MAPT and early-onset autosomal dominant Alzheimer disease: In this study, we use the high-affinity tau-PET tracer [18F]-MK-6420, focusing on imaging the medial temporal regions to detect very early tau in CU elderly, as opposed to the temporal meta-region of interest for later tau aggregation, at levels observed in Alzheimer’s disease.10 Specifically, we examined the prognostic accuracy of baseline [18F]-MK-6420 PET for predicting longitudinal memory decline in initially CU elderly, who have been stratified based on the presence of a tau-PET signal in the medial temporal lobe.