While in AD, no mutations have been identified in the MAPT gene encoding tau, until today, over 40 intronic and exonic mutations have been identified in FTD with Parkinsonism linked to chromosome 17 (FTDP-17), a form of FTLD-Tau (Hutton et al., 1998; Poorkaj et al., 1998; Spillantini et al., 1998) (Figure 1). Here, MAPT is linked to frontotemporal dementia.