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Abstract

Background: Children with Autism Spectrum Disorder (ASD) often experience gastrointestinal symptoms, prompting interest in the gut–brain axis and the potential role of gut microbiota in ASD pathology. To systematically review human studies from 2015–2025 comparing gut microbiota in children with ASD to neurotypical controls.
Methods: We reviewed global observational and clinical studies involving children aged 2–18 that assessed gut microbiota using DNA-based methods, primarily 16S rRNA sequencing. Outcomes included microbial diversity (alpha and beta) and taxonomic composition.
Results: Most studies reported altered gut microbiota in ASD. Alpha-diversity was frequently lower in ASD, indicating reduced microbial richness, though not universally. In contrast, beta-diversity consistently showed distinct microbial community structures between ASD and control groups. Common compositional findings in ASD included reduced Bifidobacterium and Prevotella, and increased Clostridium, Desulfovibrio, Sutterella, and other Proteobacteria. These shifts may contribute to immune activation, GI inflammation, and neuroactive metabolite production (e.g., short-chain fatty acids, lipopolysaccharide), potentially influencing ASD symptoms.
Conclusions: Evidence supports the presence of gut dysbiosis in children with ASD, marked by decreased beneficial microbes and increased potentially pro-inflammatory taxa. While findings vary by region and methodology, the microbiota appears to play a role in ASD via metabolic and immune-mediated mechanisms. The gut microbiome may serve as both a biomarker and therapeutic target in ASD, but further large-scale, standardized studies are needed