MAPT and Huntington disease: Regarding other neurodegenerative PMDs, it has been firmly demonstrated that tau (AD), alpha-synuclein (α-syn) (PD), mutant huntingtin (mHTT) (HD), and TDP-43 (ALS and FTLD) are transmitted between cells as well as between functionally connected brain regions [reviewed in Guo and Lee (2014); Vaquer-Alicea and Diamond (2019); Alpaugh et al. (2021)].