What Role the Brain and Gut have in Autism Spectrum Disorder

By Sarah Johnson

Autism Spectrum Disorder is a developmental disability that causes challenges in socializing, behavior, and communication. Autism Spectrum Disorder (ASD) currently has no cause or cure however, researchers are working hard to change that.

In a previous article from us, we discussed the association between gut microbiome and autism. To summarize, researchers have found that many children with ASD have gut problems and food allergies. These gut problems are caused by food not being able to completely digest (mostly protein), which creates natural opioids¹. It has been suggested that if digestion is incomplete, it will result in short chains of amino acids or peptides, and opioid by-products of these dietary proteins will enter the blood through a “leaky gut” ².

In simpler words, our stomachs have an extensive intestinal lining covering more than 4,000 square feet of surface area³. When the lining is working properly, it forms a compacted barrier that filters what can and can’t get absorbed into our bloodstream. When this lining has large cracks or holes (peptides), it can’t properly filter what gets into the bloodstream, essentially “leaking” partially digested food and toxins beyond the lining (opioid by-products). This process results in what we call a “leaky gut”.

The YouTube video by Dr. Emeran Mayer called Could Autism Be Caused by Gut Microbes?, greatly explains the way the gut works in relation to the brain. In this video he discussed research on mice that might reflect some key findings to autism.

The research he talked about is titled, Human Gut Microbiota from Autism Spectrum Disorder Promote Behavioral Symptoms in Mice which was conducted in 2019 and last modified in 2020 ⁴. As you can see, this is very recent research which means there is a lot more to be added to the story.

The study seeks to uncover if people with ASD were more likely to have issues with gut microbiome because it was a cause of ASD or if it was just a symptom of ASD. The suggestion is cause and effect, meaning is if the gut microbiome is a symptom or a cause. In order to do so, they used mice that were “germ-free”, which are mice that are grown in the lab with no microorganisms. They took the germ-free mice and transferred gut microorganisms from human children with autism into one group and then transferred gut microorganisms from human children without autism into the other group of mice.

They observed that the mice with the microorganism transfer from children with ASD exhibited behaviors similar to those with ASD, while the transfer in mice with the typically-developing individuals did not show those symptoms. The symptoms included less time interacting with other mice, vocalized less, and the mice inhibited repetitive behaviors. These symptoms can be compared to symptoms of individuals who have autism spectrum disorder.

The mice with microbiota from individuals with ASD exhibited autism-like behaviors, whereas the mice harboring microbiota from typically-developing individuals did not show these symptoms. Specifically, they spent less time socially interacting with other mice, vocalized less, and exhibited repetitive behaviors. These symptoms are analogous to behavioral characteristics of people with ASD.

In addition to the behavioral changes of the mice with the microorganism transfer from individuals with ASD, the researchers also found changes in the brain. They found that the gene expression in their brains were altered and changes in the type of metabolites present. Cancer.gov describes a metabolite as, “A substance made or used when the body breaks down food, drugs or chemicals, or its own tissue (for example, fat or muscle tissue)” (2021). Two of the metabolites they found in the mice were 5-aminovaleric acid (5AV) and taurine, found in low amounts. Both of these metabolites affect neural receptors called GABA receptors. The effect of these imbalances of metabolites on behavior have a similar relationship to the behavioral challenges individuals with ASD face.

After those findings, the research team decided to test on BTBR mice, which are a strain of mice that are most noted for their similarities to humans on the autism spectrum. They gave the BTBR mice doses of 5AV and taurine to test if the increase of metabolites would decrease the behavioral symptoms. They found that when the BTBR mice were treated with 5AV and turine they did indeed show a decrease in autism-like behavior.

Relating back to what Dr. Emeran Mayer said in his youtube video linked above, these findings are much more complex when being applied to humans. The results simply give a lead-way into what role gut-health holds for those who have ASD. Since this study is very recent, there is a lot more for researchers to discover and bounce off-of. These results are exciting and the future of what we know about ASD is looking bright.

To learn more about children with autism spectrum disorder, we have provided more blogs on our website for you to read. Snactripster is an advocate for those with ASD, and we hope to spread awareness of ASD to many.

¹ Levy SE, Hyman SL. Complementary and alternative medicine treatments for children with autism spectrum disorders. Child Adolesc Psychiatr Clin N Am. 2015 Jan;24(1):117-43. doi: 10.1016/j.chc.2014.09.004. Epub 2014 Oct 3. PMID: 25455579.

² Whiteley, P., Shattock, P., Knivsberg, A. M., Seim, A., Reichelt, K. L., Todd, L., Carr, K., & Hooper, M. (2013). Gluten- and casein-free dietary intervention for autism spectrum conditions. Frontiers in human neuroscience, 6, 344. https://doi.org/10.3389/fnhum.2012.00344.

³ Odenwald, M., Turner, J. The intestinal epithelial barrier: a therapeutic target?. Nat Rev Gastroenterol Hepatol 14, 9–21 (2017). https://doi.org/10.1038/nrgastro.2016.169.

⁴ Sharon, Gil, et al. "Human gut microbiota from autism spectrum disorder promote behavioral symptoms in mice." Cell 177.6 (2019): 1600-1618.