MAPT and Alzheimer disease: Major reliable CSF and advanced blood-based biomarkers for pathological changes in AD are Aβ42 (often expressed as the Aβ42/Aβ40 ratio), total tau, phosphorylated tau, neurofilament light chain (NfL), the microRNA subtypes miR-21-5p and miR-451a, and glial fibrillary acidic protein (GFAP) [166,167].