The role of microbiota in autism spectrum disorders

Autism spectrum disorder (ASD) defines a set of neurodevelopmental disorders characterized by persistent deficits in social communication and interaction, along with repetitive patterns of behavior. Symptoms generally appear in the early developmental period and cause significant impairment in individual and social functioning. In recent years the increased prevalence of ASD, along with the evidence of a significant link between autism and gastrointestinal (GI) disturbances, raised a special interest in exploring the reciprocal influences between gut and brain. Investigators highlighted the existence of a so-called "gut-brain axis," empowering the hypothesis that GI abnormalities could trigger neuropsychiatric symptoms in ASD. Intestinal microbiota is thought to play a pivotal role in gut and systemic homeostasis, in central nervous system development, as well as in behavioral modulation and recurrent microbial imbalances have been shown in gut microbiota of autistic people. In this review we analyze current knowledge about intestinal microbiota and the relevance and role of dysbiosis in ASD. The most accredited theories about gut-brain interaction will be reviewed, along with current scientific evidence supporting the relationship between microbial imbalances and impairment of neurodevelopment. Finally, we will focus on the results of different therapeutic approaches in this context: administration of pre- and probiotics, antibiotics, fecal microbiota transplantation and special diets and dietary supplements.