Furthermore, they can be abnormal in other proteinopathies.2–5 However, studies indicate that the tau protein can be cleaved into multiple different fragments, which are actively secreted from cells and can therefore potentially be identified in CSF.6 7 In this study, we assessed the potential of novel CSF measures of different tau species as candidate biomarkers for FTD. Here, MAPT is linked to proteostasis deficiencies.