MAPT and Alzheimer disease: The overall utility of this tracer for in vivo selective and reliable detection of tau aggregates in non-AD tauopathies, however, seems very limited with the exception of certain tau mutations causing frontotemporal lobar degeneration (FTLD) characterized by tau aggregates [26] that contain all six isoforms of tau (three-repeat (3R) and four-repeat (4R)) [14] with PHF ultrastructure resembling NFT found in AD.