Consistent with the dopamine-melatonin hypothesis, traits associated with SOB have also been linked to genetic polymorphisms in the dopamine system. These include BMI [32]–[34], eating disorders [35]–[37], blood pressure [38], fertility [39]–[41], novelty seeking [42], [43], [but 44], and sensation seeking [45]. Additionally, there is evidence of interactions between SOB and specific genetic polymorphisms, such as the dopamine receptor D4 (DRD4) 48 bp VNTR polymorphism, on psychiatric disorders [46], [47] and BMI [5]. In fact, SOB effects may be directly related to DRD4. In the retina DRD4 mRNA has been found in photoreceptor cells that indirectly control melatonin synthesis and have a regulatory role on light sensitive cyclic adenosine monophosphate [48]–[51]. Additionally, dopamine has been found to inhibit retinal melatonin synthesis via D2/D4 receptors but not through D1/D5 receptors [52].
