ABSTRACT Objective In multiple sclerosis, the optimal time for deploying a therapeutic intervention is before the central nervous system is damaged; given the success of trials treating the earliest stage of MS, the radiologically isolated syndrome, developing primary prevention strategies is an important next challenge. To inform this question, we examined the conversion of asymptomatic family members to a diagnosis of MS among Genes and Environment in Multiple Sclerosis (GEMS) project participants. We also evaluated an updated Genetic and Environmental risk score (GERS) and interest in participation in primary prevention trials. Methods GEMS is a nationwide prospective study of first‐degree relatives of persons with MS; we analyzed data from seven surveys completed over 11 years. 1903 participants completed all questionnaires at study entry. Biological samples were collected in a subset of participants. Results Among these 1903 first degree relatives, 141 participants had MS at the time of enrollment; 18 participants converted to MS; and 1744 participants did not acquire an MS diagnosis during 8526 person‐years of observation. The GERS was significantly higher among participants who had MS at the initial survey than those who did not have an MS diagnosis. The incidence rate of MS was estimated as 211 cases with a 95% confidence interval of 113 to 308 cases per 100,000 first‐degree family members per year, which is 100 times greater than the reported incidence of sporadic MS. 48% of the asymptomatic participants were willing to participate in a prevention trial, while 75% expressed willingness when presented with a scenario assuming an elevated risk (20%) of developing MS based on genetic tests performed with blood samples. Interpretation Primary prevention trials in MS are urgently needed. Our findings support the feasibility for such studies and inform the design of future primary prevention trials in individuals at risk for MS. Trial Registration ClinicalTrials.gov identifier: NCT01353547
Laitinen et al. (Tue,) studied this question.