DRD4 and schizophrenia: In a postmortem study of schizophrenic brains, the expression of DRD4 mRNA was found to be three times higher in the prefrontal cortex.13 However, risperidone and haloperidol are known to increase the expression of DRD4,14 so further studies are needed to reveal those alterations in mRNA expression that are related to the pathogenesis of schizophrenia or the effect of antipsychotic agents.