Department of Neurology (N.A.G., J.C., T.I., N.A., M.W., V.L., T.M., S.A.V.), MDA ALS and Neuromuscular Center (N.A.G., J.C., T.I., N.A., M.W., V.L., T.M.), Department of Pathology and Laboratory Medicine (T.M.), Department of Physiology and Biophysics (G.C., J.D., P.K.F., A.H.M., S.A.V.), Institute for Immunology (G.C., J.D., P.K.F., A.H.M., T.M., S.A.V.), and Biostatistics, Epidemiology, and Research Design (BERD) Unit, Institute for Clinical Translational Sciences (L.Z.), University of California, Irvine; Department of Neurology (J.C.), University of New Mexico, Albuquerque; Department of Neurology (L.W.), University of Washington Medical Center, Seattle; Department of Neurology, Division of Neuromuscular Disease (S.A.G.), Brigham and Women's Hospital and Harvard Medical School; and Computational Health Informatics Program (S.A.G.), Boston Children's Hospital and Harvard Medical School, MA.