From the Department of Neurology and Mayo Clinic Center for Multiple Sclerosis and Autoimmune Neurology (L.C., J.J.C., S.B.S.-M., V.R., J.-M.T., S.J.P., E.P.F.), Mayo Clinic, Rochester, MN; Queen Square MS Centre (O.A.-M., D.C., C.H., O.C., Y.H.), UCL Queen Square Institute of Neurology, Faculty of Brain Sciences, University College London; Department of Neurology (O.A.-M., D.C., C.H., Y.H.), and Department of Neuroradiology (K.M.), Great Ormond Street Hospital for Children, London, United Kingdom; Department of Radiology (K.N.K.), Department of Ophthalmology (J.J.C.), and Laboratory Medicine and Pathology (S.J.P., E.P.F.), Mayo Clinic, Rochester, MN; Department of Neurology (A.S.L.-C.), Mayo Clinic, Jacksonville, FL; Department of Neurology (C.V.-S.), Mayo Clinic, Phoenix, AZ; and NIHR University College London Hospitals Biomedical Research Centre (O.C.), United Kingdom.