During a 4-week screening period, eye movement velocity will be measured. These assessments will be repeated at months 12 and 24. Also at screening and months 12 and 24, the following tests will be done: MRI/CT, to measure spleen and liver volume; pulmonary imaging (by X-ray) and function tests; nerve conduction velocity studies and neuropsychological assessments; evoked response studies (to measure how the brain conducts electrical messages); and tremor measurements. Additional assessments for tremor will be conducted at months 6 and 18.