[3H]KAC-50.1displayed a KD of 35 nM toward site 2 in recombinant α-syn fibrils.Specific binding of [3H]KAC-50.1 was observed in brain tissues withabundant α-syn pathology but also in AD, PSP, and CBD cases,indicating binding to amyloid β (Aβ) and tau pathology.PET studies showed a rapid entrance of [11C]KAC-50.1 intothe brain and relatively rapid washout from cortical brain regions,with slower washout in subcortical regions. Here, MAPT is linked to Alzheimer disease.