SLC6A3 and Parkinson disease: As expected, at baseline striatal DAT SBR in PD participants was on average around half that of healthy controls; and there was evidence of a marked decline over time (mean±SD percentage reduction from baseline: year 1=−9.7%±17.4%, year 2=−16.6%±17.7%, year 4=−26.6%±18.4%; figure 1A).