Background Recently, many reports indicated the role of the gut microbiome in the development of autism in young children. Microbes are capable of synthesizing small molecules like fatty acids and sugars which act as signalling molecules to activate/deactivate nervous system or even trigger an inflammatory response. Thus, the current review aims to explore the role of microbes in the development of autism, summarizing data from animal models and human studies.
Methods Referring to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, searches were performed in three databases (PubMed, ScienceDirect, Web of knowledge and; database inception to 31/12/2018) using ‘microbiome’ OR ‘microbiota’ combined with ‘autism’ as MeSH terms. All the titles and Abstracts retrieved were screened based on the inclusion and exclusion criteria. Studies reporting gut microbiome data in relation to the development of autism were included. Studies without gut microbiome data and/or reports on the evaluation on autism were excluded, along with reviews, conference Abstracts, case studies, and comments.
Results Out of the 2237 articles were accessed, seven studies were eligible for the qualitative analysis according to the inclusion criteria. Two studies described the murine model of autism, while the remaining five studies focused on children. One study revealed that there are no significant differences in gut microbiome among the three groups--severe, mild and healthy children, while three studies indicated that there is a higher abundance of Proteobacteria and Bacteroides in autistic children, with a reduced population of Firmicutes and Actinobacteria (figure 1). One study highlighted that higher Clostridiaceae species present in autistic children which explain for the development of autism in children as these species could produce toxic metabolic products (e.g., phenols, p-cresol, indole derivatives). Similar results were also observed in autistic animal models - there is increase abundance of Bacteroides, Parabacteroides, Sutterella, Dehalobacterium and Oscillospira genera.
Conclusions Altogether, these results revealed a positive correlation between dysbiosis and autism. Microbiome alterations may contribute to the development of autism, particularly via the production of toxic bacterial metabolites and alteration in immune function. By keeping the ‘healthy’ gut bacteria in check, these efforts could improve intestinal and mental health, easing and reducing autistic behaviour in children.
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