Depression in PD is associated with nigral and mesolimbic dopaminergic pathway dysfunction with reduced ventral tegmental area (VTA), cingulate and amygdala volumes on MRI, and reduced [11C]RTI-32 DAT uptake in limbic regions in PD patients, with depression correlated with loss of dopamine projections from the VTA [24] and substantia nigra (SN) [25]. Here, SLC6A3 is linked to depressive symptom measurement.