MDH1 and schizophrenia: Previous research has implicated metabolic and mitochondrial genes [3,7,8,39,40], including ornithine aminotransferase (OAT) [7] and metabolic enzyme cytosolic malate dehydrogenase (MDH1) [3,41] in schizophrenia, which have not been shown to be influenced by cigarette smoking or antipsychotic treatment.