MAPT and frontotemporal dementia: PSP is associated with 4-repeat (4R) tau inclusions1,3; FTD is characterized by 3-repeat (3R)-only, 4R-only, or mixed (3R and 4R) tau inclusions or TAR DNA-binding protein 43 aggregates4; and AD is characterized by extracellular amyloid plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau (mixed 3R and 4R tau inclusions)5,6.