MAPT and Alzheimer disease: This study adds to the overall body of recent neuroimaging reports assessing Alzheimer’s disease biomarkers in CU elderly.6,7,9,11,29,30 It also supports recent findings that demonstrate tau-PET as an accurate prognostic marker in preclinical and prodromal Alzheimer’s disease.10 However, compared with these longitudinal studies, our study used the [18F]-MK-6420 PET tracer, focusing on imaging the medial temporal regions for the detection of very early tau in CU individuals.