Microbes in the human gut are connected to autism, a new study has shown.
Reanalyzing existing studies, researchers identified a microbial signature that marks autistic people from neurotypical individuals.
The researchers say that the research highlights the need for further long-term studies to understand the underlying causes of autism.
Previous studies have shown that the microbiome, the collection of microbes that inhabit the human gut, has been shown to play a role in autism, but the mechanics of this link have remained confusing.
Taking a new approach to the problem, a study published today in Nature Neuroscience sheds new light on the relationship between the microbiome and autism.
This research by the Simons Foundation’s Autism Research Initiative (SFARI) involved reanalyzing dozens of previously published datasets.
Emerging Connections
The results align with a recent, long-term study of autistic individuals centring on a microbiome-focused treatment intervention.
Jamie Morton, one of the study’s corresponding authors, began this work. At the same time, a postdoctoral researcher at the Simons Foundation said: “We were able to harmonize seemingly disparate data from different studies and find a common language with which to unite them.
“We identified a microbial signature distinguishing autistic from neurotypical individuals across many studies.
“But the bigger point is that going forward, we need robust long-term studies that look at as many datasets as possible and understand how they change when there is an [therapeutic] intervention.”
With 43 authors, this study brought together leaders in computational biology, engineering, medicine, autism and the microbiome.
A new paper by 43 scientists of various disciplines found the most vital link between gut microbes, host immunity, genetic expression in the nervous system, and dietary patterns.
Gut Bacteria and Autism
The new analysis does not confirm autism’s underlying causes, nor does it identify specific subtypes as other research has attempted, but rather reveals a more generalized gut profile that seems consistent among those with ASD.
If this crucial biomarker can be elucidated in further research, it could one day be used to diagnose ASD and probe potential treatments.
“Before this, we had smoke indicating the microbiome was involved in autism, and now we have a fire,” says microbiologist Rob Knight from the University of California San Diego.
“We can apply this approach to many other areas, from depression to Parkinson’s to cancer, where we think the microbiome plays a role, but where we don’t yet know exactly what the role is.”
Implications for Diagnosis and Treatment
Today, scientists know that people with autism are more likely to experience gastrointestinal issues, such as constipation, diarrhoea, bloating, and vomiting.
In recent years, researchers have begun to find links between the makeup of microbes that call our guts home and neurodevelopmental disorders like ASD.
Nevertheless, this connection isn’t always consistent, and some experts have argued it isn’t gut bacteria that trigger ASD, necessarily; it could be that kids with autism are more likely to restrict their diets because of ‘picky’ eating, which in turn influences the kinds of bacteria that persist in the digestive tract.
The new study incorporates ten existing datasets on autism and the microbiome, plus 15 other datasets regarding dietary patterns, metabolism, immune cell profiles, and gene expression profiles of the human brain.
The authors of the analysis say their findings boost “the statistical power and biological insight” into the gut-brain axis behind ASD and provide “stronger associations among gut microbes, host immunity, brain expression and dietary patterns than previously reported”.
The fundamental connection between the gut and the brain is a relatively new scientific frontier. In 1992, a researcher named the heart “the neglected human organ”, and it took until the 21st century for the term “human microbiome” to be properly conceptualized.
In the years since research on the trillions of individual microbes found in our guts has blossomed, experts still need to figure out what to make of their results. To date, it still needs to be clarified what a healthy microbiome looks like and what an atypical one is.
Gut Bacteria and Autism Spectrum Disorder
There are many variables to consider, especially because communication between the gut and the brain seems to be a two-way street, and diet can quickly change the mix of gut bacteria.
In 1998, a scientist named ER Bolt first hypothesized abnormal gut microbiota could be involved in the development of ASD.
Those with autism, for instance, showed more species of Clostridium and Ruminococcus bacteria in their stool than in a control group.
But these early studies were generally deemed to be of “low to moderate quality, predominantly due to small sample sizes”, “inadequate or absent explanation of sources” of the stool samples, and “potential biases”, according to a trio of Dutch nutrition researchers reviewing the evidence in 2014.
Even today, carefully designed, long-term studies take a lot of work, and there needs to be more agreement from paper to paper.
The current analysis attempts to bridge that gap by comparing existing data on the gut and ASD. The research team designed an algorithm for each dataset to match the best pairs of autistic and neurotypical individuals by age and sex, two common confounding factors in autism studies.
Rather than analyzing
