Thus, while in primary tauopathies there is a preferential accumulation of 3R, 4R or 3R + 4R tau depending on the disorder [4], in secondary tauopathies, including AD, tau is composed of and equimolar ratio of 3R and 4R tau (3R + 4R tau) [5] (Table 1). Here, MAPT is linked to Alzheimer disease.