The mechanisms of transcellular tau propagation are understood best in the context of AD, where tau pathology is transmitted through the synaptic junction via the secretion of tau seeds by a presynaptic neuron and their subsequent reuptake by post-synaptic neurons (Goedert et al., 2017b; Mudher et al., 2017; Wang et al., 2017). This evidence concerns the gene MAPT and Alzheimer disease.