The ketogenic diet will begin after the tests are completed. The diet provides mainly fats to fuel the body, plus the recommended amount of protein and minimum carbohydrate. Vitamin and mineral supplements are provided to meet daily requirements. After 2 weeks on the diet, the patient will be discharged from the hospital and seen daily as an outpatient for another 1 to 2 weeks. During this time the patient or caregiver is trained in preparing the ketogenic diet, and then the patient is discharged to home. Throughout the study, disease symptoms will be assessed using standardized rating scales. Blood and urine tests will be done as needed, as will follow-up brain imaging, neuropsychological and neurophysiological evaluations.