MAPT and Parkinson disease: However, even if elevated [11C]PBB3 is indeed representative of tau binding, this might not be surprising in view of recent evidence for early tau pathology in the nigrostriatal system of subjects with mild motor deficits insufficient to be diagnosed with PD, even without α-syn aggregates33, nor would this possibility have any impact on our interpretation that the pathology of PD starts in nerve terminals.