Definition:
Klinefelter syndrome is the presence of an extra X chromosome in a male.
Alternative Names:
47 X-X-Y syndrome
Causes, incidence, and risk factors:
Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males normally have an X and a Y chromosome (written as XY). Klinefelter syndrome is one of a group of sex chromosome problems. It results in males who have at least one extra X chromosome. Usually, this occurs due to one extra X (written as XXY). Klinefelter syndrome is found in about 1 out of every 500 - 1,000 newborn males. Women who have pregnancies after age 35 are slightly more likely to have a boy with this syndrome than younger women.
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