. Working with a team of health care professionals can be beneficial, including an endocrinologist, a pediatrician, a speech therapist, a physical therapist, a reproductive medicine specialist, a genetic counselor, and a psychologist.

One treatment for Klinefelter syndrome is testosterone replacement therapy. This form of hormone replacement therapy addresses the underproduction of testosterone caused by Klinefelter syndrome and its attendant effects. Testosterone replacement therapy can be administered via injection or topically with a gel or patch.

Boys are able to undergo the normal body changes that come along with puberty with testosterone replacement therapy. These changes include developing a deeper voice, increasing muscle mass, growing facial hair, growing penis size, and growing body hair. Testosterone replacement therapy is also able to improve bone density, which in turn reduces the risk of bone fractures. However, this will not help a man become more fertile, nor will it increase the size of the testicles. Some studies have shown that testosterone replacement therapy increases the risk of male infertility.

Breast tissue removal is often done in men who develop gynecomastia, which will leave a man with a more masculine-looking chest. Speech therapy and physical therapy are able to help boys overcome problems with their speech and muscle weakness.

Prevention & Prophylaxis

Due to the fact that Klinefelter syndrome is caused by a random genetic mutation, there is currently no known way to prevent the syndrome from happening. As a mother ages, the risk of her child being born with Klinefelter syndrome increases. While choosing to have children under the age of 35 does not guarantee prevention, it reduces the risk. Women who are over the age of 35 are encouraged to speak to their OBGYN prior to getting pregnant to talk about the possibilities of Klinefelter syndrome.

People who think they may be suffering from Klinefelter syndrome are urged to see their doctor immediately, as early intervention with the right care and support makes a big difference in the individual's quality of life in the long run.