Association of Human Gut Microbiota with Alzheimer’s Disease Pathogenesis: An Exploratory Clinical Study

<b>Background/Objectives:</b> The gut-brain axis and its role in neurological disorders have garnered increasing attention in recent years. However, studies assessing the association between microbiota and Alzheimer's disease in Japanese cohorts are scarce. This study investigated the potential role of the brain-gut axis in Japanese patients with Alzheimer's disease (AD), focusing specifically on the role of microbiota composition in AD pathogenesis. <b>Methods:</b> Ten patients with AD and 21 healthy adults across three different age groups were enrolled. Fecal microbiota composition was assessed using 16S rRNA gene sequencing. <b>Results:</b> We found that some bacterial species, such as <i>Ruminococcus inulinivorans</i> and <i>Ruminococcus torques</i>, were more abundant in the AD group, whereas others-including <i>Agathobacter rectalis</i>, <i>Bacteroides uniformis</i>, and <i>Clostridium butyricum</i>-were relatively more abundant in healthy adults. However, individual taxa differences did not reach statistical significance. <b>Conclusions:</b> Although our preliminary findings suggest no significant differences in fecal microbiota compositions between patients with AD and healthy individuals, they suggest that microbiota can identify a potential risk for AD development. Future research may help elucidate the bacterial species associated with AD pathogenesis, potentially enabling the use of microbiota composition as a screening tool to identify healthy individuals and those with AD or preclinical AD-an increasingly critical goal amid rising global dementia rates and the urgent need for preventive strategies.