First Time User? Enroll now.
As the COVID-19 situation has evolved, our visitor policy is evolving as well. Get full details.
For the most current information, please visit our Coronavirus resource pages.
Home > Health Library > Klinefelter Syndrome
Klinefelter syndrome is a genetic condition that affects males. Klinefelter syndrome occurs when a boy is born with one or more extra X chromosomes. Most males have one Y and one X chromosome. Having extra X chromosomes can cause a male to have a variety of physical traits.
Many men with an extra X chromosome are not aware that they have it, and they lead normal lives. Klinefelter syndrome occurs in about 1 out of 1,000 males.
The presence of an extra X chromosome in males most often occurs when the genetic material in the egg splits unevenly. But it can also occur when the genetic material in the sperm splits unevenly. Even though Klinefelter syndrome is a genetic condition, it is not passed down through families. So, parents who have a child with Klinefelter syndrome are not any more likely than other couples to have another child with the condition.
Many men who have Klinefelter syndrome do not have obvious symptoms. Others have sparse body hair, enlarged breasts, and wide hips. In almost all men the testicles remain small. In some men the penis does not reach adult size. Their voices may not be as deep. They usually have infertility. But they can have a normal sex life.
Some boys with Klinefelter syndrome have language and learning problems.
Klinefelter syndrome usually is not diagnosed until the time of puberty. At this point, the boy's testicles fail to grow, and you may start to notice other symptoms.
To find out if your son has Klinefelter syndrome, your doctor will ask questions about his past health, do a physical exam, and order tests, such as a hormone test and chromosome analysis.
In adult men, other tests may be done, such as semen analysis.
Sometimes Klinefelter syndrome is found before a baby is born (prenatally). Genetic tests on cells collected from amniocentesis or chorionic villus sampling (CVS) can show when a baby boy has Klinefelter syndrome. So the condition may be found when a pregnant woman has genetic tests for another reason.
Males with Klinefelter syndrome can be given testosterone, a hormone needed for sexual development. If treatment is started around the age of puberty, it can help boys with the sexual development of their bodies.
Testosterone is given by injection or through a skin patch or gel. The treatment usually continues throughout a man's life but does not help infertility.
Speech therapy and educational support can help boys who have language or learning problems.
If your son has been diagnosed with Klinefelter syndrome:
Current as of:
March 3, 2021
Author: Healthwise StaffMedical Review: John Pope MD - PediatricsMartin J. Gabica MD - Family MedicineAdam Husney MD - Family MedicineSiobhan M. Dolan MD, MPH - Reproductive Genetics
Current as of: March 3, 2021
Author: Healthwise Staff
Medical Review:John Pope MD - Pediatrics & Martin J. Gabica MD - Family Medicine & Adam Husney MD - Family Medicine & Siobhan M. Dolan MD, MPH - Reproductive Genetics
To learn more about Healthwise, visit Healthwise.org.
© 1995-2021 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Feeling under the weather?
Use our interactive symptom checker to evaluate your symptoms and determine appropriate action or treatment.
Get started learning more about your health!
Our Interactive Tools can help you make smart decisions for a healthier life. You'll find personal calculators and tools for health and fitness, lifestyle checkups, and pregnancy.