1 Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
2 Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, PA 19010, USA. Electronic address: banwellb@chop.edu.