MAPT and proteostasis deficiencies: While observations with [18F]AV1451 and [11C]PBB3 remain to be validated in ante-/post-mortem studies, they raise concerns that the different tau tracers might bind in vivo to multiple β-sheet structures, a finding that would limit their clinical utility in discriminating between both different protein deposits—which regularly coexist in different proportions in the neurodegenerating brain irrespective of the driving pathology [144]—and different proteinopathies.