While up to 70 % loss in patients with early PD occurs in the putamen, high-resolution PET showed that the DAT signal in the substantia nigra (SN) can be quantified, but with much lower abnormality, indicating that the integrity of the SN cell bodies is relatively preserved and that in PD mainly the terminals are affected in the early disease course. This evidence concerns the gene SLC6A3 and Parkinson disease.