Table 1 outlines key features of the tau aggregates associated with different tauopathies. They can be classified into primary or secondary depending on whether tau aggregates represent the sole molecular lesion, or if the disease is associated with other pathological features, such as Aβ plaques in AD (73). Tauopathies can be further distinguished by the tau isoforms present in their filaments, with AD and CTE comprising all six isoforms (3R and 4R), CBD, PSP, and AGD only comprising only 4R isoforms, and PiD only containing 3R isoforms (67). This evidence concerns the gene MAPT and argyrophilic grain disease.