What Is The Autism-gut Connection?

by Kristina C. - May 16, 2016

Science writer , from Victoria, BC, is a freelancer whose work has appeared in publications throughout North America and Europe. She currently worked as a web editor for the Gut Microbiota for Canada pharmacy on line.

fecal microbiota transplant FMT

John Rodakis, the parent of a child with autism, says he observed something remarkable in 2012. After his son began a course of a common antibiotic (amoxicillin) for a strep infection, some of the autistic behaviors suddenly began to improve. Rodakis says after four days on the antibiotics, his son began making eye contact, speaking more clearly, and showing more energy; he even rode a tricycle around the room for the very first time.

Parents of children with autism may have heard similar things talked about in waiting rooms or on playgrounds: dramatic improvements in behavior with a certain gut-focused medication or intervention. The problem is, these kinds of observations don’t fit into our current understanding of autism.

Autism spectrum disorder (ASD) is a neurodevelopmental condition, diagnosed through behavior alone. There are no lab tests to tell whether a person falls on the autism spectrum. For diagnosis, a child must show both deficits in social communication and interaction, and restricted or repetitive behavioral patterns. Genetic predisposition plays a big role in ASDs. But anyone who claims that symptoms have improved because of a biological intervention like antibiotics is going out on a limb.

Yet science moves forward one careful observation at a time. So if we take the report of Rodakis at face value, what might it mean?

The first possibility is that some of the behaviors parents chalk up to autism are not actually due to autism—rather, they are the result of coexisting gastrointestinal (GI) problems. Let's say a child refuses to ride a tricycle, preferring instead to lie on the floor. It's possible that, all along, the child had gastrointestinal pain and bloating that made the act of pedalling a bicycle uncomfortable. The willingness of the child to ride a tricycle after receiving antibiotics could be because the GI symptoms have been alleviated.

But another possibility that incorporates the Rodakis observation would require changes to the way we think of autism—that some of the behaviors in the disorder can be altered just by changing biological function in the gastrointestinal tract. What if the antibiotics suppressed the activity of certain gut bacteria that were affecting behaviors through the gut-brain axis? If this turned out to be true, we'd have to allow a role for something other than just genetics in shaping the behaviors of a person with autism. We’d have to open the door to the idea that interventions targeting the gut could shape what a child does.

Here's what we do know about autism and the gut: individuals with autism more frequently suffer from gastrointestinal problems, and seem to have a distinctive set of gut bacteria from neurotypical children. These are just correlations, though, so they don’t necessarily mean autistic behaviors can be changed by targeting the gastrointestinal tract.

In mice, however, there’s a hint that the behaviors of autism can indeed be manipulated through gut bacteria. Researchers at Caltech activated the immune systems of pregnant mice, and the offspring turned out to have a mouse version of autism. The mouse pups showed increased repetitive burying of marbles, reduced vocalizations in response to a social encounter, and other autistic-like behaviors. Remarkably, giving these young mice a human-derived bacteria called Bacteroides fragilis corrected many of these behaviors, making the mice look more typical. This work does support the notion that manipulating the gut microbiota could improve some of the behaviors of autism, but there's a lot more work to do before we know whether this applies to humans.

You don’t have to look very far to find purported treatments for autism that target the gut: fermented food diets, probiotics, and even fecal microbiota transplantation. But the truth is, the scientific reports of these interventions successfully improving behaviors are currently few and far between. Genetic risk is still the best explanation of why children end up with ASDs, and those who say they can help children with autism by manipulating gut bacteria are not supported by adequate science.

Detailed knowledge about human autism and gut bacteria will require large and expensive studies. But with the incidence of ASDs growing—now 1 in 68, according to recent estimates—and with the profound ways the disorder can impact families, it’s a line of research that deserves urgent attention.


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