The connection between autism spectrum disorder (ASD) and the body’s “second brain” is clearer than ever.
A new paper written by no fewer than 43 scientists across disciplines finds the strongest link between gut microbes, host immunity, gene expression in the nervous system and diet.
The new analysis does not confirm underlying causes of autism or identify specific subtypes, as other studies have attempted, but it does show a more general gut profile that appears to be robust among people with autism.
If this crucial biomarker can be elucidated through further research, it could one day be used to diagnose ASD and explore potential treatments.
“We used to have smoke suggesting the microbiome is linked to autism, now we have fire,” says UC San Diego microbiologist Rob Knight. “We could apply this approach to many other areas, from depression to illness.” Parkinson’s and cancer.” We think the microbiome plays a role, but we don’t know exactly what that role is yet.”
Scientists know that people with autism are more likely to experience digestive problems such as constipation, diarrhea, bloating and vomiting. Moreover, in recent years, researchers have begun to find links between the microbiota and neurodevelopmental disorders such as ASD.
However, this link is not always consistent, and some experts argue that gut bacteria do not necessarily cause autism spectrum disorder; Children with autism may be more likely to restrict their diet due to “pickiness” in food, which in turn affects the types of bacteria in their digestive tract.
The new study brings together 10 existing datasets on autism and the microbiome, as well as 15 other datasets related to diet, metabolism, immune cell profiles, and gene expression profiles in the human brain.
The authors of the analysis say their findings improve “statistical strength and biological information” about the gut-brain axis underlying ASD and provide “a stronger link between gut microbes, host immunity, brain expression, and nutritional patterns than previously reported.”
And the fundamental relationship between the gut and the brain itself is a relatively new frontier in science. In 1992, a researcher called the gut an “abandoned human organ” and it wasn’t until the 21st century that the term “human microbiome” was properly understood.
Since then, research has blossomed into the trillions of individual microbes in our gut, but experts are still unsure what to make of their findings. It is still unclear what a healthy microbiome looks like, let alone an unusual microbiome.
And there are many variables to consider, especially because the gut-brain connection seems like a two-way street, and because diet can quickly change the composition of gut bacteria.
In 1998, a scientist named E. R. Bolt hypothesized that abnormal gut microbes might be involved in the development of ASD.
For example, more Clostridium species and rheumatoid bacteria were found in stools in people with autism than in controls.
But these early studies were generally considered to be of “low to moderate quality, mainly due to small sample sizes” and “inadequate or missing interpretation of stool sample sources and potential biases,” according to three Dutch nutrition experts.
Even today, well-designed long-term studies are difficult to find.
The current analysis attempts to fill this gap by comparing existing gut and ASD data. For each data set, the research team developed an algorithm to best match pairs of people with autism and neurotype by age and gender, two common factors that influence autism research.
Instead of analyzing study averages, each of the 600 pairs was treated as a single data point, allowing researchers to simultaneously analyze gut microbiome differences across more than 1,000 individuals.
Finally, the researchers found key markers of autism in certain metabolic pathways associated with diet, gene expression, and specific gut microbes.
What’s more, these microbiomes were consistent with those found in a recent long-term study of stool transplants in 18 autistic children. After two years, participants showed sustained improvement in gastrointestinal and behavioral symptoms, based on the scale most commonly used to assess autism spectrum disorder symptoms.
Taken together, the results point to a possible role for the microbiome in improving autism symptoms, although it remains unclear how these underlying gut changes are related to actual brain changes.
Jamie Morton, who served as a biostatistician for the Simons Foundation, a charity that funds biomedical research, explains: “We were able to reconcile seemingly disparate data from different studies and find common ground to bring them together. Because of this, we have been able to “Identify the microbial fingerprint that distinguishes autistic people from neurotypical people in many studies. But more importantly, going forward, we need robust long-term studies that look at as many datasets as possible and change when there is a treatment intervention.”
The study is published in the journal Nature Neuroscience.
Source: Science Alert
