MMUT (Methylmalonyl-CoA Mutase) is a gene that encodes a mitochondrial enzyme crucial for energy metabolism. It catalyzes the conversion of methylmalonyl-CoA to succinyl-CoA, an important step in breaking down certain amino acids and fatty acids. This reaction supports the citric acid cycle and overall cellular energy production. Mutations in MMUT can result in methylmalonic acidemia (MMA), a rare metabolic disorder characterized by a toxic buildup of methylmalonic acid in the body.