Can bacteria, or lack of them, in the gut predict behavioral and gastrointestinal symptoms in people with autism? New research presented in May 2019 at the International Society for Autism Research Annual Meeting in Montreal suggests that the microbiome (the collection of bacteria, viruses, and other microbes) that lives in the gut may be linked to the symptoms any one individual with autism experiences, and may provide an opportunity to therefore improve treatment of those symptoms.
“We found clear differences in the microbiota of children with autism when compared with typically developing peers of the same age,” says Ruth Ann Luna, PhD, assistant professor at Baylor College of Medicine in Houston and lead author of the study.
“This is the baseline study that we’ve all been hoping for,” she says. “We’re going to be able to answer a lot more questions with this data set that’s now in existence.”
What Is the Microbiome?
We know there are bacteria both on our skin and in our gut, as well as viruses and other microbes (germs) that cohabit with us, says Charis Eng, MD, PhD, chair of the Cleveland Clinic Genomic Medicine Institute in Ohio, who was not involved in the new research. They all make up the different microbiota of the body.
There’s a symbiotic relationship between human cells, bacterial cells, viral cells, and other microbial cells, meaning they all depend on one another to survive — and they all have to be in happy harmony for health, Dr. Eng explains. “I like to think of the microbiome as anything is that is living that is not human, inside and on our bodies.”
When this harmony is disrupted it seems to be associated with various health problems — or possibly the imbalance could predispose people to those symptoms. The new research would suggest that certain disruptions to the balance of the gut microbiome is linked to various gastrointestinal (GI) and other behavioral symptoms of autism, Eng says.
Previous studies have suggested that the gut microbiota of people with autism tend to look different compared with those of people without autism, Eng says.
Significant differences in gut microbiota have been identified, for example, in people with autism with functional GI disorders, Eng explains. This finding has been reported in a 2015 study published in the journal PLOS ONE, among others. And treatment addressing these microbiota differences (fecal transplants) actually appears to help with the symptoms, according to one study published in April 2019 in the journal Scientific Reports.
But this new research suggests that the gut microbiota of people with autism may look more different than was previously thought — and that the differences may be linked to other autism symptoms too.
Study Shows Patterns in Gut Bacteria Linked to Different Autism Symptoms
The new study from Dr. Luna and her colleagues looked at a total of 412 children — 145 kids with autism spectrum disorders, 48 siblings without autism (some with digestive problems), and 219 typically developing children. Participants were between ages 2 and 17, and the autism group represented kids across the spectrum, with symptoms ranging from mild to severe.
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Researchers gathered extensive medical histories for the individuals, as well as data from several behavioral surveys (ones that measure the presence and severity of behavioral symptoms linked to autism, like light sensitivity and repetitive behaviors). Each child also kept a two-week diary, which tracked diet, stool patterns (including form and frequency), and GI pain.
Stool specimens were collected from all the children to determine the functional GI disorders across all three groups. Researchers also used the samples to analyze patterns for the microbiota and mycobiota (the collection of fungal cells that live in and on us) of the children. From those samples, the researchers were able to identify the gut microbiome composition (meaning the unique combination of bacteria, fungi, and other organisms) for each participant.
The data revealed there are distinct differences in the gut microbiome and overall environment in the gut of children with autism compared with the other groups, and there’s not a single microbiome profile everyone with autism appears to have, says Luna.
“There are differences even within that cohort of autistic children that varies based on their GI symptoms, behavior symptoms, and even their dietary preferences,” she says. “There’s not one particular bacteria — either the absence or presence of a certain bacteria — that’s driving the separation between that autistic group and the typically developing group. It’s really much more dynamic.”
What Comes Next for Autism Microbiome Research?
If reharmonizing the gut microbiota of people with autism with GI problems helped with those symptoms (as the 2019 Scientific Reports paper found), the next question (bearing these new findings in mind) is whether or not restoring the balance of the microbiota of other people with autism with other symptoms might also help with those problems too, Eng says. And those are the questions future research will need to address.
Will stool transplants be necessary for everyone? If not, could researchers determine microbially mediated therapeutic interventions for people to counteract what is happening in the gut?
“Precision probiotics” could be another avenue to explore, Eng adds. It may be useful to look at each child’s stool composition to see what is missing and what is out of balance, she says. “Then we could specifically formulate those bacteria and then give it back to the child — as opposed to saying, ‘Let’s give the child a general probiotic,’” she says, which she adds is not likely to be effective given it may not address the needs of that individual’s gut microbiome.
This research suggested it also might one day be possible to diagnose autism based on an individual’s gut microbiome composition (which would require just a few stool samples) — and from that information you might also be able to predict what types of symptoms that individual might expect to have, Eng says. However, that would require a lot of additional research and evidence from multinational or multi-institutional studies, she adds, explaining that the research will be complex because of the complexity of autism itself.
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We know that there’s no one single gut microbiome intervention that’s going to work for everyone with autism, Luna adds. Successful intervention will likely need to happen on a much more individualized level, she says. “We’re working to try to triage which people may benefit from which therapies,” she says. “So, stay tuned.”