A new type of probiotic therapy may reverse cognitive and behavioural symptoms associated with autism spectrum disorders, scientists say.
Researchers at the California Institute Technology (Caltech) are the first to demonstrate that changes in the gut bacteria can influence autism-like behaviours in a mouse model.
"Traditional research has studied autism as a genetic disorder and a disorder of the brain, but our work shows that gut bacteria may contribute to ASD-like symptoms in ways that were previously unappreciated," said Professor of Biology Sarkis K Mazmanian.
To study this gut-microbiota-brain interaction, the researchers used a mouse model of autism.
In humans, having a severe viral infection raises the risk that a pregnant woman will give birth to a child with autism, researchers said.
Researchers reproduced the effect in mice using a viral mimic that triggers an infection-like immune response in the mother and produces the core behavioural symptoms associated with autism in the offspring.
They found that the "autistic" offspring of immune-activated pregnant mice also exhibited gastrointestinal (GI) abnormalities.
In particular, the GI tracts of autistic-like mice were "leaky," which means that they allow material to pass through the intestinal wall and into the bloodstream.
This characteristic, known as intestinal permeability, has been reported in some autistic individuals.
"To our knowledge, this is the first report of an animal model for autism with comorbid GI dysfunction," said Elaine Hsiao, first author on the study.
To see whether these GI symptoms actually influenced the autism-like behaviours, the researchers treated the mice with Bacteroides fragilis, a bacterium that has been used as an experimental probiotic therapy in animal models of GI disorders.
Observations of the treated mice showed that their behaviour had changed. In particular, they were more likely to communicate with other mice, had reduced anxiety, and were less likely to engage in a repetitive digging behaviour.
"The B fragilis treatment alleviates GI problems in the mouse model and also improves some of the main behavioural symptoms," Hsiao said.
"This suggests that GI problems could contribute to particular symptoms in neurodevelopmental disorders," said Hsiao.
With the help of clinical collaborators, the researchers are now planning a trial to test the probiotic treatment on the behavioural symptoms of human autism. The trial should begin within the next year or two, researchers said.
The study was published in the journal Cell.
