Additional Study Information: This study is being done to find out whether drug that is used for relapsing forms of multiple sclerosis (MS) called Tecfidera (dimethyl fumarate) can delay the onset of MS symptoms in people with radiographically isolated syndrome. Half the participants enrolled in this study will receive the medication and half will receive a placebo (no active ingredient). Neither participants or the study team will choose or even know which treatment they are getting.