Efficacy, Safety, and Tolerability of Zeleciment Basivarsen (DYNE-101) in Participants With Myotonic Dystrophy Type 1

Inclusion Criteria: * Diagnosis of DM1 confirmed by molecular genetics with trinucleotide repeat size greater than (\>) 100. Historical results from clinical testing are acceptable. * Able to walk 10 meters and complete 5 times sit to stand independently (inserts or supports that don't go above the ankle are allowed). * Body mass index (BMI) less than (\<) 35 kilograms per meter square (kg/m\^2). Exclusion Criteria: * A known diagnosis of congenital DM1. * History of major surgical procedure (based on Investigator judgment) within 12 weeks prior to the start of screening, with the exception of implanted pacemaker or defibrillator. * Use of glucagon-like peptide 1 (GLP-1) agonist/incretin medications including semaglutide, dulaglutide, liraglutide, exenatide, or tirzepatide within a period of 5 half-lives of the medication prior to performing screening assessments. Note: Other inclusion and exclusion criteria may apply.