What is Klinefelter syndrome? Klinefelter syndrome is a
Reference genetic disorder Opens New Window that affects males.
Klinefelter syndrome occurs when a boy is born with one or more
extra X Reference chromosomes Opens New Window. 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 XXY males or males with XXY 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 eggs splits unevenly. But it can also occur when the
genetic material in the sperm splits unevenly. 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 t