The Unlikely Connection Between the Gut and ASD

Sources:

• https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-brain-gut-connection 

• https://hms.harvard.edu/news/gut-brain-connection-autism 

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9355470/ 

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5005185/ 

• https://www.science.org/doi/10.1126/science.aad0314 

If you or someone you know has Autism Spectrum Disorder (ASD), then it wouldn’t be unlikely that whoever has ASD also experiences gastrointestinal issues. Inflammatory bowel disease, diarrhea, and constipation all have been observed to strangely occur in people with ASD. But what’s the reason behind this seemingly random link between a neurological disorder and gastrointestinal issues?

The connection might not be as random as you think. In fact, it stems from human anatomy. Within the walls of every human being’s gut are millions of nerve cells that make up the enteric nervous system (ENS). While its main job is to regulate digestion of foods along the digestive system, the ENS has also been described by scientists as a “second brain.” It's described as such partly because of its connection to the central nervous system (CNS), mainly through an outstretching ‘wire’ between the two systems called the vagus nerves. 

Additionally, the CNS and ENS share many common neurotransmitters, signaling pathways, and hormones, making one susceptible when the other changes. One common possible example of the connection between the ENS and CNS is the feeling of butterflies in your stomach when you’re nervous. Plus, researchers have found evidence that gastrointestinal issues can influence changes in the mood of an individual. However, keep in mind that the link between the gut and the brain is complex and still largely unexplored, meaning new information could surface at any point in time that changes how we view this connection. 

Now that the link between the brain and the gut has been established, what does this have to do with ASD? Research by Harvard Medical School and MIT researchers have found one potential link between infection during pregnancy and both autism-like phenotypes in offspring and experiencing inflammatory problems later in life. They were able to draw conclusions on the link between the two outcomes to the inflammatory signaling molecule interleukin-17a (IL-17a), where IL-17a acting on the fetal brain of mice can induce “autism-like behavioral phenotypes” (Choi et al., 2016) and pups that exhibited intestinal inflammation from mothers with stool from maternal immune activation (MIA) could produce increased IL-17a. Basically, a connection could be made between a common signaling molecule that can lead to both ASD and intestinal inflammation developing. It’s important to note, however, that these experiments were only performed on mice, meaning this isn’t concrete, but hopeful, evidence of this same link occurring in humans.

Another fascinating link between ASD and gastrointestinal issues can be found in the fact that the bacteria Clostridium boltae in the gut can lead to the development of gastrointestinal issues, and Clostridium bacteria in the colon has been shown to indicate higher risk and severity of ASD. 

Although currently there is no concrete connection between ASD and the abnormal gastrointestinal issues those with the disorder may experience, compelling research serves to help find more pieces to help solve this odd bond. And a stronger link established, more effort can be made to better accommodate those with ASD’s needs.