Gut Microbiome May Offer Novel Bacterial Markers in Kids With Autism

By Lisa Rapaport

July 30, 2021

(Reuters Health) - Children with autism spectrum disorder may have a distinctive and underdeveloped gut microbiome that isn't related to their eating habits, a small Chinese study suggests.

Researchers performed deep metagenomic sequencing of fecal samples collected from 64 preschoolers aged 3-6 with autism spectrum disorder (ASD) and 64 age-matched typically developing children. They also compared gut microbial composition and functions between the two groups.

The analysis identified five bacteria in children with autism that weren't found in children without the condition: Alistipes indistinctus; candidate division_TM7_ isolate_TM7c (single cell organism); Streptococcus cristatus; Eubacterium limosum; and Streptococcus oligofermentans.

Children with ASD also had significantly fewer bacteria linked to neurotransmitter biosynthesis than their typically developing counterparts.

In addition, researchers identified 26 age-related bacterial species as proxies of typical development of the gut microbiome by age, and found these were present in typically developing children but not in ASD children of the same age.

"The gut microbiota of children with ASD is abnormally developed and lags that of age-matched peers," said senior study author Dr. Siew Ng of the Center for Gut Microbiota Research at the Chinese University of Hong Kong.

"These data support the potential role of non-invasive prediction of ASD based on fecal bacteria markers and age-related bacteria development profile," Dr. Ng said by email. "Currently, diagnosing autism spectrum disorder can be difficult, because there is no definitive medical test and diagnosis is based on physician assessment."

The factors most strongly and independently associated with microbiome composition in the stool samples were age, autism, and BMI, researchers report in Gut. Diet, however, didn't appear to significantly influence microbiome composition differences between children with and without ASD.

Children with ASD had stool samples with a greater variety of microbes than age- and weight-matched children without ASD.

Clostridium, Dialister and Coprobacillus were enriched in children with autism. Researchers also found that clostridium species enriched in children with autism closely interacted with each other and formed a "connected group."

Clostridia species have been previously been linked with autism via the production of clostridial toxins which can damage the central nervous system, the study team notes.

One limitation of the study is its small size. Another is that the gut microbiome can vary regionally, and it's possible results from this small group of Chinese youth may not be generalizable to other populations.

However, it is not surprising that ASD might have underdevelopment of the gut microbiota that is unrelated to diet, said Xingyin Liu, pathogen biology-microbiology and autism researcher at Nanjing Medical University in China who wasn't involved in the study.

Previous research suggests that host genetics factors in ASD partially contribute the characteristics of gut microbiota in ASD, Liu said by email.

"ASD is a complex disease with very strong heterogeneity, so development of microbiota-based therapeutic intervention is still a way off," Liu said. "Given this heterogeneity, research into gut microbiota in different subtype ASD using a larger cohort may help doctors to apply microbiome-based stratification and therapy of ASD patients."

SOURCE: Gut, online July 26, 2021.