Once you are off study, you will have an end-of-study visit. At this visit, your complete medical history will be recorded. You will be asked about any drugs you have taken and are taking. You will have a physical exam, including measurement of vital signs. You will have a neurological exam. Blood (about 2 tablespoons) will be drawn for routine tests. Urine will be collected over a 24-hour period to test kidney function and for routine tests. You will have an MRI of the brain and spine.