SLC6A3 and major depressive disorder: Several DAT imaging studies revealed an association between decreased striatal DAT availability and non-motor symptoms in PD including anxiety [251], depression [252,253,254], apathy [255], impulsivity [239,256], fatigue, constipation [240], hyposmia [257,258,259,260], autonomic symptoms [261,262,263,264,265,266], sleep disturbances, daytime sleepiness [267], body weight loss [268] and visual hallucinations [241], in support of a partial dopaminergic pathogenesis [269] (Table 1).