A new study has unveiled a promising, cost-effective method for diagnosing autism, raising hopes for a simpler and quicker diagnostic process. So what does the new test involve? Brain scans? A quicker psychiatric assessment? Not quite. Of all places, it seems the best place to test for autism could be in your poop…
Believe it or not, researchers have discovered consistent differences in the gut microbiome – the community of trillions of microbes in your intestines – of individuals with autism compared to those without.
In fact, a routine stool sample could help doctors identify autism much earlier than current methods allow.
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“There's a real unmet need in a delayed diagnosis in children with autism because a lot of these kids have symptoms that are very variable,” study co-author Prof Siew Chien Ng tells BBC Science Focus.
Autism is pretty common – around 1 in 100 people have it, according to the World Health Organisation – yet its exact causes are not well understood. Genetics are thought to play a key role, but a whole host of other factors could be involved.
These include birth complications, exposure to air pollution and even sex – males are nearly four times more likely to be diagnosed with autism (although research has highlighted it could be vastly under-diagnosed in females).
This, alongside the differences in symptoms that autistic people display, makes getting a diagnosis difficult, and nigh on impossible in very young children.
Currently, diagnosis relies on behavioural assessments and developmental screenings. These methods can be subjective, time-consuming and reliant on the availability of trained specialists.
According to data from Drexel University, for example, the average age of diagnosis in the US is five years old. That lag time means children could miss out on vital care and support during a crucial period of early development.
The study, published in the journal Nature Microbiology, analysed stool samples from 1,627 children aged one to 13, some of whom were autistic. The team found that gut microbes differed markedly in children with and without autism.
They identified 51 types of bacteria, 18 viruses, 14 archaea, seven fungi and a dozen metabolic pathways that were altered in autistic children.
Using a machine learning algorithm, the scientists could identify autistic children with up to 82 per cent accuracy based on 31 microbes and biological functions in the digestive system.
“We identified that it's not just the bacteria that matters, it's the whole ecosystem in the gut microbiome,” says Ng.
“All in all it provides hope that we may have a stool test which is non-invasive to help facilitate the detection of autism.”
The simple test could be available by the end of the year, and for the parents would be as straightforward as collecting the sample in a bottle and sending it off to a lab. From there, results could be available within a week.
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How is the gut microbiome linked to autism?
Ng explains that there are two main ways in which the gut microbiome of an autistic person differs from a neurotypical gut.
“The first difference is that autistic people have reduced diversity in their gut. So the types of bacteria, the types of viruses; the numbers are less and the types of them are less as well.”
“The second thing we find is that in these children's gut, they have more of what we call ‘pathogenic bacteria’. So those that are less favourable and can produce certain toxins.”
Ng refers to this as a sort of chicken or egg scenario – experts aren’t sure whether these differences contribute to autism or are caused by it. For example, people with autism often have poorer diets, which can reduce the diversity and health of their gut.
On the other hand, some gut microbes are responsible for breaking down chemicals into neurotransmitters for use in the brain, which could play a role in the symptoms of autism.
One study, for example, found that introducing gut bacteria from autistic people to mice caused them to display autistic-like behaviours. But then again, mice are not humans, and experts have expressed doubt over how well if at all autistic-like behaviour can be discerned from the furry lab assistants.
If the researchers’ thinking is correct, and disruption to the microbiome does affect the severity of autism, it raises the prospect of personalised interventions that use diet or live bacteria known as probiotics to establish a more diverse microbiome in those diagnosed with the condition.
Early results from work conducted by Ng and her colleagues have shown promise, she says. “If you modulate the microbiome, symptoms actually improve as reported by the parents. So, I think the next step is to run a randomised control trial to see if we can do that.”
Still, she urges caution, saying that the results do not imply causality. “We cannot say that these biomarkers we identified cause autism. We can say that it's present and we found them in these children with autism.”
The team is now running a clinical trial to investigate whether stool samples can help identify autistic children as young as one year old.
Other details need ironing out, too. For example, the study population was majority Chinese and regional diet can influence the gut microbiome.
“We need to do more work globally now, to get the accuracy higher in the United States, Europe and other areas of Asia. But, for now, we are quite happy to see consistently high diagnostic performance regardless of what type of diet people have,” Ng says.
About our expert
Siew Ng is a professor at the Department of Medicine and Therapeutics and Assistant Dean (Development) of the Faculty of Medicine of the Chinese University of Hong Kong. Her research utilises the gut microbiota for the diagnosis and treatment of human diseases including inflammatory bowel disease, colorectal cancer, obesity, metabolic syndrome, autism, allergy, multidrug-resistant infections, and clostridioides difficile infections. Her team has developed microbial markers to predict disease risks in children and adults.
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