MAPT and Alzheimer disease: The research framework for preclinical AD [13, 14] recently proposed a descriptive system, based on a categorical classification of biomarker positivity (A/T/N): “A” refers to amyloid pathology, assessed by either Aβ42 or the Aβ42/Aβ40 ratio in CSF or amyloid PET; “T” refers to tau pathology, assessed by CSF phospho-tau or PET with tau tracer; and “N” refers to neurodegeneration, assessed by CSF total tau, MRI, or FDG-PET.