DRD2 and obesity due to melanocortin 4 receptor deficiency: DRD2 TaqIA has been extensively investigated in neuropsychiatric disorders with presumed dopaminergic dysfunction, and the A1 allele has been associated with increased risk for disorders like substance abuse and pathological gambling or obesity, whereas the A2 allele has been implicated in the genetic risk for schizophrenia (Comings et al., 1996; Noble, 2003; Dubertret et al., 2004; Klein et al., 2007; Wang et al., 2013).