MAPT and Alzheimer disease: Although AD is the most extensively studied tauopathy, its classification as a secondary tauopathy complicates efforts to clarify the independent mechanisms of tau hyperphosphorylation due to significant interactions with coexisting pathologies, particularly Aβ.[13] These interdependent pathologies make AD less suitable for examining tau hyperphosphorylation as an independent process or for identifying common mechanisms shared across tauopathies.