1 Department of Neurology, Keck School of Medicine, University of Southern California (USC), Los Angeles, CA, USA.
2 Department of Neurology, University of Pennsylvania, Philadelphia, PA, USA.
3 Queen Square Multiple Sclerosis Centre, UCL Queen Square Institute of Neurology, Faculty of Brain Sciences, University College London (UCL), London, UK; NIHR University College London Hospitals Biomedical Research Centre, London, UK.