Study to Evaluate Oral BIIB061 Added to Interferon-beta1 (IFN-β1) or Glatiramer Acetate in Relapsing Multiple Sclerosis (RMS)

The primary objectives of the study are to evaluate the safety of BIIB061 versus placebo in participants with Relapsing Multiple Sclerosis (RMS), and to evaluate the efficacy of BIIB061 to improve disability outcome versus placebo in participants with RMS. The secondary objectives of the study are to evaluate the effects of BIIB061 versus placebo on brain magnetic resonance imaging (MRI) markers of remyelination and axon preservation in chronic Multiple Sclerosis lesions and to evaluate the effects of BIIB061 versus placebo on additional measures of improved disability outcome.