An Extension Study to Evaluate the Long-Term Safety and Clinical Activity of mRNA-3705 in Participants Previously Enrolled in Other Clinical Studies of mRNA-3705

A Phase 1/2, Global, Open-Label, Extension Study to Evaluate the Long-Term Safety and Clinical Activity of mRNA-3705 in Participants Previously Enrolled in Other Clinical Studies of mRNA-3705

The primary objective of this study is to evaluate the long-term safety and clinical activity of mRNA-3705 administered to participants with isolated methylmalonic acidemia (MMA) due to methylmalonyl-coenzyme A mutase (MUT) deficiency who have previously participated in other clinical studies of mRNA-3705.

Participants with isolated MMA due to MUT deficiency who were previously enrolled in other clinical studies of mRNA-3705 will have the option to enroll into this extension study provided all eligibility criteria have been met. The study will include 2 periods: 1) Treatment Period and 2) Follow-up Period (up to 6 months after the last dose of study drug).

Treatment Period will continue unless one of the following occurs: mRNA-3705 receives marketing approval and reimbursement in the country of origin of the participant (following market approval and access being in place, all participants who wish to continue treatment will be offered mRNA-3705 through market access, with the intention of preventing treatment interruption. Other appropriate access program is offered as allowed by local regulation to continue treatment with mRNA-3705. Safety monitoring will be performed for all participants under treatment per market access requirements), the participant discontinues study drug, the participant is no longer receiving clinical benefit in the opinion of the Investigator, or Sponsor discontinues the development of mRNA-3705.

Inclusion Criteria:

• Completed the assigned dose regimen treatment time period in other clinical studies of mRNA-3705 or is eligible for early transition to this study because they missed more than 3 consecutive doses of study drug due to coronavirus disease 2019 (COVID-19) vaccination during Study mRNA-3705-P101 Part 1.
• Completed the End of treatment (EOT) Visit (or End of Study Visit in the case of unscheduled dosing) in Study mRNA-3705-P101 within 10 days of their first dose of mRNA-3705 in this extension study.

Exclusion Criteria:

• Not expected to receive clinical benefit from continued mRNA-3705 administration, in the opinion of the Investigator.
• Any clinical or laboratory abnormality or medical condition that, at the discretion of the Investigator, may put the individual at increased risk by participating in this study.
• History of liver and/or kidney transplant.

NOTE: Other inclusion and exclusion criteria may apply.