Propionic acidemia is a genetic metabolic disorder characterized by metabolic acidosis, ketosis, vomiting, lethargy, cognitive impairment, and risk of death. It results from loss of function of the mitochondrial enzyme propionyl-CoA carboxylase and can be due to disease-causing variants in the PCCA gene, leading to accumulation of propionyl-CoA and its toxic metabolites. The purpose of this trial is to evaluate the safety and potential therapeutic benefit of an AAV-based gene therapy for propionic acidemia in patients with genetically confirmed biallelic variants in PCCA.