Although previously no change was found in AADC mRNA in the midbrain of schizophrenia patients,16 positron-emission tomography (PET) imaging studies have suggested increases in AADC activity in schizophrenia patients.11 Thus, further studies of TH and AADC within the basal ganglia are needed to determine whether molecular changes consistent with increased dopamine biosynthesis occur in schizophrenia. This evidence concerns the gene DDC and schizophrenia.