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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
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
See a picture of a
male with Klinefelter syndrome.
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.
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
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
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
Speech therapy and educational support
can help boys who have language or learning problems.
If your son has been
diagnosed with Klinefelter syndrome:
Learning about 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.
ByHealthwise StaffPrimary Medical ReviewerJohn Pope, MD - PediatricsMartin J. Gabica, MD - Family MedicineAdam Husney, MD - Family MedicineKathleen Romito, MD - Family MedicineSpecialist Medical ReviewerSiobhan M. Dolan, MD, MPH - Reproductive Genetics
Current as ofFebruary 23, 2018
Current as of:
February 23, 2018
John Pope, MD - Pediatrics
& Martin J. Gabica, MD - Family Medicine & Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics
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