MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer disease (AD) is a progressive cognitive disorder leading to dementia1 in which the brain gradually accumulates both amyloid-β (Aβ) and tau pathologies.2 Autopsy studies identified the early stages of Aβ and tau pathologies in individuals who were clinically normal during life, representing a preclinical stage of AD.3 Based on autopsy studies,4 the prevailing research hypothesis posits that Aβ precedes and accelerates neocortical tau pathology, which together precipitate cognitive decline.