Abstract:
Autism Spectrum Disorder (ASD) is increasingly recognized as a neurodevelopmental condition influenced by
complex interactions between genetic, immune, metabolic, and microbial factors. Growing evidence suggests
that the bidirectional gut–brain axis—linking intestinal microbiota, immune activity, and neural pathways—
plays a substantial role in behavioral and physiological regulation. A narrative synthesis was performed based
on publications indexed in PubMed, Scopus, and Web of Science (2015–2025) focusing on clinical and
translational studies that explored microbiota composition, immune and neurotransmitter modulation, and
therapeutic interventions targeting the gut–brain axis in ASD. Inclusion criteria comprised peer-reviewed
human or translational animal studies addressing microbial, inflammatory, and behavioral parameters. Based
on the analysis of published studies, consistent patterns indicate that intestinal dysbiosis and epithelial barrier
dysfunction contribute to systemic inflammation and altered neuroimmune signaling. Microbial metabolites
modulate serotonergic, dopaminergic, and GABAergic pathways, influencing sensory processing, social
interaction, and behavioral regulation. Integrated evaluation of clinical data shows small-to-moderate
behavioral improvements and stable gastrointestinal benefits following microbiota-targeted approaches such as
probiotics, psychobiotics, dietary modulation, and anti-inflammatory therapy. Behavioral domains most
responsive include irritability, aggression, and emotional regulation, while global ASD severity shows limited
change. These findings suggest that therapeutic modulation of the gut–brain axis acts primarily through
restoration of microbial balance and neurochemical stability rather than direct modification of core autistic
traits.
