MAPT and Alzheimer disease: The recent guidelines of the National Institute on Aging–Alzheimer’s Association (NIA-AA) Research Framework now define Alzheimer disease (AD) as a biological entity for which an in vivo diagnosis is no longer based solely on clinical diagnostic criteria but requires supporting evidence from PET or fluid biomarkers of AD-typical β-amyloid (Aβ) and tau pathology.1, -, 3 In contrast to PET, bodily fluid–based measurements can provide different molecular biomarkers from a single assessment and are more cost effective, widely attainable, and not limited by radiation exposure.