Autism spectrum disorder (ASD) is a public health problem with a prevalence of 0.6%–1.7% in children and is steadily increasing with recent data suggesting that as many as 1 in 59 children are diagnosed with ASD. Males are also up to 4 times more likely than females to be diagnosed with ASD.
Children with ASD struggle with social communication and interaction and are characterized by restrictive and repetitive behaviour patterns, interests, or activities. As well as psychiatric symptoms, dysbiosis and gastrointestinal comorbidities are also frequently reported. In support of this large studies (meta analysis) suggests that ASD children have gut dysbiosis (microbial imbalances) in both the type and abundance of gut bacteria which may influence the development and severity of ASD symptoms .
The prevalence of gastrointestinal symptoms such as constipation, abdominal pain, diarrhea, gas, and vomiting ranges from 9% to 90% in people with ASD, which is a much higher rate than in individuals without autism. Some studies have even observed an association between the gut symptoms and the severity of the clinical manifestations of the ASD, which means that the autistic symptoms would be more frequent and severe in children with more severe gut problems than in those without.
Current scientific thinking shows that the gut microbiota plays a role in brain development and function through the endocrine, immune, and nervous systems. Therefore alterations in the gut microbiota could trigger not only some of the GI symptoms that autistic children suffer from but also some of their neuropsychiatric symptoms.
Human studies have shown that children exposed to maternal inflammation during pregnancy have an increased risk for ASD. Since then, promising results from landmark animal studies have revived considerable interest in linkages between ASD and the gut microbiome. These animal studies have provided new evidence on mechanisms by which inflammation and gut microbiota influence neurobehaviors. For instance, pregnant mice with intestinal bacteria that induced activation of the maternal immune system, termed maternal immune activation (MIA), produced offspring with impaired sociability and repetitive behaviours, reminiscent of ASD symptoms in humans.
Animal studies have also shown that changes in microbiota lead to changes in behaviours. Raising animals without any gut microbial colonization, called germ free or gnotobiotic environment, resulted in abnormalities in a variety of complex behaviours. For example, germ-free mice tended to exhibit decreased sociability and less propensity to interact with unfamiliar partners. On a positive note reintroduction of bacterial strains or restoration of gut microbial ecology in these mice resulted in normalization of social behaviours. In one study, treatment with the gut bacterium Lactobacillus reuteri (L. reuteri) alone sufficiently reversed ASD-like symptoms in mice. Alteration of the postnatal gut microbiota by early life treatment with the human gut bacterium Bacteroides fragilis (B. fragilis) also sufficiently fixed deficits in communicative and stereotypic behaviour in mice offspring exposed to MIA.
While a recent study showed that postnatal colonization with human “infant-type” Bifidobacterium species showed improved behaviours for gnotobiotic mice. Together, these animal studies have hastened interest in human studies comparing gut microbiota between individuals with and without ASD.
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References
Nutrients. 2020 Mar; 12(3): 792. doi: 10.3390/nu12030792 PMCID: PMC7146354
PMID: 32192218 Composition of Gut Microbiota in Children with Autism Spectrum Disorder: A Systematic Review and Meta-Analysis
Lucía Iglesias-Vázquez,1 Georgette Van Ginkel Riba,2 Victoria Arija,1 and Josefa Canals2,*
Gut Pathog. 2020; 12: 6. doi: 10.1186/s13099-020-0346-1 PMCID: PMC6996179 PMID: 32025243 Gut microbiota changes in children with autism spectrum disorder: a systematic review Lucius Kang Hua Ho,1 Valerie Jia Wei Tong,1 Nicholas Syn,1 Niranjan Nagarajan,1,2 Elizabeth Huiwen Tham,4,5 Stacey K. Tay,4,5 Shefaly Shorey,6 Paul Anantharajah Tambyah,7,8 and Evelyn Chung Ning Law
