MAPT and Brain atrophy: This has been classified as the A/T/N system, where “A” refers to amyloid β (Aβ), that can be assessed by either PET imaging of amyloid plaques or cerebrospinal fluid (CSF) of Aβ42 or the Aβ42 to Aβ40 ratio; “T” refers to tau pathology and can be measured by CSF phosphorylated tau or tau PET imaging of parenchymal neurofibrillary tangles; “N” refers to neurodegeneration and can be evaluated as elevated levels of CSF total tau, decreased glucose metabolism detected by FDG-PET imaging, and brain atrophy by using structural MRI (Jack et al., 2018).