**Study Summary:** This study is for people with Duchenne Muscular Dystrophy (DMD), a condition that makes muscles weak. The study is testing a new medicine called WVE-N531, which is given through a needle in the vein (intravenous or IV). It aims to see if the medicine is safe and how well it works. Participants in this study must have a specific change (mutation) in their DMD gene that the medicine can help. The study has three parts, with Part A and Part B already completed. Now, new patients are being enrolled in Part C. During the study, participants will have muscle biopsies, which are small samples taken to check muscle health. They will receive doses every four weeks for up to one year. Researchers will measure a protein called dystrophin, which is important for muscle strength, and check for any side effects. **Key Points:** - The study lasts up to 1 year with doses every 4 weeks. - Participants need to undergo muscle biopsies. - Safety checks will continue for 10 months after the last dose. **Note:** Participants must meet certain health criteria and cannot have had major surgery recently or used certain substances.