The National Institute on Aging and Alzheimer’s Association (NIA-AA) proposed, in 2018, some guidelines (termed ‘ATN’) for classifying AD based on biomarkers of amyloid pathology (A), tau pathology (T), and neurodegeneration (N) [72]: ‘A’ is measured by cortical amyloid PET ligand binding or CSF Aβ-42; ’T’ is measured by CSF phosphorylated tau or cortical tau PET ligand binding; and ’N’ is determined by CSF total tau, 18F-fluorodeoxyglucose PET, or brain atrophy on magnetic resonance imaging. This evidence concerns the gene MAPT and Brain atrophy.