When California Institute of Technology (Caltech) researchers treated mice bred to display autism-like behaviors with a probiotic therapy, they found that the mice were more communicative, less anxious and less likely to engage in repetitive digging behavior. The findings are published online in the December 5 issue of the journal Cell.
This is the first study to demonstrate that changes in gut bacteria can influence autism-like behaviors, researchers noted.
"Traditional research has studied autism as a genetic disorder and a disorder of the brain," study researcher Sarkis K. Mazmanian, a professor of biology at Caltech, said in a statement. "But our work shows that gut bacteria may contribute to [autism-like] symptoms in ways that were previously unappreciated."
Researchers developed mice with autism-like symptoms by referring to a previous finding that severe viral infection during pregnancy seems to increase the risk the child will have autism. So, the researchers triggered an infection-like immune response in pregnant mice, which led to offspring with autism-like symptoms.
The researchers found that the gastrointestinal tracts of these mice were "leaky," meaning material was able to pass through the intestinal wall and into the bloodstream. The researchers treated the mice with Bacteroides fragilis, a bacterium that has been used as an experimental probiotic therapy on gastrointestinal disorders in animal studies.
The results were exciting: Not only was the leaky gut corrected, but the mice became more communicative and less anxious.
Because of the study's success, within the next year or so, the researchers plan to begin clinical trials of the probiotic treatment on humans with autism. About 1 in 50 U.S. children ages 6-17 have an autism spectrum disorder, according to a report based on a national survey of parents in 2011 and 2012 by the Centers for Disease Control and Prevention.
Many parents of a child with autism report that their child has digestive problems. However, the relationship between autism and digestive problems or "leaky gut" is disputed. It is unclear if digestive problems contribute to autism, or if the stress of autism causes digestive problems.
According to a study last month from the University of California, Davis, children with autism are far more likely to have digestive problems than those without autism. However, a study published in Pediatrics in 2010 found there is no strong evidence that digestive problems are more common in children with autism or that special diets work.
Caltech researchers caution that much more work is needed before a reliable probiotic can be developed as a therapy for human autism.
"Autism is such a heterogeneous disorder that the ratio between genetic and environmental contributions could be different in each individual," Mazmanian said in the press release. "Even if B. fragilis ameliorates some of the symptoms associated with autism, I would be surprised if it's a universal therapy -- it probably won't work for every single case."
Betty Diamond, an immunologist at the Feinstein Institute for Medical Research in Manhasset, New York, told Science Magazine that this Caltech study "shows us something fabulous." She also stressed that it would be premature to use B. fragilis on humans, saying "we don't really understand" which bacterial species are important or how they colonize the gut.
Still, Mazmanian is optimistic about the treatment's potential, saying "I think our results may someday transform the way people view possible causes and potential treatments for autism."