XX male syndrome (also called de la Chapelle syndrome) is a rare sex chromosomal disorder in man. 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 chromosome), Klinefelter syndrome (patients have two X chromosomes and one Y), XXX syndrome (patients have three X chromosomes), etc.