True giants have an abnormal growth on their pituitary gland (I think, it's been a while) that causes them to grow to such massive size. Unfortunately that growth also prevents them from ever adding much muscle mass and contributes to a host of other health problems. If memory serves they are also subject to enlarged heart, heart failure, pvd, and other serious issues. The giant you refer to has undergone surgery to try and have the growth removed with the hope of then adding enough muscle to become a viable NBA player.
