Gagnon C, Mathieu J, Jean S, Laberge L, Perron M, Veillette S, Richer L, Noreau L. Predictors of disrupted social participation in myotonic dystrophy type 1. Objective To identify personal and environmental predictors of the most disrupted participation domains in people with myotonic dystrophy type 1 (DM1). Design Cross-sectional study. Setting Outpatient neuromuscular clinic. Participants Adults (n=200; 121 women), age 18 years or older (mean age, 47y), with a confirmed diagnosis of DM1 were selected from the registry of a neuromuscular clinic (N=416). Fifty-two participants had the mild phenotype and 148 the adult phenotype. Interventions Not applicable. Main Outcome Measures Social participation in mobility, housing, employment, and recreation was assessed with the Life Habits Measure. Disrupted participation was based on whether help was needed in performing most life habits because of incapacities or environmental barriers. Environmental factors were assessed by using the Measure of the Quality of the Environment. Personal factors were assessed with standardized instruments including the Berg Balance Scale, the Krupp Fatigue Severity Scale, and manual muscle testing. Results A large proportion of participants (45%–61%) reported disrupted participation in all 4 domains. Lower-extremity strength (odd ratios [OR], 15.0–5.5; P<.050) and higher fatigue (OR, 6.0–2.6; P<.05) were present in participants with disrupted participation. With regard to environmental factors, family support (OR, 3.6–2.5; P<.05) and public services (OR, 2.8–2.2; P<.05) were perceived as barriers for participants with disrupted participation in most domains. Conclusions This study identified personal and environmental factors that may influence the trajectory toward disrupted participation in individuals with DM1. Fatigue, strength, family support, and public services were found to be independent predictors of disrupted participation.