MAPT and Alzheimer disease: Significant progress has been made in the development of AD biomarkers, including medial temporal lobe atrophy on magnetic resonance imaging (MRI) (4, 5), temporoparietal hypometabolism or hypoperfusion on positron emission tomography (PET) (6, 7), alterations in cerebrospinal fluid amyloid, tau, and phosphorylated tau levels (8), amyloid-ligand PET (9), and most recently tau-ligand PET (10, 11).