Only 6.5% of first demyelinating event participants (9.2% of those with a first demyelinating event only at baseline interview) were on multiple sclerosis disease-modifying therapy (all interferon-beta) at the time of the baseline interview—all were diagnosed as clinically definite multiple sclerosis by the 2–3 year follow-up. This evidence concerns the gene IFNB1 and multiple sclerosis.