Many studies have demonstrated the impact of intestinal microbiota on normal brain development. Moreover, the gut microbiota is impacted by multiple endogenous and environmental factors that may promote gut dysbiosis. An increasing number of studies are investigating the possible role of the gut dysbiosis in the development of neurological and behavioral disorders. For autism spectrum disorders (ASD), specific intestinal bacterial signatures have been identified, knowing that gastrointestinal symptoms are frequently found in ASD.
In this review, the peri and post-natal factors modulating the gut microbiota are described and the specific gut bacterial signature of ASD children is detailed. Through bidirectional communication between the gut microbiota and the brain, several mechanisms are involved in the development of ASD, such as cytokine-mediated neuroinflammation and decreased production of neuroprotective factors such as short-chain fatty acids by the gut microbiota. Imbalance of certain neurotransmitters such as serotonin or gamma-aminobutyric acid could also play a role in these gut-brain interactions.
Some studies show that this gut dysbiosis in ASD is partly reversible by treatment with pre- and probiotics, or fecal microbiota transplantation with promising results. However, certain limitations have been raised, in particular concerning the short duration of treatment, the small sample sizes and the diversity of protocols. The development of standardized therapeutics acting on gut dysbiosis in large cohort could rescue the gastrointestinal symptoms and behavioral impairments, as well as patient management.