MAPT and tauopathy: However, studies of tau radioligands have so far not been proven to be particularly helpful in FTD, binding much more strongly to paired helical filament (PHF)-tau found mainly in Alzheimer’s disease70,71 than to other forms of tau found in the primary tauopathies such as progressive supranuclear palsy72–75 or corticobasal degeneration76–78.