MAOB and schizophrenia: Dopamine is catabolised in dopamine neurons and glial cells by monoamine oxidases (MAOs) and catechol-O-methyl transferase (COMT).7, 35, 36 Midbrain monoamine oxidase A (MAOA) and MAOB are expressed in human substantia nigra,37 and inhibition of MAOs contributes to amphetamine-induced psychosis.33 Thus, decreased synthesis of dopamine breakdown or reduced dopamine transport proteins in schizophrenia may contribute to hyperdopaminergia or to dopamine dysregulation.