Children with autism spectrum disorder (ASD) appear to have a distinctive and underdeveloped range and volume of gut bacteria, known as the microbiome, that is not linked to their diet, a small study by researchers at The Chinese University of Hong Kong have found and published online in the journal Gut.
Seeing how the incidence of ASD has increased dramatically over the past two decades, and how many children with ASD continue to have difficulty with language or social skills for the rest of their lives, motivated the team to research the impact and role gut microbiota has in ASD in children.
The gut-ASD axis
In the study, the researchers sought to understand if children with autism between the ages of three-six might have a microbiome that differs significantly from that of TD children, which, once understood, might be used to facilitate early treatment.
The team compared the range, volume, and associated functions of bacteria in the stool samples of 128 Chinese children, 64 with an ASD diagnosis and 64 without. Differences were further confirmed in a separate group of 18 children, eight with autism and 10 without.
“Currently, diagnosis is mostly based on physician assessment and subjects may have to wait a long time to see behavioural therapists or psychiatrists for diagnosis,” shares Professor Siew Ng, Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong, China. “Given that there are no non-invasive tools or biomarkers relevant to ASD available, we believe identifying non-invasive microbial biomarkers can pave the way for early detection especially in suspected cases.”
The gut microbiota also plays a more important role in other neurodevelopmental disorders such as ADHD.
Neurotransmitter activities and bacteria markers
The study showed that gut microbiome alterations in children with ASD were not associated with diet. “We demonstrated for the first time persistent under-development of gut microbiome in children with ASD compared to their age- and gender-matched TD children,” highlights Ng.
Bacteria associated with neurotransmitter activities were substantially lower in children with ASD. The team also identiﬁed five bacteria markers that differentiate children with ASD from TD children in a discovery cohort and validated the findings in an independent cohort.
“By using these five markers, we were able to develop a prediction algorithm for detection and prediction with 80 per cent sensitivity,” outlines Ng.
The researchers believe there is the potential for the use of stool samples as non-invasive screening for ASD in the future.
The research team, found that Clostridium, Dialister and Coprobacillus were enriched in children with autism while Faecalibacterium was significantly decreased. Several Clostridium species enriched in children with autism closely interacted with each other and formed a connected group.
Clostridia species have been linked with autism via the production of clostridial toxins which can damage the central nervous system. “So the finding here may lead to discovery and targeting of pathogens that connect the brain and gut leading to these symptoms,” notes Ng.
Links with diet and nutrition
Current understanding suggests children with ASD typically have different eating behaviours or habits which might influence the gut microbiota.
“However, in our study, the factors most strongly and independently associated with microbiome composition in the stool samples were age, autism, and weight (BMI)—and diet wasn’t an influential factor,” stresses Ng. “The data suggests that the abnormal gut microbiota seen in ASD is unlikely to be the effect of differences in diet and represent real pathological abnormalities that warrant further investigations for therapeutic targets,” Ng continues.
”Future therapeutics targeting reconstitution of gut microbiota in early life and increasing abundance of neurotransmitter-synthesised bacteria such as Faecalibacterium should also be explored for ASD.”
As this is a study based on the Chinese population and the gut microbiome can vary according to geographical region, Ng highlights: “The associations between gut microbiota development and ASD development should be investigated in other regions and populations.” In addition, apart from bacteria markers, she states that “targeted bacteria metabolites should also be considered in future ASD treatment”.
Wan Y, Zuo T, Xu Z, et al
"Underdevelopment of the gut microbiota and bacteria species as non-invasive markers of prediction in children with autism spectrum disorder"