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Klinefelter syndrome is a 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. Klinefelter syndrome occurs in about 1 out of 1,000 males.
Klinefelter syndrome is a group of conditions that affects the health of males who are born with at least one extra X chromosome. Chromosomes, found in all body cells, contain genes. Genes provide specific instructions for body characteristics and functions. For example, some genes determine height and hair color.