This study looks at the safety of a drug called PGN-EDODM1 for people with Myotonic Dystrophy Type 1 (DM1), a genetic disorder that causes muscle problems. Participants will get a single dose through an IV (a tube into a vein). The study lasts about 4 months, with two parts: a Screening Period (up to 30 days) to check if you can join, and a Treatment and Observation Period (16 weeks) to monitor the effects.

To join, you need a confirmed DM1 diagnosis and should be able to move certain muscles well. You can't join if you have a type of DM1 present at birth, other major health issues, or if you're taking certain medicines.

• The study takes about 4 months in total.
• Participants will get one IV dose and be monitored.
• Certain health conditions or medications may disqualify you from joining.