Abstract
BACKGROUND: A growing body of evidence highlights the significant role of disruptions in the brain-gut-microbiota axis in the pathogenesis of various mental disorders. However, the potential impact of the "oro- and nasopharyngeal (ONP) microbiota" on mental well-being has been largely overlooked. This is particularly significant, as the ONP microbiota constitutes one of the most complex microbial ecosystems in the human body. Dysbiosis in this region has been associated with systemic diseases, which may, in turn, contribute to disruptions in the gut microbiota. METHODS: In this study, we synthesized the current literature investigating differences in ONP microbial composition in people with various mental disorders, compared to healthy controls. We also conducted a meta-analysis on studies developing predictive models based on microbial profiles for the diagnosis of mental disorders. Out of 26 studies that met the inclusion criteria, 9 had constructed diagnostic models. RESULTS: Our findings suggest that, despite inconsistencies in reported microbial alterations, ONP microbial signatures could represent a preliminary avenue for exploring associations with mental disorders. Interestingly, the unique dysbiosis patterns reported in the studies demonstrated diagnostic accuracy for conditions including autism spectrum disorder (ASD) and obstructive sleep apnea (OSA). This systematic review and meta-analysis revealed that the microbial communities in the ONP region of individuals with mental disorders differ significantly from those of healthy individuals. Moreover, the alterations in the ONP microbiota appear to be specific to different mental health conditions, suggesting their potential utility in the detection of mental disorders and even the prediction of comorbidities in the future. CONCLUSIONS: Further prospective and experimental studies are needed, with careful control for confounders and consideration of heterogeneity, to advance our understanding of the role of the ONP microbiota in mental health. Additionally, future research should explore the relationship between ONP and gut microbial dysbiosis to provide a more comprehensive understanding of their interplay in mental health disorders.