The Role of the Gut Microbiome in Autism Spectrum Disorder
Autism spectrum disorder (ASD) is a complex biological neurodevelopmental disorder that is estimated to affect 1 in 100 children worldwide (World Health Organization (WHO)., 2023). Due to its broad-spectrum, signs often have a high individual variability, however, those with ASD commonly have difficulties relating to social, behavioural and communication skills (WHO., 2023). Gastrointestinal symptoms, such as abdominal pain, flatulence and bloating, are often a comorbidity in those with ASD, however, the underlying cause is unknown. Research suggests that gastrointestinal complaints and neuro-behavioural traits in ASD could be linked to gut microbiome composition and via the two-way communication between the gut and brain, called the gut-brain axis (Fattorusso et al., 2019). In this Research Spotlight, we will explore ASD in relation to the gut microbiome and delve into a study looking at the impact of Bimuno® GOS on 30 children with ASD (Grimaldi et al., 2018).
Gut-brain connection
It is well known that the gut microbiome plays an important role in health (de Vos et al., 2022). The gut-brain axis, in particular, has been of increasing interest due to its ability to impact gastrointestinal function, mood and cognitive health (Appleton., 2018). As research has progressed and more is understood about the gut-brain connection it is thought that this could explain some of the neurodevelopmental deficits and comorbid gastrointestinal disturbances seen in ASD (Li et al., 2016).
Those with ASD often have alterations in their gut microbiome profiles that are consistent with dysbiosis, however, it is not yet known the distinct microbiome profile that is specific to individuals with ASD (Fattorusso et al., 2019). Interestingly, research has revealed that Clostridiumbacteria are often overabundant in the colons of those with ASD compared to neurotypical individuals and could be associated with certain autistic traits and comorbidities (Kandeel et al., 2020). In particular, those with ASD exhibit high levels of Clostridium difficileand Clostridium clostridioformenot found in neurotypical children, and these strains are considered to be pathogenic strains of bacteria with opportunistic characteristics (Dehoux et al., 2016; Kandeel et al., 2020; Khanna and Gupta., 2019).
ASD and GI complaints
Common gastrointestinal complaints reported in those with ASD, such as constipation, diarrhoea and abdominal pain, are associated with changes in the composition of the gut microbiome (Ristori et al., 2019). Many functional gastrointestinal disorders that feature these common issues have been linked to the gut microbiome and a lower abundance of beneficial bacteria, such as bifidobacteria (Ristori et al., 2019). Along with higher levels of Clostridiumbacteria, many children with ASD also have a lower relative abundance of bifidobacteria in the gut, suggesting a possible link between the gut microbiome and comorbidities of ASD (Argou-Cardozo and Zeidán-Chuliá., 2018; Ristori et al., 2019).
Children with ASD who also have comorbid gastrointestinal disturbances tend to exhibit more severe behavioural changes, such as irritability and social withdrawal, and these neurobehavioural symptoms are thought to have an underlying inflammatory pathophysiology (Fattorusso et al., 2019). The inflammation hypothesis in ASD suggests the presence of immune system dysfunction in its development (Hughes et al., 2022). Up to 80% of immune cells are found in the gut, and gut barrier function plays a key role in immune homeostasis (Wiertsema et al., 2021). Given that gut barrier integrity and function can be influenced by gut microbiome composition and crosstalk along the gut-brain axis, it is important to note that dysbiosis, such as what is seen in ASD, can lead to changes in immune system function (Erbescu et al., 2022; Levy et al., 2017).
Research Spotlight: ASD and Bimuno® GOS
In this Research Spotlight, we highlight a study looking at the effects of different diets and supplementation with Bimuno® GOS in autistic children across a 10-week period (Grimaldi et al., 2018). This randomised, double-blind, placebo-controlled parallel study saw 30 children aged 4-11 years with ASD divided into two dietary groups: one excluding gluten and casein (exclusion group) and one group without restriction (non-exclusion). These groups were further divided into another 2 groups and supplemented with either Bimuno® GOS or placebo (maltodextrin) for 6-weeks. The protocol followed a 2-week run-in, 6-week feeding period and a 4-week follow-up. Throughout the protocol, gastrointestinal symptoms, such as abdominal pain, flatulence and bloating were recorded daily, along with weekly faecal samples. At the end of each stage of the study, questionnaires were filled out by the children’s caregivers to assess behaviour – Autism Treatment Evaluation Checklist (ATEC), The Spence Children’s Anxiety Scale subscale-P (parent-report), the Autism Spectrum Quotient (AQ) and the Empathizing Quotient/Systemizing Quotient (EQ-SQ).
The results showed a significant change in anti-sociability scores in those consuming an exclusion diet in combination with Bimuno® GOS (Grimaldi et al., 2018). These results support the hypothesis that the gut microbiome could be implicated in the pathophysiology of ASD and as such, should be of consideration in future research.
Read the full open access paper here:
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