Autism: link between severity of the disorder and changes in the gut microbiota?

Gut dysbiosis and gastrointestinal disorders are frequently observed in children with ASD. There is also growing evidence that the gut microbiota plays a role in modulating brain signaling, an association commonly known as the gut-brain axis. Despite this, research on the relationship between gut microbiome composition and ASD has produced inconsistent results, highlighting the complexity of the disorder and the need for more sophisticated experimental designs. With this goal in mind, a US research team:

• compared the gut microbiota composition of young ASD patients to that of controls in Arizona and Colorado in order to understand whether geographic location can influence the gut microbiome.
• conducted a longitudinal study (sidenote: Subjects in Arizona were not included in the longitudinal study )  to evaluate the relationship between gut microbiota composition, ASD behavioral severity, diet, and gastrointestinal symptoms of the disorder.

Impact of geographical location on the microbiota

The researchers showed that gut microbiota composition differed between the individuals in Arizona and those in Colorado, with the Arizona children showing greater microbial diversity than the Colorado children. This came as a surprise to the researchers, who used the same stool collection and DNA extraction and sequencing methods at both locations. A further cross-analysis of a subset of DNA samples taken in both Colorado and Arizona confirmed that the DNA extraction site had no influence on microbial diversity. The researchers also showed that ASD patients had more gastrointestinal symptoms than controls in Arizona, but not in Colorado. For the researchers, this confirms the impact of the study site on the gut microbiota composition and suggests that these variations in ASD-related gastrointestinal symptoms between sites may contribute to inconsistent results in the literature.

Correlation between deteriorated speech and microbiota diversity

The longitudinal analysis revealed an association between increased severity of ASD behavioral symptoms and changes in the gut microbiota. In particular, a decrease in gut microbial diversity over time was linked to increased severity of ASD behavioral symptoms such as deteriorated speech, lethargy, or social withdrawal. On the other hand, the authors did not find any significant relationships between ASD-associated behavioral disorders and gastrointestinal symptoms or diet. For the authors, additional multicenter and longitudinal studies with more participants are required to characterize the relationship between ASD and the gut microbiota.