What’s the link between autism and gut bacteria?

No matter how lonely you might feel, rest assured you’re never by yourself. Millions of microorganisms live in relative peace and harmony inside our guts, collectively comprising the “gut microbiota”. More and more research suggests that abnormalities in this microbiota can impact virtually all organs — and that includes the brain, too. And, according to a new study, treating the gut’s microflora could be key to easing autism symptoms.

Credit: Pixabay.

The connection between the gut microbiome and the brain is known as the microbiome–gut–brain axis. This connection is of important interest to researchers because individuals suffering from neurological and developmental conditions, such as Alzheimer’s disease and Autism Spectrum Disorders, also suffer from chronic gastrointestinal symptoms.  One 2014 study published in the journal Pediatrics, for instance, found that children with autism are about four times more likely to experience gastrointestinal (GI) distress than are their typically developing peers.

If abnormal gut bacteria may be amplifying autism symptoms, would a healthy microbiome improve symptoms? In a recent study, researchers at Arizona State University and Northern Arizona University attempted to answer this question.

For their study, they recruited 18 children with Autism Spectrum Disorder who also had chronic gastrointestinal problems. The participants followed a 10-week treatment consisting of antibiotics, a bowel cleanse, and then a high dose of microbiota fecal transfer (MTT).

According to the results, eight weeks after the treatment, 80% of the patients experienced reductions in gastrointestinal symptoms and slow, but significant improvements in their autism-related symptoms.

Two years later, the patients still experienced a 58% improvement in gastrointestinal symptoms as measured by the Gastrointestinal Symptom Rating Scale. Some of the symptoms that showed improvement include abdominal pain, indigestion, diarrhea, and constipation.

These results could be considered quite spectacular seeing how all of the patients claimed they hadn’t had normal gastrointestinal tract functioning since infancy. Meanwhile, the severity of autism symptoms dropped by 47%. At the beginning of the study, 83% of the children were classified as “severe” on the autism spectrum. However, two years post-treatment, only 17% of children fell under this classification. Most shocking of all, 44% of the participants had scores below the Autism Spectrum Disorder diagnostic cut-off point, the authors wrote in the journal Scientific Reports.

“Important changes in gut microbiota at the end of treatment remained at follow-up, including significant increases in bacterial diversity and relative abundances of Bifidobacteria and Prevotella. Our observations demonstrate the long-term safety and efficacy of MTT as a potential therapy to treat children with ASD who have GI problems, and warrant a double-blind, placebo-controlled trial in the future,” the authors wrote.

Another study published this month by a team led by Dr. Katerina Johnson of Oxford University’s Department of Experimental Psychology found that both gut microbiome composition and diversity were related to differences in personality, including sociability and neuroticism.

“This suggests that the gut microbiome may contribute not only to the extreme behavioural traits seen in autism but also to variation in social behaviour in the general population. However, since this is a cross-sectional study, future research may benefit from directly investigating the potential effect these bacteria may have on behaviour, which may help inform the development of new therapies for autism and depression,” Johnson said.

It’s not clear what could drive this association but having different populations of digestive tract bacteria and patterns of gene expression have been previously identified as potential factors.

There are still a lot of unanswered questions considering the field is still in its infancy, yet growing rapidly. Just the idea that microbes could influence the brain was unthinkable a few years ago and the pace of research has accelerated over the past few years. Just imagine the possibilities: in the future, it could be possible that ASD symptoms are remedied with bacterial metabolites; there might even be probiotics for autism.

More research is warranted in order to tease out the connection between gut bacteria and autism/behavioral changes. Studies so far on the subject have been mostly small and uncontrolled — and it’s not clear what they mean, given that researchers are still trying to establish the ingredients of a healthy microbiome. This, hopefully, will change in the future as more interest and funding is awarded to investigate this association that cannot be ignored any longer.

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