This study will determine the rate of sugar metabolism in the brain of patients with Fabry disease, a genetic disease of abnormal lipid metabolism. Compared with healthy people, patients with Fabry disease have increased blood flow to the brain, which may result from abnormal brain metabolic activity. This study will use positron emission tomography (PET) and magnetic resonance imaging (MRI) to compare brain sugar metabolism in eight untreated patients, eight patients who are receiving enzyme replacement therapy, and eight healthy volunteers.