This is confirmed by a decrease in the concentration of L-DOPA and DA in the CFS [58], as well as by a decrease in the level of 18F-DOPA incorporation (positron emission tomography) into dopamine synthesis [51] and DAT binding (DAT scan) in nigrostriatal dopaminergic neurons in patients at risk of PD development [59]. This evidence concerns the gene SLC6A3 and Parkinson disease.