SLC6A3 and Parkinson disease: Despite this relative limitation, a previous study on DAT availability in the nigrostriatal system of early PD patients as quantified with [18F]FE-PE2I [9] showed changes of DAT availability in the SN compared to healthy controls that were still larger (30%) than the reliably detectable difference (~ 18%, based on effect size of n = 9), confirming that the assessment of the nigrostriatal system with [18F]FE-PE2I PET provides a comprehensive assessment of the PD pathophysiology in vivo.