What is Klinefelter syndrome?
genetic disorder 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 some physical
traits unusual for males.
Many men with an extra X chromosome are
not aware that they have it, and they lead normal lives. Males who have Klinefelter
syndrome may be described as X-Y males or males with X-Y syndrome. Klinefelter
syndrome occurs in about 1 out of 1,000 males.
What causes Klinefelter syndrome?
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.
What are the symptoms?
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 cannot father children. 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 .
How is Klinefelter syndrome diagnosed?
syndrome usually is not diagnosed until the time of
puberty. At this point, the boy's testicles fail to
grow normally 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
Klinefelter syndrome can be detected before birth (prenatally) through
genetic tests on cells collected from amniocentesis or
chorionic villus sampling (CVS). But this is not
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