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What causes Klinefelter syndrome?

The extra chromosome results from a random error that occurs when a sperm or egg is formed; this error causes an extra X cell to be included each time the cell divides to form new cells. In very rare cases, more than one extra X or an extra Y is included.

« Condition Information How many people are affected/at risk? »

Last Updated Date: 11/30/2012
Last Reviewed Date: 11/30/2012