Pathologically, PSP is defined by the accumulation of tau protein in subcortical and cortical regions, (reviewed in Williams and Lees, 2009 [13]), showing substantial overlap with other neurodegenerative diseases characterized by tau accumulation and grouped under the generic name of tauopathies, including approximately one-half of all frontotemporal dementia (FTD) cases and Alzheimer's disease [14]. This evidence concerns the gene MAPT and frontotemporal dementia.