MAPT and progressive supranuclear palsy: Endpoint-dilution analysis to quantitate 4R tau seeds indicates 105–107 seeding doses in progressive supranuclear palsy (PSP) cases as a 4R tauopathy, and some 4R tau seeding in select Alzheimer’s cases albeit at multi-log lower levels when compared to 3R/4R tau seeding levels (Supplementary Fig. 5, online resource).