This longitudinal study will be conducted at Boston Children's Hospital (BCH). Subjects recruited for the study will have routine clinical care assessment with a complete physical and neurological exam and biochemical monitoring with venipuncture. In addition as part of the study, subjects will be given questionnaires to assess details of medical and psychosocial history, will complete self-reported measures of neuropsychological evaluation, pain scores, quality of life, executive functioning and cognitive functioning. All patients assessments will be repeated every 2 years.