MAPT and neurodegenerative disease: The vicious circle of spread, seed, and accumulation of misfolded protein aggregates within the central nervous system is not only restricted to prion protein PrP, but has also been reported for other proteins, such as Aβ, α-synuclein, and tau, that are able to form amyloidogenic aggregates which spread through the brain and cause distinct neurodegenerative diseases [3,45].