Besides dopamine (DA), three further key neurotransmitters have been described to be involved in the pathogenesis of PD; namely noradrenaline (NA), acetylcholine (ACh), and serotonin (5HT).1,2 Consequentially, non-motor symptoms (NMS) in PD can potentially be related to dopaminergic, non-dopaminergic pathogenesis or a combination of both.1,3 Individual studies indicate that apathy,4 anxiety5 as well as aspects of sleep disturbances6 appear to be linked to striatal dopaminergic deficiency as measured by dopamine transporters (DaT) scans. This evidence concerns the gene SLC6A3 and Parkinson disease.