Lead Sponsor: Biogen

Intervention / Treatment: DRUG: BIIB132-Matching Placebo, DRUG: BIIB132

Lead Sponsor: The Methodist Hospital Research Institute

Collaborators: Hospital de Clinicas de Porto Alegre

Intervention / Treatment: OTHER: Non-interventional study

Lead Sponsor: The Methodist Hospital Research Institute

Collaborators: University of Pennsylvania, University of Rochester, Emory University, University of California, San Francisco, University of Minnesota, University of California, Los Angeles, Northwestern University, Stanford University, University of Alabama at Birmingham, University of Iowa, University of South Florida, University of Michigan, Columbia University, University of Utah, University of Chicago, University of Colorado, Denver, University of Florida, Johns Hopkins University, Ohio State University, Harvard University, German Center for Neurodegenerative Diseases (DZNE), Institut de Recherche sur la Moelle épinière et l'Encéphale