Gut microbiota alterations in autism spectrum disorder: Implications for microbiota‑gut‑brain axis mechanisms and therapeutic strategies (Review)

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition often accompanied by chronic gastrointestinal (GI) disturbances. Recent evidence suggests that these GI issues may be biologically linked to ASD through the microbiota‑gut‑brain axis (MGBA). The present review aimed to highlight how alterations in the gut microbiota contribute to ASD symptoms and to explore potential microbiome‑based therapeutic strategies. Recent research findings regarding gut microbial composition in individuals with ASD were reviewed, focusing on changes in beneficial and harmful microbial taxa, associated inflammatory and metabolic alterations, and their implications for neural signaling within the MGBA. Data on emerging therapeutic interventions, such as probiotics, prebiotics, and fecal microbiota transplantation, were also evaluated. Studies reveal notable microbial dysbiosis in ASD, including reduced levels of Bifidobacterium and Prevotella and an increased abundance of Clostridium species. These alterations are linked to intestinal inflammation, impaired gut barrier integrity, and disturbances in neurotransmitter production. Furthermore, the highly restricted dietary patterns and food selectivity commonly observed in individuals with ASD are likely to reduce microbial diversity, particularly affecting fiber‑dependent taxa, such as Prevotella. Concurrently, the severity of specific ASD traits, particularly repetitive and rigid behaviors, has been closely correlated with GI discomfort and distinct microbial imbalances. Microbial metabolites, such as short‑chain fatty acids, appear to influence brain function, mood, and social behavior. Initial therapeutic trials indicate that microbiota‑targeted interventions may improve both GI symptoms and behavioral outcomes. Current evidence supports a significant association between alterations in the gut microbiota and ASD pathophysiology via the bidirectional MGBA. While further studies are required to establish causality and refine therapeutic approaches, emerging microbiota‑based treatments highlight the importance of adopting a holistic model that integrates neurological, immunological, and microbial aspects in understanding and managing ASD. However, the strength of mechanistic evidence varies across immune, neural, and endocrine pathways, with immune‑related mechanisms supported by the most consistent ASD‑specific data.