SLC6A3 and major depressive disorder: Additionally, our findings were relatively specific to apathy/anhedonia with no significant relationship observed between striatal DAT SBR and general depressive symptoms in sensitivity analyses; although we note that the upper end of the 95% CI for general depression scores was near zero, and therefore, it is possible that a weak interaction exists which we did not have statistical power to detect, even in the large PPMI dataset.