XX male syndrome (also called de la Chapelle syndrome) is a rare sex chromosomal disorder in men. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis. Symptoms include small testes, gynecomastia and sterility.

Men typically have one X chromosome and one Y chromosome in each cell of their bodies, other than sperm cells. Women typically have two X chromosomes. XX males have two X chromosomes, but otherwise appear to be male.

There are a number of other syndromes related to the karyotype of the sex chromosomes, such as XYY syndrome, Turner syndrome (patients have one X and no Y chromsome), Klinefelter syndrome (patients have two X chromosomes and one Y), XXX syndrome (patients have three X chromosomes), etc. See the list of genetic disorders.

In the media

• The main character of the Japanese manga The Day of Revolution, Kei Yoshikawa, has XX male syndrome.

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Diseases