One in 160 children suffers from some kind of autism spectrum disorder (ASD), according to the World Health Organization. These are a series of alterations in brain development characterized by a wide range of symptoms and levels of disability and while some children have slight damage, others can be seriously disabled.
Although a range of factors are usually considered, the exact cause of these anomalies is unknown. Recent research carried out by scientists from the California Institute of Technology (Caltech) and published in the journal Cell seems to shed some light on the origin of the condition, which, it appears may be linked to changes in the gut microbiota.
Prior studies had shown a relationship between the 100 trillion bacteria living in the colon and in animals’ behaviour. In fact, it is known that these microorganisms play a role in anxiety, as well as in the animals’ perception of pain and even emotional response. “Our work is the first one to test whether, if we modulate gut microbiota, we can influence the symptoms of autism in mice,” explained researcher Elaine Hsiao to Gut Microbiota Worldwatch during the 4th Gut Microbiota for Health World Summit in Barcelona. The work by this American scientist was one of the pieces that created the most expectation at the annual international meeting of experts.
“In our laboratory, we were studying the development of the immune system in mice and wanted to see if, by acting on the gut microbiota, we could train these animals’ defences. As soon as we started the study, we observed that there is a significant amount of clinical studies reporting that people with autism tend to have major gastrointestinal problems. This, in some way, gave us the clue to start researching,” said Hsiao.
Epidemiological evidence in humans shows that if the mother has a major immune response during a certain stage of her pregnancy, there is an increase in the risk of the child suffering from ASD. Based on this knowledge, Hsiao and her team provoked an immune response among pregnant female mice, leading to a new generation with symptoms typical of ASD, from repetitive movements to less interaction and communication with other mice.
Furthermore, these animals’ microbiota was altered and the permeability of their intestines was significantly increased compared to healthy mice, which is a risk as potentially harmful or toxic substances can leak from the intestine into the bloodstream. And this may be what happens to some children suffering from ASD with diarrhoea.
Likewise, the team of scientists identified a molecule in the ASD mice, produced by the gut bacteria’s metabolism and very similar to another that is found at high concentrations in children diagnosed with ASD. To find out the exact function of this metabolite, the researchers administered it to healthy mice and they quickly started to show behavioural symptoms similar to the ASD mice. This finding suggests that the potentially toxic molecules leak from the intestine, are filtered into the bloodstream and reach the brain.
On the other hand, Hsiao and her team tested a probiotic treatment with Bacteroides fragilis, a commensal microbe found in healthy intestines and which had been effective in previous studies in treating immune as well as gastrointestinal problems. After giving this bacteria to the autistic mice, they saw how their gut problems improved, opening the door to developing new drugs that fight the symptoms of autism.
Although the findings of these initial studies are promising, Hsiao was cautious and repeated that, for now, these results are restricted to animal models and it is unknown whether they can be fully transferred to humans.