The main purpose of this study is to evaluate the long-term safety of mRNA-3927 administered to participants with propionic acidemia (PA) who have previously participated in Study mRNA-3927-P101 (NCT04159103).

The study will assess long-term safety of mRNA-3927. Participants with PA who were previously enrolled and completed the end-of-treatment (EOT)/early termination (ET) visit of the mRNA-3927-P101 study 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 (90 days after the EOT visit). All participants will enter the study receiving mRNA-3927 at the same dose and at the same dosing interval last received in the mRNA-3927-P101 study.

Inclusion Criteria:

• Participated in Study mRNA-3927-P101.
• Completed the EOT/ET visit in Study mRNA-3927-P101 and enroll in this study such that the first dose in this study is planned to be within 14±3 days of the last dose of mRNA-3927 in the mRNA-3927-P101 study.

Exclusion Criteria:

• Not expected to receive clinical benefit from continued mRNA-3927 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.