MAPT and Alzheimer disease: Recent studies have shown that the gut microbiome profiles are distinct between preclinical AD patients and healthy individuals, and the gut microbiome profiles and specific taxa are correlated with amyloid-β (Aβ) and tau pathological biomarkers in the brain and the plasma Aβ42/Aβ40 ratio, suggesting that changes of the gut microbiome may occur early in the disease process before neuronal injury [24, 25].