Multicenter Observational Study of Myotonic Dystrophy Type 1

The purpose of the study is to determine the best ways to assess how people are affected by myotonic dystrophy type 1 (DM1). The study will assess walking speed, muscle strength, muscle size, myotonia, heart rhythm, mental efficiency, and overall health. Participants will complete questionnaires to record their ideas about how they are affected by DM1. The study will evaluate people with DM1 over 1 year to determine how the condition changes over time. The study will identify biomarkers of DM1. Biomarkers are laboratory measurements that show the effects of DM1 on a person's muscle tissue or blood. Biomarkers are needed in future studies to determine how DM1 may respond to treatments.