MAPT and Alzheimer disease: Advances in the detection of biofluid measures of AD pathology and neurodegeneration, including blood-based and CSF measures of total tau9, phosphorylated tau species (including phosphorylation sites at position 181 and 217)5,10–13, and neurofilament light chain (NfL)14–19 have the potential to bridge this gap and provide complementary information to that provided by biomarkers of β-amyloid burden.