A combined PET study utilizing [11C]DASB and [18F]DOPA, as markers of SERT and monoaminergic terminals function, respectively, revealed that PD subjects with EDS exhibited a reduction in SERT availability within the rostral raphe, locus coeruleus, thalamus and hypothalamus, as well as reduced [18F]DOPA uptake within the locus coeruleus, rostral raphe and ventral tegmental area (97). This evidence concerns the gene SLC6A4 and Parkinson disease.