DRD2 and obesity due to melanocortin 4 receptor deficiency: Several genes have been reported to be strongly associated with metabolic syndrome in patients with schizophrenia, such as the fat mass and obesity-associated gene (FTO), leptin and leptin receptor genes (LEP, LEPR), methylenetetrahydrofolate reductase (MTHFR) gene, catechol-o-methyl transferase (COMT) gene, insulin-induced gene (INSIG) 2, sterol regulatory element-binding transcription factor 2 (SREBF2) gene, dopamine receptor D2 gene (DRD2), and the serotonin receptor 2C gene (HTR2C) (87–90).