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Gut-brain axis insights: why the microbiota holds therapeutic potential for neuro-developmental disorders

Evidence is emerging that there are important connections between the gut microbiome and neurodevelopmental disorders. In a guest post for World Autism Awareness Month this April, Chris Kenji Beer reviews recent discoveries.

In recent years, scientists from all over the world have made great strides in linking the health of our gut microbiome to autism. Scientists are getting very close to finding microbial solutions to autism and have already discovered immune support remedies that reduce symptoms.

Autism and the gut microbiome

It is known among professionals in the field that people with autism are more likely to experience gastrointestinal disorders than the general population. One review found that children with autism (ASD) were four times more likely to have gastrointestinal issues than children without autism.[1]

The findings of a collaboration between three Australian universities exploring the connection between the gut and autism were published last month in The Conversation.[2] Their research studied mice and human twins with autism. It showed a gene mutation called neuroligin-3 and a connection to deficiencies of certain strains of gut bacteria.

Serotonin production an influencing factor

Which specific strains differ among autistic people from the general population? The production of serotonin appears to be a contributing factor to ASD.

A recent article in Nature references a University of Arizona study on microbiota transfer therapy, which is used to recolonize the guts with bacteria of children suffering from autism. Children with autism often have a distinctive gut microbiome with a deficiency of specific gut microbes. These include Bifidobacterium, Blautia (needed to produce bile acids which in turn produce serotonin), Veillonellaceae, Coprococcus, and Prevotella. Conversely, researchers found an excess of the Clostridia bacterial pathogens (known to disrupt production of serotonin in the gut).[3]

Gut microbiome’s influence on social behavior

John Cryan, a biochemist at University College Cork in Ireland, was among the first researchers to investigate how gut microbes affect social behaviour.[4] His research suggests a connection between our gut microbiome and autism. In 2014, Dr. Cryan found that germ-free mice — those lacking the typical mix of gut microbes — avoided other mice, shunned new social situations, and groomed themselves excessively. “It started to crystallize that the microbiome was involved in many aspects of behaviour,” Cryan says.

The prevalence of Clostridia bacterial pathogens, for instance, generate propionic acid in the gut — a short-chain fatty acid known to disrupt the production of neurotransmitters. Propionic acid also causes autism-like symptoms in rats.

Deficits in beneficial gut bacteria might also affect social brain function.

In 2017, Dr. Cryan found that when mice with an autism-like condition had lower levels of Bifidobacterium and Blautia gut bacteria, their guts made less tryptophan and bile acid — compounds needed to produce serotonin. Children with autism have been consistently found to have lower levels of Veillonellaceae, Coprococcus and Prevotella gut bacteria.[5]

Maternal influences on autism

In early 2019 MIT and the University of Massachusetts Medical School found similar impacts of identifiable microbial strains.

Researchers found that the gut microbiome composition of the mother’s gut can influence whether maternal infection leads to autistic-like behaviours in offspring. They also discovered the specific brain changes that produce these behaviours. 

The same MIT report referenced a 2010 study where all children born in Denmark between 1980 and 2005 with severe viral infections during the first trimester of their mother’s pregnancy led to risk for autism by three times. Studies show that children with Autism Spectrum Disorder (ASD) often have a mix of gut microbes that substantially differ from children without ASD.

In a 2016 paper, Drs. Gloria Choi and her husband Jun Huh found that types of immune cells known as Th17 cells, and their effector molecule, called IL-17, are responsible for this effect in mice. IL-17 then interacts with receptors found on brain cells in the developing fetus, leading to irregularities that the researchers call “patches” in certain parts of the cortex known as the somatosensory cortex. 

The big picture

Our gut microbiome is being researched about its influence on everything from autism, multiple sclerosis, PTSD, Parkinson’s Disease and brain health to cancer, depression, obesity, diabetes and weight loss. 

An article in The Guardian, “Gut bacteria regulate nerve fibre insulation” claimed that “alterations in our gut bacteria composition may be connected to a wide range of neurological and psychiatric conditions, including autism, chronic pain, depression, and Parkinson’s Disease.”

Psychosomatic Medicine reported that “various factors play a role (in PTSD), including a lack of social support and low levels of the neurotransmitter neuropeptide Y.[6]

So the social factor and gut microbiome influences are not limited to autism.

While remedies for treating mental health issues such as autism are not conclusive and not yet FDA approved, these studies offer compelling insights into the influence of our gut microbiome on mental health issues such as autism.

A safe and effective microbial influencing solution might be just around the corner. For now, it is a good idea to focus on the food you eat, including a rich diversity of prebiotic and probiotic foods and herbs. Parents of autistic children have long claimed that giving their autistic children a healthy probiotic diet has helped reduce their autistic behaviors. 

Chris Kenji Beer is an experienced health writer and editor. He is editor and writer of the Herbsprout.com blog and podcast. Email Chris with your questions or comments at [email protected]

The 7th Microbiome and Probiotics R&D and Business Collaboration Forum will bring together 400+ leaders in industry, research and business to discuss cutting-edge research and commercialisation strategies. Find out more here.


References

1 – Barbara O. McElhanon, Courtney McCracken, Saul Karpen and William G. Sharp (2014), ‘Gastrointestinal Symptoms in Autism Spectrum Disorder: A Meta-analysis’, Pediatrics, Vol. 133 no. 5, pp 872-883. (Available at https://pediatrics.aappublications.org/content/133/5/872)

2 – Elisa Hill-Yardin, Ashley Franks and Sonja McKeown, ‘Science continues to suggest a link between autism and the gut. Here’s why that’s important’, The Conversation,10 March 2020. (Available at https://theconversation.com/science-continues-to-suggest-a-link-between-autism-and-the-gut-heres-why-thats-important-118914)

3 – Elizabeth Svoboda, ‘Could the gut microbiome be linked to autism?’, Nature Outlook, 29 January 2020. (Available at https://www.nature.com/articles/d41586-020-00198-y)

4 – Ibid.

5 – Ibid.

6 – Emma Young, ‘The bacteria in your gut might affect your vulnerability to PTSD’, The British Psychological Society Research Digest, 22 November 2017. (Available at https://digest.bps.org.uk/2017/11/22/the-bacteria-in-your-gut-might-affect-your-vulnerability-to-ptsd/)

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