In AD, tau lesions include neurofibrillary tangles (NFTs) in neuronal cell bodies, neuropil threads in neurites and dystrophic neurites in neuritic plaques; in electron microscopy, tau assemblies form mainly paired helical filaments (PHFs) that consist of both 3R and 4R isoforms (Figure 1B). The gene discussed is MAPT; the disease is Alzheimer disease.