SLC6A4 and Parkinson disease: In this regard, it is of interest that a recent study using positron emission tomography (PET) and the selective SERT tracer [11C]labeled 3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)benzonitrile (DASB) demonstrated a non-linear loss of presynaptic serotonergic neurons across the clinical course of PD.