As reviewed in [78] and [79], SNPs in the genes encoding serotonin receptors, serotonin transporter, dopamine receptors DRD2 and DRD4, catechol-O-methyltransferase (COMT), leptin and leptin receptor, ghrelin, melanocortin 4 receptor (MC4R), proopiomelanocortin (POMC), AgRP, oestrogen receptors ESR1 and ESR2/ESβ, brain-derived neurotrophic factor (BDNF), cannabinoid receptor 1 (CNR1), opioid receptor delta 1 (OPRD1), as well as fat mass- and obesity-associated gene (FTO) are associated with the risk of AN. This evidence concerns the gene OPRD1 and obesity due to melanocortin 4 receptor deficiency.