MAPT and Alzheimer disease: Alterations of the gut microbiota are associated with abnormal brain Aβ deposition in both AD animal models (Chen et al., 2020, 2022) and humans (Cattaneo et al., 2017; Sheng et al., 2022), and the transfer of a healthy fecal microbiota reduces Aβ and tau pathology in AD animal models (Kim et al., 2020).