MAPT and Alzheimer disease: In recent years, there have been remarkable advances in biomarker‐based diagnosis and monitoring of AD as a secondary 3/4R‐tauopathy (4RT), with specific biomarkers that can detect beta amyloid and tau aggregates in vivo via positron emission tomography (PET) imaging or determine pathophysiological amyloid and tau species in cerebrospinal fluid (CSF) or blood plasma.