MAPT and semantic dementia: Tauopathies are classified based on the predominant tau isoform present in paired helical filaments (PHFs), e.g. Pick’s disease is characterized by 3-repeat (3 R) tau isoforms, whereas progressive supranuclear palsy (PSP) and some frontotemporal lobe dementias (FTLDs) are characterized by 4 repeat (4 R) tau isoforms.