The purpose of this study is to evaluate the safety and effectiveness (how well a drug works) of Carbidopa/levodopa (Sinemet) in individuals with Angelman syndrome. Sinemet is a medication that helps to raise dopamine levels (a chemical that signals nerve cells) in the brain and central nervous system. There is evidence that dopamine concentrations may be abnormal in patients with Angelman syndrome. This study is investigating whether Sinemet helps motor control, intellectual function and the achievement of developmental milestones in people with Angelman syndrome