1 ACE and Chao1 ↓; Shannon and Faith’s Phylogenetic Diversity↓; Compositional difference in PCoA. 2 Phylum level: Firmicutes and Actinobacteria ↓, Bacteroidetes ↑. 3 Genera level: Bifidobacterium, SMB53, Dialister, Clostridium, Turicibacter, Adlercreutzia, cc115 ↓; Blautia, Bacteroides, Alistipes, Phascolarctobacterium, Bilophila, Gemella ↑. 4 PiCRUSt: Metabolism and biosynthesis ↑, signal transduction and cell motility ↓. 5 Correlation analysis: Differentially abundant genera and CSF biomarkers (Aβ42/Aβ40, p-tau, p-tau/Aβ42) of AD. Here, MAPT is linked to Alzheimer disease.