MAPT and Cognitive impairment: The biological spectrum of AD, whereby neuronal degeneration, deposition of tau, and Aβ can be detected [23], encompasses a wide range of clinical entities such as mild cognitive impairment (MCI) [24]), mild behavioural impairment [25]) and subjective cognitive impairment [26], which may represent the phenotypical underpinning of ongoing neurodegeneration [23].