Since DAT imaging is a sensitive imaging tool to detect PD in an early disease stage (11) and there is consensus that subjects having scans without evidence of dopaminergic deficit show a much slower motor deterioration than subjects whose scans do show dopaminergic degeneration (33,48), the European Medicines Agency has qualified DAT imaging as an enrichment biomarker for clinical trials targeting early stages of PD (i.e., within 1–2 y of clinical diagnosis) (16). The gene discussed is SLC6A3; the disease is Parkinson disease.