As mentioned earlier, compelling evidence that tau malfunction or dysregulation alone can be sufficient to cause neurodegeneration came in 1998 from the identification of mutations in the MAPT gene on chromosome 17 that causes frontotemporal dementia with parkinsonism (FTDP-17) [140], making cytoskeletal abnormalities a pivotal mechanism in neurodegeneration in AD (mutations in the MAPT gene cause primary tauopathies, while AD is the most important secondary tauopathy with the MAPT gene itself not being mutated) [143,148]. The gene discussed is MAPT; the disease is semantic dementia.