MAPT and Alzheimer disease: “A” biomarkers (amyloid positron emission tomography [PET], CSF Aβ) support the diagnosis of AD; “A” and “T” (tau PET; CSF phospho-tau) biomarkers are pharmacodynamic biomarkers that can be used to demonstrate target engagement with Aβ or tau species; and “N” (magnetic resonance imaging [MRI], fluorodeoxyglucose PET, CSF total tau) biomarkers are pharmacodynamic markers of neurodegeneration that can provide evidence of neuroprotection and disease modification [33].