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.