This decrease in tau prion-like activity is concurrent with a decrease in tau phosphorylation, suggesting that biochemical events such as phosphorylation may affect prion-like tau formation or regulate tau toxicity, although whether the reduction of prion-like tau in elderly AD patients is due to the conversion of prion-like tau to a more inert amyloid state, such as total insoluble tau, or due to its reduced production and clearance is still unclear. Here, MAPT is linked to Alzheimer disease.