MAPT and Alzheimer disease: It has been suggested that tau secretion by microglia follows an exosome-dependent pathway.76,77 Tau-carrying exosomes have been detected in CSF and blood samples from patients with Alzheimer's disease and frontotemporal dementia.82,83 To confirm that exosome release mediates tau propagation, Asai et al. 76 inhibited microglial exosome synthesis in transgenic P301S mice (these mice express human tau associated with frontotemporal dementia with parkinsonism), which led to a severe decline of pathological tau in the brain.