For example, Clostridium butyricum (CB) could improve cognitive impairment and Aβ deposition in APP/PS1 mice, reduce neuroinflammation mediated by microglia, and reverse the abnormal changes of gut microbiota (GM) and butyric acid, indicating that CB can play the role of anti-AD by regulating the GM–gut–brain axis (Sun et al., 2020). The gene discussed is APP; the disease is Alzheimer disease.