MAPT and tauopathy: In different tauopathies, different tau isoforms are implicated, for example 4R isoforms aggregate in tauopathies such as PSP, CBD and others,40 whilst 3R isoforms aggregate in tauopathies like PiD.41 Additionally, in some familial tauopathies point mutations in tau have also been identified.42 To investigate the effect of such differences in primary sequence on the Raman fingerprint of tau fibrils, we generated fibrils from the largest tau isoform (2N4R), the shortest naturally occurring isoform (0N3R), and 2N4R tau with a single point mutation (P301S).