Characteristics of the gastrointestinal microbiome in children with autism spectrum disorder: a systematic review

BACKGROUND: A high prevalence of gastrointestinal (GI) symptoms has been reported in children with Autism Spectrum Disorders (ASD). However, results from studies about the GI mircobiome of such children have been inconsistent. AIM: Integrate the results of studies that examine the distribution of different GI microorganisms in children with ASD. METHODS: Studies related to the GI microbiome in children with ASD were identified through PubMed, Embase, PsycINFO, ISI web of knowledge, Ovid/Medline, the Cochrane Library, the Chinese National Knowledge Infrastructure (CNKI) database, the Chongqing VIP database for Chinese Technical Periodicals, WANFANG DATA, and the China BioMedical Literature Service System (SinoMed). Studies were screened for inclusion following pre-defined inclusion and exclusion criteria. Software Review Manager 5.2.6 was used for statistical analysis. RESULTS: A total of 15 cross-sectional studies, all of which had relatively small samples, were included in the final analysis. Only one of the included studies was from China. Among the 15 studies, 11 studies (with a combined sample of 562 individuals) reported significant differences between ASD children and controls in the prevalence of GI bacteria, particularly bacteria in the Firmicutes, Bacteroidetes and Proteobacteria phyla. However, due to the substantial heterogeneity in methodology and the often contradictory results of different studies, it was not possible to pool the results into a meta-analysis. CONCLUSIONS: To date, studies on the GI microbiome in children with ASD are limited in quantity and quality. There does, however, appear to be a ‘signal’ suggesting significant differences in the GI microbiome between ASD children and children without ASD, so there would be value in continuing this line of research. To improve validity and decrease the heterogeneity of findings, future studies should enlarge sample sizes, standardize methods and assess relevant confounding variables, such as the severity of GI symptoms and the use of medications, special diets and supplements.