However, the clinical assessment of AD is being supported increasingly by validated positron emission tomography (PET) imaging and cerebrospinal fluid (CSF) biomarkers accurately reflecting Aβ “A”, tau “T”, and neurodegeneration “N” pathologies, which have improved the accuracy in diagnosing AD during life, and provided evidence for a biological classification of the disease (AT[N]).1 This evidence concerns the gene MAPT and Alzheimer disease.