Finally, it should be noted that low brain dopaminergic activity has been associated with (a) homozygosity or heterozygosity for the Taq1 allele of the dopamine D2 receptor, which renders it less functional [148]; (b) disruptions to the sleep–wake cycle [149]; and (c) psychosocial stress [150] that each are associated with weight gain, glucose intolerance, and/or insulin resistance [148,151,152,153,154]. This evidence concerns the gene DRD2 and Glucose intolerance.