SLC6A3 and Parkinson disease: In patients whose striatal DAT SBR is particularly low, there is a scope to monitor apathy and anhedonia symptoms, or to intervene early with interventions such as behavioural activation therapy which has been shown to be potentially effective in treating these symptoms in PD.43 However, further validation of striatal DAT SBR as a potential marker of apathy/anhedonia risk is needed, especially as the Robin-Hood algorithm used in the two-lines test primarily tests for the presence of a threshold effect and cannot precisely identify the true turning point value.