MAPT and Alzheimer disease: CSF of AD patients even in early phases of the disease shows decreased values of Aβ-42 and, together with increased total tau (tTau) or phosphorylated tau (pTau), suggests the presence of cognitive dysfunctions even in healthy elderly subjects [104, 105]; CSF tau/Aβ-42 ratio is a prediction of cognitive decline in non-demented older adults [106–110] and with MCI [110–113].