In addition, a recent meta-analysis was performed that was based on over 1000 association studies on schizophrenia, and this study highlighted 16 genes, which were mostly dopamine-related, including catechol-O-methyltransferase (COMT) and dopamine receptors D1, D2, and D4 (DRD1, DRD2 and DRD4) [9]. This evidence concerns the gene COMT and schizophrenia.