Myopathy with lactic acidosis and sideroblastic anaemia (MLASA) is a rare autosomal recessive oxidative phosphorylation disorder specific to skeletal muscle and bone marrow. MLASA has been associated with a missense mutation in pseudouridylate synthase 1 (PUS1), an enzyme located in both nucleus and mitochondria, which converts uridine into pseudouridine in several cytosolic and mitochondrial tRNA positions and increases the efficiency of protein synthesis in both compartments. Recently, it has been reported that a mutation of the mitochondrial tyrosyl-tRNA synthetase gene, YARS2, also causes MLASA.
