Consequently “prion-like” mechanisms and the prion strain phenomena have become a major research focus in other neurodegenerative conditions, in particular, in Alzheimer’s disease (AD) and Parkinson’s disease where propagating assemblies of amyloid-β, tau and α-synuclein are being studied (Prusiner, 2013; Goedert, 2015; Collinge, 2016; Walker, 2016; Qiang et al., 2017; Condello et al., 2018; Peng et al., 2018; Vaquer-Alicea and Diamond, 2019). This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.