MAPT and early-onset autosomal dominant Alzheimer disease: Several animal studies suggest microglial involvement in the spread of tau pathology.76-80 A recent study in patients with Alzheimer's disease used PET to examine microglial activation, Aβ deposition and tau propagation in Alzheimer's disease brains.81 The authors hypothesized that microglial activation drives tau propagation throughout the brain in a Braak-like pattern in Alzheimer's disease.