Composition of Gut Microbiota in Children with Autism Spectrum Disorder: A Systematic Review and Meta-Analysis

Abstract

Background: Autism spectrum disorder (ASD) is a public health problem and has a prevalence of 0.6%–1.7% in children. As well as psychiatric symptoms, dysbiosis and gastrointestinal comorbidities are also frequently reported. The gut–brain microbiota axis suggests that there is a form of communication between microbiota and the brain underlying some neurological disabilities. The aim of this study is to describe and compare the composition of gut microbiota in children with and without ASD. Methods: Electronic databases were searched as far as February 2020. Meta-analyses were performed using RevMan5.3 to estimate the overall relative abundance of gut bacteria belonging to 8 phyla and 17 genera in children with ASD and controls. Results: We included 18 studies assessing a total of 493 ASD children and 404 controls. The microbiota was mainly composed of the phyla Bacteroidetes, Firmicutes, and Actinobacteria, all of which were more abundant in the ASD children than in the controls. Children with ASD showed a significantly higher abundance of the genera Bacteroides, Parabacteroides, Clostridium, Faecalibacterium, and Phascolarctobacterium and a lower percentage of Coprococcus and Bifidobacterium. Discussion: This meta-analysis suggests that there is a dysbiosis in ASD children which may influence the development and severity of ASD symptomatology. Further studies are required in order to obtain stronger evidence of the effectiveness of pre- or probiotics in reducing autistic behaviors.

The microbial metabolitep-Cresol induces autistic-like behaviors in mice by remodeling the gut microbiota

“…Rather, we propose that GI exposure to p-Cresol triggers ASD behaviors by inducing a selective microbiota dysbiosis, which is sufficient to fully induce social behavior deficits and partially stereotypies upon transplantation to control mice. We indeed show that a p-Cresol-rich environment reduces bacterial b-diversity, as described in ASD patients [6][7][8] , and provides a selective growth advantage for several taxa, in line with a previous in vitro study 26 . The correlation between the abundances of 26 OTU and social behavior argues for a clear link between certain bacterial taxa and social abilities.…”

“…Children with ASD and concurrent GI symptoms exhibit more pronounced social impairments, sensory overresponsivity and anxiety compared to ASD peers without GI symptoms [3][4][5] . In addition, ASD patients exhibit gut microbiota dysbiosis characterized by reduced bacterial b-diversity and changes in the relative abundances of several bacterial taxa [6][7][8] . Dysbiosis in ASD patients is associated with altered urinary, plasmatic or fecal levels of microbial metabolites such as shortchain fatty acids (SCFA), indoles and tyrosine-derived metabolites [9][10][11][12][13][14][15][16] .…”

“…Also, p-Cresol urinary levels correlated with the severity of ASD behavioral alterations 11,12 . p-Cresol is the product of tyrosine degradation by the intestinal microbiota and mainly by Clostridioides difficile and other species from the Clostridioides genus 25,26 , which is more abundant in ASD patients [6][7][8] .…”

Changes in the Gut Microbiota of Children with Autism Spectrum Disorder

“…At the genus level, controversial findings were more often reported [Ho et al, 2020], though a meta-analysis reported five genera (Bacteroides, Parabacteroides, Clostridium, Faecalibacterium, and Phascolarctobacterium) more abundant in ASD children and two genera (Coprococcus and Bifidobacterium) significantly decreased [Iglesias-Vazquez et al, 2020]. In our study, two butyrateproducing genera, Clostridium clusters IV and XIVa, were less prevalent in the gut microbiota of autistic children compared to in the control group.…”

“…Indeed, the observed gut microbiota changes across ASD studies were often contradictory [Ho et al, 2020;Iglesias-Vazquez, Van Ginkel Riba, Arija, & Canals, 2020]. Bacterial phyla Bacteroidetes, Firmicutes, and Proteobacteria have been reported more abundant in ASD children [Iglesias-Vazquez et al, 2020], but some studies demonstrated an opposite result or no difference between children with ASD and healthy control [Ho et al, 2020].…”