Most men are born with a pair of xy chromosomes, while most females are born with pair of xx chromosomes. Klinefelter syndrome occurs when a male is born with an extra x chromosome. Xxy occurs when a male has an extra x chromosome in some or all cells of his body.

Klinefelter syndrome, also called 47,xxy, is a chromosomal condition that affects male development. The signs and symptoms of klinefelter syndrome vary. In some cases, the features are so mild that … Those with xxy are more likely than others to have certain health problems, such as autoimmune disorders, breast cancer, venous thromboembolic disease, and osteoporosis.