MMA-101 is an AAV-based (adeno-associated virus) gene therapy for the treatment of MMA. AAV is one of the most common vectors used in gene therapy and is used in many cell types, such as the liver, muscle, and central nervous system. MMA-101 contains the gene for methylmalonyl-CoA (MMUT) that will express this protein in the liver, aiming to provide a long-term correction for mut subtype MMA patients. MMA-101 received rare pediatric disease designation from the FDA in October 2020.