MAPT and Alzheimer disease: The AT(N) system, proposed by the NIA–Alzheimer’s Association (NIA-AA), categorizes AD biomarkers into three primary groups: A (amyloid deposition, e.g., CSF/plasma Aβ42, amyloid PET), T (tau pathology, e.g., CSF/plasma p-tau, tau PET), and N (neurodegeneration, e.g., total tau, NfL, GFAP, FDG-PET, MRI) [426–428].