Oral microbiome dysbiosis in autism spectrum disorder: the oral-gut-brain axis and future perspectives: a narrative review

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with a steadily increasing global prevalence, yet its etiology remains largely unclear. Emerging evidence suggests that oral microbiome dysbiosis may contribute to the pathogenesis of ASD, potentially through the oral-gut-brain axis, although the exact role and causality remain to be fully established. In this narrative review, we synthesize recent clinical and metagenomic evidence on oral microbiome alterations in ASD and critically evaluate the potential pathways through which these microbial imbalances may impact neurodevelopmental outcomes. We summarize the key host-microbe interactions, including inflammatory signaling, epithelial barrier disruption, and immune-neural crosstalk, while emphasizing that direct causal evidence is still limited. Dysbiosis in individuals with ASD is characterized by altered microbial communities, including increased <i>Streptococcus</i> and decreased <i>Prevotella</i>, which correlate with clinical symptom severity. Moreover, metagenomic profiling has indicated the presence of potential biomarkers in the oral microbiome, which may serve as promising noninvasive diagnostic tools for ASD. While the clinical applications of oral microbiome diagnostics are still in the early stages, we explore the challenges and opportunities for developing these biomarkers for risk stratification. Finally, we outline future research directions that could enhance the understanding of the oral microbiome's role in ASD and facilitate the development of personalized intervention strategies.