MMUT (Methylmalonyl-CoA Mutase) is a gene that encodes a mitochondrial enzyme vital for energy metabolism. It catalyses the conversion of methylmalonyl-CoA to succinyl-CoA, a key step in the breakdown of certain amino acids and fatty acids. This reaction supports the citric acid cycle and overall cellular energy production. Mutations in MMUT can cause methylmalonic acidemia (MMA), a rare metabolic disorder characterised by a toxic build-up of methylmalonic acid in the body.