Academic journal article Shanghai Archives of Psychiatry

Characteristics of the Gastrointestinal Microbiome in Children with Autism Spectrum Disorder: A Systematic Review

Academic journal article Shanghai Archives of Psychiatry

Characteristics of the Gastrointestinal Microbiome in Children with Autism Spectrum Disorder: A Systematic Review

Article excerpt

1. Introduction

Autism spectrum disorders (ASD) refers to a range of neurodevelopmental disorders, primarily characterized by difficulties in social interactions, verbal and nonverbal communication, and stereotypic or repetitive behaviors. [1] Although the classification of ASD varies in different diagnostic systems, it essentially encompasses autism, childhood disintegrative disorder, Asperger's syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS). [2,3,4] The etiological pathways and pathogenesis of ASD remain unknown.

A high prevalence (23-70%) of Gastrointestinal (GI) distress, including abdominal pain, bloating, diarrhea and constipation, has been reported among children with ASD. [5] The high frequencies of these GI symptoms could reflect abnormal GI microflora in ASD children. There are more than 100 trillion symbiotic microorganisms [6] in the human GI tract that are important for nutrition and metabolic processes. Some evidence suggests that these same microorganisms also play a role in brain development, behavior, and gene expression via neural, endocrine, and immune pathways. [7] Emerging research on the gut-microbiome-brain connection in both mice and humans has shed new light on the pathogenesis of various mental diseases including ASD. [8,9] Nonetheless, whether GI microbiota contribute to the pathogenesis or the developmental course of ASD is still unclear. Previous clinical and pathological studies on microbes associated with the development and treatment of ASD have yielded inconsistent findings. To our knowledge, there has been no systematic review on this topic. The aim of the current study is to conduct a systematic review to evaluate and summarize findings from studies on the characteristics of the GI microbiome in children with ASD.

2. Methods

2.1 Data retrieval strategies

The process of identifying articles for inclusion in this review is shown in Figure 1. The following key words (in both English and Chinese) were used to search PubMed (1966-2013), Embase (1947-2013), PsycINFO (1966-2013), ISI web of knowledge (1994-2013), Ovid/ MEDLINE (1970-2013), the Cochrane Library (19672013), the Chinese National Knowledge Infrastructure (1979-2013) database, the Chongqing VIP database for Chinese Technical Periodicals (1989-2013), WANFANG DATA (1990-2013), and the China BioMedical Literature Services System (SinoMed) (1978-2013): autism (including 'Child Development Disorders, Pervasive', 'autis*', 'pervasive development* disorders*', 'child schizophrenia', 'kanner*', 'Rett*', 'Asperger*', 'zi bi zheng'[an older term for autism in Chinese!), 'bacteria', 'bacter*', 'microbiology', 'microbio*', 'microbiome', 'microbiome*', 'microbial', 'microorganism*', 'metagenomics', 'metagenome', 'metagenom*'. All articles published before October 5, 2013 were included in the search.

Identified articles were imported to Endnote X6 to remove duplicated records. Two authors (XC and CL) independently screened titles and abstracts of the remaining articles for potential inclusion. The full text of the articles were downloaded for further assessment when reviewers thought that the article met inclusion criteria or when reviewers were unsure about whether or not the article met the inclusion criteria. The references of all full-text articles were hand searched to identify other potential articles. These two authors then independently read the full-text articles and evaluated them according to the pre-defined inclusion or exclusion criteria listed below. These authors had disagreements about whether or not to include four articles; these disagreements were resolved through discussion.

2.2 Inclusion and exclusion criteria

All included studies: (a) were about the GI bacteria in children diagnosed with ASD; (b) had a group of children diagnosed with ASD, regardless of which diagnostic criteria were used (including but not limited to the Diagnostic and Statistical Manual of Mental Disorders [DSM1, [2] the International Statistical Classification of Diseases and Related Health Problems [ICD1, [3] and Chinese Classification and Diagnostic Criteria of Mental Disorders [CCMD1 [41); (c) had information about sample size and the prevalence of the specific bacteria assessed; (d) were written in English or Chinese. …

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