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What causes Klinefelter syndrome?

Klinefelter syndrome is typically caused by what is called nondisjunction, more specifically nondisjunction of the sex chromosomes. The X and Y chromosome are known as sex chromosomes, and their presence or absence determines the gender of the embryo. Normally, males inherit one X chromosome from their mother and one Y chromosome from their father. But those who have Klinefelter syndrome inherit an extra X chromosome.

The presence of an extra X chromosome is the result of a pair of sex chromosomes that fail to separate during the formation of the gamete (ova or sperm) in the parent.  This failure to separate is referred to as nondisjunction. When the gamete with the extra chromosome unites with a normal gamate to form an embryo, that embryo may end up with three copies of the sex chromosomes (XXY) instead of the normal two (XY). The extra chromosome is then copied in every cell of the baby's body.

The cause of Klinefelter syndrome is an extra copy of the X chromosome. Males with this condition have two X chromosomes and one Y chromosome.  Klinefelter syndrome is caused by a random mistake in chromosome development and recurrence risk is low if someone in your family is affected.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.