Autism and the Microbiome: A Summary of What We Know Now

Two days ago, I spotted a short commentary[i] in the journal, International Journal of Molecular Sciences, from this past August, which really caught my attention. Here is why:  it was written by 3 researchers in the department of neurology at Rutgers University’s medical school who state that, “We will explore the potential for treatment of ASD [autism spectrum disorders] by targeting the microbiome with probiotics….this paper will attempt to provide significance to the aggregation of the research in this area of research.”  It really is a great summary of what we now know.

Here are just some of the facts the paper presents:

1. “Almost half of children with ASD suffer from at least one GI symptom…with diarrhea and constipation being the most common symptoms reported.”
2. “Additionally, recent studies show the severity of GI symptoms as being significantly correlated with the severity of autism symptoms.”
3. “The balance of microorganisms in the intestinal tract of ASD individuals has been found to differ from that of neurotypical individuals.”
4. “…the presence of autistic symptoms in children has been correlated with a less diverse gut microbiome…”
5. “The association of ASD and a number of microbial overgrowths, including various species of bacteria and Candida, have been further confirmed by independent studies over time.”
6. “Small Intestine Bacterial Overgrowth has been correlated with ASD.”

They conclude this list of findings by stating, “Taken together, all these microbiome alterations may be associated with the increased gastrointestinal disturbances in individuals with ASD.”

More than that, there are other highly significant findings in autism that point to a gut origin.  A few examples:

1. “Stool testing found lower levels of short chain fatty acids [SCFAs] in children with ASD…”
2. “Another study found increased levels of IgA [antibodies] in stool samples of children with ASD compared to healthy children, suggesting the presence of gut immune abnormalities in ASD.”
3. “…increased gut permeability or ‘leaky gut’ is implicated in ASD.”
4. “…both the intestinal barrier and brain barrier may be impaired in ASD, with decreased levels of intestinal tight junction components…”

Ok – so let’s summarize.  We know that people with autism have GI symptoms markedly more often than people without ASD, and that the severity of those symptoms correlate with the severity of their autism.  We know that they have altered gut microbiota, including SIBO, lower levels of beneficial bacteria, lower levels of anti-inflammatory SCFAs, increased frequency of leaky gut/leaky brain.  We know that “This ‘leaky gut’ theory would offer a mechanism by which GI disturbances could play a role in neurodevelopment and cognition.”

But wait…there’s more.  We know that TREATING these microbiome alterations alleviates the symptoms of autism.  Again, just a few of the findings the paper cites.

1. “Nearly two decades ago, a study found that vancomycin [a non-systemic antibiotic] temporarily improved behavior and communication in ASD.”  (I was actually there when this paper was first revealed at a conference.)
2. “Parents of children with ASD who received a specific five strain probiotics Delpro  reported a significant improvement in bowel habits and behaviors measured by autism treatment evaluation checklist.” (This surprised me as it’s a very low-potency (10 billion) product.  Might be worth a try!)
3. “Antifungal treatment also demonstrated some efficacy in vivo.”

(Just yesterday, in fact, I read about a study[ii] out of Baylor College of Medicine wherein, researchers tested probiotics in a rodent model of autism.  The researchers report that, “…administration of the bacterium Lactobacillus reuteri could lead to specific changes in the brain that reverse social deficits through a mechanism that involves the vagus nerve and the oxytocin-dopamine reward system.”  (I have written about L.reuteri and autism before in a post about these researchers’ previous paper on this subject!)  When the vagus nerve, which connects the brain to the gut (and many other parts of the body), is activated it releases oxytocin, a hormone that increases social behavior.  Lowering the level of the L.reuteri in the guts of pups reduces their social behavior.  Increasing the level restores it.  If the vagus nerve that connects the gut to the brain is cut, L.reuteri does not restore social behavior, proving that it exerts its effect through the nerve.  In mice who were genetically engineered to “…lack oxytocin receptors in the reward neurons or blocked the receptors with specific drugs, L.reuteri also could not restore social behaviors in the ASD mice.”  Thus, the scientists were able to determine the exact mechanism by which the probiotic was exerting its effect.)

Back to the commentary, in the concluding paragraphs, the researchers say, “While research into the gut-brain connection in autism still remains in its preliminary phases, there is a convincing body of evidence that suggests a relationship between gastrointestinal distress and autism….”

A week ago, two papers[iii] were published in the eminent journal, Pediatrics, which showed that 1 in 40 children born in the United States (between the ages of 3 and 17) has autism. This is literally a national catastrophe at this point. Obviously, we need way more research into the gut-brain axis in autism.  After all, as these scientists write, “…even today, it is becoming evident that the gut, specifically the disturbance of it, plays an important role in certain neurological disorders including ASD.”

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[i] Fowlie, G, Cohen, N, Ming, X. The perturbance of microbiome and gut-brain axis in autism spectrum disorders.  International Journal of Molecular Sciences. 2018;19(8): pii: E2251. doi: 10.3390/ijms19082251.

[ii] https://medicalxpress.com/news/2018-12-microbial-based-treatment-reverses-autism-spectrum.html

[iii] https://www.spectrumnews.org/news/national-surveys-estimate-u-s-autism-prevalence-1-40/