MAPT and early-onset autosomal dominant Alzheimer disease: The ATN (β-amyloid [Aβ], tau, neurodegeneration) system categorizes individuals based on the core Alzheimer disease (AD) fluid/imaging biomarkers, independently of cognition or clinical staging.1,2 Different combinations of normal (−) and abnormal (+) biomarkers result in 8 profiles under 3 main categories: normal (A−T−N−), non-AD pathologic change (tau or neurodegeneration in the absence of Aβ; A−T+N± or A−T−N+), and Alzheimer continuum (Aβ alone or together with other pathologies; A+T±N±).