Autism Spectrum Disorder and the Gut Microbiota in Children: A Systematic Review

Introduction: Differences in microbiota composition in children with autism spectrum disorder (ASD) compared to unaffected siblings and healthy controls have been reported in various studies. This study aims to systematically review the existing literature concerning the role of the gut microbiota in ASD. Methods: An extensive literature search was conducted using MEDLINE and EMBASE databases to identify studies (January 1966 through July 2019). Results: A total of 28 papers were included. The studies ranged from 12 to 104 participants who were aged between 2 and 18 years from various geographical areas. Majority of studies included faecal samples; however, 4 studies examined mucosal biopsies from different sites. The heterogeneity in ASD diagnostic methodology, gut site sampled and laboratory methods used made meta-analysis inappropriate. Species reported to be significantly higher in abundance in autistic children included Clostridium, Sutterella, Desulfovibrio and Lactobacillus. The findings are however inconsistent across studies. In addition, ­potential confounding effects of antimicrobial use, gastrointestinal symptoms and diet on the gut microbiota are unclear due to generally poor assessment of these factors. Conclusion: It is clear that the gut microbiota is altered in ASD, although further exploration is needed on whether this is a cause or an effect of the condition.