MAPT and Alzheimer disease: Toward a biological definition of biomarker-based research framework for AD, the 2018 National Institute on Aging–Alzheimer’s Association working group has updated the ATN classification system (Jack et al., 2018), whose measures have different roles for definition and staging: A: Aβ biomarkers determine whether an individual is in the Alzheimer’s continuum; T: pathological tau biomarkers determine if an individual in the Alzheimer’s continuum has AD; and N: neurodegenerative biomarkers determine the staging severity of the Alzheimer’s continuum.