MAPT and early-onset autosomal dominant Alzheimer disease: The 2018 National Institute on Aging and Alzheimer's Association Research Framework emphasizes basing the diagnosis of Alzheimer's disease (AD) on underlying pathologic processes and supporting the clinical diagnosis with the identification of biomarkers grouped into the categories of β amyloid burden, pathologic tau burden, and neurodegeneration; this is known as the AT(N) model1.