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Introduction: There have many reported differences in the gut microbiota composition in children with autism spectrum disorder (ASD) compared to typically developed (TD) healthy cohorts (HC). This study aims to review existing literature and current studies regarding the role of the gut microbiota in the development of ASD. Additionally, this study aims to determine if there is a correlation between gut microbiome dysbiosis and an increased severity in ASD symptoms. Methods: An extensive literature search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) system. A total of 7 databases including PubMed and MEDLINE were used and a total of 591 records were screened and assessed for eligibility. Results: A total of 10 papers were included. The studies ranged from 6-143 participants with ASD who were between the ages of 2 to 13 years old and were from various geographical locations throughout the world including China, the United States, and Slovakia. Also included in this study is one study that includes an animal model of 7-week-old BTBR and B6 mouse models. All the studies included collected fecal samples. Studies reported to be significantly higher in abundance in autistic children included Bacteroides spp., Firmicutes, and Prevotella spp. A significant decrease in the abundance of Streptococcus and Lactobacillus was also observed in the studies. The findings are inconsistent across studies as research is limited on the gut microbiome in children with ASD and the role of gut dysbiosis on the severity of ASD and related behavioral symptoms. Conclusion: A clear connection between the diversity of the gut microbiome and the severity of ASD symptoms in children has been demonstrated through review of the research. It can be determined that a greater diversity of gut microbiota is associated with improved behavioral and gastrointestinal (GI) outcomes in children with ASD. Gut microbiota is altered in children with ASD; however, further exploration is needed to



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