One of the earliest studies, however, was carried out by Eisensehret and colleagues who employed SPECT tracers [123I]IBZM and [123I]IPT-SPECT, as markers of post-synaptic dopamine type-2 receptors (D2R) density and presynaptic DAT, respectively, to gain an insight into striatal dopaminergic integrity in five patients with iRBD compared to 14 PD patients and seven controls (34). This evidence concerns the gene SLC6A3 and Parkinson disease.