MAPT and Alzheimer disease: Several noteworthy studies, including in vivo animal-PET studies using transgenic AD mouse models and in vivo human PET (positron emission tomography) studies in families carrying autosomal dominant Alzheimer’s disease (ADAD) mutations, have collectively shown that reactive astrogliosis is markedly increased in the early stages of AD progression cascades, even before the deposition of Aβ and tau, and the onset of neurodegeneration [30].