MAPT and Alzheimer disease: Decreased levels of CSF Aβ1–42 reflect Aβ burden in the brain as a result of its accumulation into plaques, whereas p‐tau181 and t‐tau have been suggested to reflect increased tau phosphorylation and general tau secretion from Aβ‐affected neurons (both appear predictive of AD‐type tangle pathology and neurodegeneration, respectively) (Molinuevo et al, 2018).