Skip to Content
Home > Health Information > 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 disorder, 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.
See a picture of a male with Klinefelter syndrome.
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 a chromosome test called a karyotype.
In adult men, lab tests in addition to a karyotype may be done, such as hormone tests or a semen analysis, if Klinefelter syndrome is suspected.
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:
Other Works Consulted
Achermann JC, Hughes IA (2011). Disorders of sex development. In S Melmed et al., eds., Williams Textbook of Endocrinology, 12th ed., pp. 868–934. Philadelphia: Saunders.
Bojesen A, et al. (2003). Prenatal and postnatal prevalence of Klinefelter syndrome: A national registry study. Journal of Clinical Endocrinology and Metabolism, 88(2): 622–626.
Braunstein GD (2011). Testes. In DG Gardner, D Shoback, eds., Greenspan's Basic and Clinical Endocrinology, 9th ed., pp. 395–422. New York: McGraw-Hill Medical.
Saenz M et al. (2014). Genetics and dysmorphology. In WW Hay Jr, et al., eds., Current Diagnosis and Treatment: Pediatrics, 22nd ed., pp. 1134–1170. New York: McGraw-Hill.
Current as of: April 1, 2019
Author: Healthwise StaffMedical Review: John Pope, MD, MPH - PediatricsMartin J. Gabica, MD - Family MedicineAdam Husney, MD - Family MedicineSiobhan M. Dolan, MD, MPH - Reproductive Genetics
Current as of:
April 1, 2019
Medical Review:John Pope, MD, MPH - 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.
© 1995-2019 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Our interactive Decision Points guide you through making key health decisions by combining medical information with your personal information.
You'll find Decision Points to help you answer questions about:
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.
Feeling under the weather?
Use our interactive symptom checker to evaluate your symptoms and determine appropriate action or treatment.
See important information from Billings Clinic on Non-discrimination and Interpreter Services.
Billings Clinic is proud to be an equal opportunity/affirmative action (EOE/AA) e-verify employer.