From the Ann Romney Center for Neurologic Diseases (K.R., A.P., B.H., F.v.G., M.A.M., R.R., P.K., T.C., H.L.W., R.G.), and Partners MS Center (C.D.-C., T.G., P.N., B.I.G., T.C., H.L.W.), Brigham & Women's Hospital, Harvard Medical School, Boston; and Biostatistics Center (B.H.), Massachusetts General Hospital, Boston. (At 2016-10)