To assess the abundance of neuron-derived exosomal α-synuclein in unrelated neurodegenerative diseases, we included patients with FTD (n=65) which is pathologically characterised primarily by tau or TAR DNA binding protein 43 (TDP-43) aggregation, and patients with PSP (n=35) and CBS (n=45) who present with atypical parkinsonism and pathologically are characterised by fibrillar aggregates of four repeat tau. Here, MAPT is linked to frontotemporal dementia.