MAPT and tauopathy: Tau can be transmitted trans-synaptically from one neuron to another neuron, based on connectivity rather than on proximity, thus facilitating progression of tau pathology in tauopathies (Liu et al., 2012; Ahmed et al., 2014; Dujardin et al., 2014b; Lewis and Dickson, 2016; Goedert and Spillantini, 2017; Goedert et al., 2017; Mudher et al., 2017; Gibbons et al., 2019).