Furthermore, emerging evidence suggests that the extracellular space, which is cleared by the glymphatic system, acts as a conduit for neuron-to-neuron propagation and regional progression of Alzheimer’s disease tau pathology (Chesser et al., 2013; Ahmed et al., 2014; Medina and Avila, 2014; Lewis and Dickson, 2016; Wu et al., 2016). This evidence concerns the gene MAPT and Alzheimer disease.