Open-Label Study of mRNA-3927 in Participants With Propionic Acidemia

During the Dose Optimization Stage, after each dose cohort is fully enrolled (≥1 year of age), and the dose-limiting toxicity (DLT) observation window of at least 14 days is complete for the final participant in that cohort, the Sponsor will review the totality of available safety data in conjunction with all available PK/PD data. Based on this review, the Sponsor will recommend a revised dose and/or dosing interval. The Sponsor will abide by predefined constraints as to the maximum percentage change in dose and dose interval. A maximum of 9 cohorts will be enrolled in Part 1 (Dose Optimization). Upon establishment of a dose with an acceptable safety and PD activity in Part 1 (participants ≥1 year of age), additional participants will be enrolled into the study in Part 2 (participants ≥1 year of age) to allow for determination of the safety, efficacy, and PD of mRNA-3927. Part 3 will evaluate the safety, efficacy and PD response in infants (\<1 year of age). Participants in all the phases will participate in a predosing observational period, followed by a treatment period, and then a follow-up period after withdrawal of treatment.