2. Subjects may be male or female; age range: 6 - 17.5 years; weight ≥ 20 kg. They must be physically healthy and able to move about, with or without aids, must be living in the community, and must have adequate motor skills as shown by tests that will be given at the time of screening. The subject's eyesight and hearing must be good enough to allow cooperation with tests and physical examinations. Additionally, they must be able to swallow tablets.