This extension study will determine the long-term safety and effectiveness of mRNA-3705, a treatment for Methylmalonic acidemia (MMA), in patients who previously enrolled in and completed a prior mRNA-3705 study.

The purpose of this study is to find out more about mRNA-3705, a study drug that is being tested and is not approved by the U.S. Food and Drug Administration (FDA). In this study you will receive mRNA-3705, which is being developed to treat people with isolated MMA with MUT deficiency mRNA-3705. mRNA-3705 can only be used in a study like this one. We want to see what dose of the study drug is safe, how the study drug affects the function of cells, and how much study drug is in the blood after patients receive it.

The purpose of this study is to find out more about an investigational drug called mRNA-3927 (the study drug). An "investigational drug" is a drug that is being tested and is not approved by the U.S. Food and Drug Administration (FDA). We want to see how safe the study drug is and if it works for participants with propionic acidemia (PA).