MAPT and frontotemporal dementia: The absence of tauP301L aggregates or neurofibrillary tangles (NFTs) in neurospheres and in young mice, despite phosphorylation at many of the sites most frequently phosphorylated in AD and FTD (pSer202, pSer396, pSer235, pSer404) [36], [73]–[76], also may correspond to unbound tau as MT association has been implicated as an important step for tau nucleation [77], [78].