MAPT and frontotemporal dementia: Similar to our findings from DESCRIBE, tau ratios were lowest in PSP (median sEV 3R/4R tau ratio 0.38, IQR [0.33–0.50]), compared with all other groups (median sEV HC 1.02, IQR [0.96–1.06], PSP versus HC P < 0.00001; ALS 1.02, IQR [0.92–1.11], PSP versus ALS P < 0.00001; ALS–FTD 0.95, IQR [0.84–1.00], PSP versus ALS–FTD P < 0.00001; bvFTD 1.34, IQR [1.17–2.34], PSP versus bvFTD P < 0.00001) and highest in bvFTD, median sEV bvFTD versus all other diagnostic groups P < 0.00001) (Fig. 5a and Extended Data Table 3 (sEV), and Supplementary Fig. 16a and Extended Data Table 3 (mEV)).