MAPT and frontotemporal dementia: In a normal adult brain, there are comparable levels of 3R-tau and 4R-tau, but in patients with PSP and CBD, the neurofibrillary tangles are predominantly 4R-tau, whereas Pick bodies in FTD are predominantly 3R-tau and neurofibrillary tangles in AD contain both 3R- and 4R-tau isoforms.