Global Open-Label Extension Study of Del-desiran for the Treatment of DM1

A Global Phase 3 Open-Label Extension Study to Assess the Long-Term Safety, Tolerability, and Efficacy of Intravenous Delpacibart Etedesiran (abbreviated del-desiran, formerly AOC 1001) for the Treatment of Myotonic Dystrophy Type 1

The study consists of a Screening Period of up to either 4-weeks or 8-weeks depending on the prior parent trial, and up to a 4-year Treatment Period. The anticipated duration is 50 months and 2 weeks (4 years and 2.5 months). Participants will receive an intravenous infusion of del-desiran at the clinical study site every 8 weeks for a total of 7 doses per year. The final dose will occur at Year 4, Visit 7, followed by a final assessment 8 weeks after the last dose. An additional subgroup of de novo participants will also be included in a Fixed-Dose PK cohort. An Independent Data Monitoring Committee (IDMC) comprised of members independent and external to the Sponsor will review safety, tolerability, and efficacy (as needed) data of this study at regular intervals.

FROM A PARENT STUDY Key Inclusion Criteria: * Completion of any prior AOC 1001 studies with satisfactory completion of dosing and follow-up assessments and satisfactory compliance with the protocol requirements of the parent study, as determined by the Investigator. Key Exclusion Criteria: * Breastfeeding, pregnancy, or intent to become pregnant during the study. * Unwilling to comply with contraceptive requirements. * Any new conditions or worsening of existing condition that in the opinion of the Investigator would make the participant unsuitable for the study. FIXED-DOSE PK COHORT Key Inclusion Criteria: * Clinical and genetic diagnosis of DM1 and clinically significant hand myotonia. Key Exclusion Criteria: * Breastfeeding, pregnancy, or intent to become pregnant during the study * Unwilling to comply with contraceptive requirements * Abnormal lab values, conditions or diseases that would make the participant unsuitable for the study * Diabetes that is not adequately controlled * History of decompensated heart failure within 3 months of screening. Participants with preexisting pacemaker/ICD are not excluded * Body Mass Index \> 35 kg/m2 at Screening * Recently treated with an investigational drug or biological agent Note: Additional protocol defined Inclusion and Exclusion criteria apply