Open-Label Extension of EDG-5506 in Participants With Becker Muscular Dystrophy

This is an open-label, treatment extension study to evaluate the safety, tolerability, and durability of effect in long-term dosing of sevasemten. EDG-5506-203 MESA will provide continued access to sevasemten treatment to participants with Becker muscular dystrophy who were previously enrolled in EDG-5506-002 ARCH, completed EDG-5506-201 CANYON and GRAND CANYON, or completed EDG-5506-202 DUNE.

Key Inclusion Criteria:

• Males with a diagnosis of BMD and participation in EDG-5506-002 ARCH, EDG-5506-201 CANYON and GRAND CANYON, or EDG-5506-202 DUNE. Participants are eligible if they complete the respective prior study visits as follows:

• EDG-5506-002 ARCH: Complete the final study Visit 27 [Month 24]; or, completion of the ET visit prior to Visit 27 [Month 24]
• EDG-5506-201 CANYON and GRAND CANYON: Complete the final study visit (Cohorts 1, 2, 4, and 5: Visit 12 [Month 12]; Cohort 6: Visit 11 [Month 18])
• EDG-5506-202 DUNE: Complete at least 36 weeks of open-label treatment (Visit 14 [Week 52])

Key Exclusion Criteria:

• Any clinically significant changes during or following participation in EDG-5506-002, EDG-5506-201, or EDG-5506-202 that would affect the potential safety of the participant to receive sevasemten.
• Receiving moderate or strong cytochrome P450 CYP3A4 inhibitors or inducers.
• Receipt of an investigational drug other than sevasemten within 30 days or 5 half-lives (whichever is longer) of dosing in the present study.

• Receipt of oral corticosteroids for the treatment of BMD in the previous 6 months.