MAPT and early-onset autosomal dominant Alzheimer disease: In this study, we examined Alzheimer’s disease neuroimaging initiative (ADNI) participants who were unambiguously Aβ- based on both CSF Aβ42/Aβ40 and Aβ PET biomarkers in order to investigate how age, sex, APOE-ε4, and vascular risk factors associate with the earliest detectable CSF tau cross-sectionally and longitudinally, and whether elevation of CSF p-Tau can predict longitudinal hippocampal atrophy, hypometabolism, and cognitive decline.