There was no evidence that baseline DAT SBR predicted later apathy/anhedonia, and no evidence for an association with change-from-baseline DAT SBR (online supplemental figure S4, top); this is in contrast to the clear strengthening of association between absolute striatal DAT SBR and apathy/anhedonia score as PD progresses (online supplemental figure S4, bottom). This evidence concerns the gene SLC6A3 and Parkinson disease.