XYY\xa0syndrome\xa0is a genetic condition that occurs when a male has an extra copy of the Y chromosome in each of their cells (XYY). Sometimes, this mutation is only present in some cells. Males with XYY\xa0syndrome\xa0have 47 chromosomes because of the extra Y chromosome.\xa0Most cases of 47,XYY\xa0syndrome\xa0are not\xa0inherited. The chromosomal change usually occurs as a random event during the formation of sperm cells. An error in cell division called nondisjunction can result in sperm cells with an extra copy of the Y\xa0chromosome.Boys with XYY syndrome may have some or all of these physical symptoms to some degree:\ttaller than average height.\tlow muscle tone, or muscle weakness (called hypotonia)\tvery curved pinky finger (called clinodactyly)\twidely spaced eyes (called hypertelorism)\tcystic acne during adolescence.