Parents often report that tummy troubles and autism go hand in hand. Some have even suggested that special diets can reduce autism symptoms. But many experts have dismissed the connection as mere coincidence or have attributed the overlapping conditions to different genetic or environmental factors.
Now new research, published in the March Pediatrics, shows that there is a genetic link between autism and gastrointestinal disorders. It’s unclear whether this genetic link means that an environmental therapy such as diet could boost brain function or if just feeling better could be responsible for improved behavior.
Researchers from Vanderbilt University had previously linked a genetic variant in the control panel of the MET gene to autism. In the general population, some people have the DNA letter G in a particular position in the control panel, which determines whether the MET gene is active. Other people have a C in that position. That variant of the gene, known as the MET C allele, turns down production of MET, a protein involved in brain development, gut repair and other body functions. Children who inherit copies of MET C from both parents have more than twice the risk of developing autism as children who get the G variety from both parents.
In the new study, the Vanderbilt team and additional colleagues found that children with autism who have two copies of MET C are also more likely to have gastrointestinal problems than people who have two copies of the G variant or a combination of G and C. The study is the first to demonstrate a possible genetic cause for the co-occurrence of autism and digestive tract problems.
Some people sampled in the study also have a double dose of the MET C allele but have neither autism nor reported gastrointestinal problems. There are also children with two C versions who have autism but not stomach problems.
Identifying such variants will help doctors subdivide autism into different categories and aid in tailoring treatments for the disorder, says Daniel Campbell, a geneticist at Vanderbilt School of Medicine in Nashville, Tenn., who led the study. But finding a common cause for the two conditions doesn’t mean that autism is caused by stomach problems, he says. And changing the diet of a child with autism may improve their mood and behavior, but won’t alter the underlying brain problems that cause autism.
“The change in diet is not changing brain structure, it’s just making the kid feel less sick,” he says.
Martha Herbert, a pediatric neurologist at Massachusetts General Hospital’s Center for Morphometric Analysis in Charlestown, and Harvard University Medical School applauds the discovery. “What they’ve shown is that [autism and gastrointestinal disorders] are co-occurring,” Herbert says. “That’s a very welcome development, and these people should be commended for recognizing that autism doesn’t just affect the brain, it affects the whole person.”
Herbert says though she is in the minority, she thinks that autism may result not from subtle differences in brain structure but from bodywide dysfunction in cells. The MET gene may be one example; when the gene’s activity is disrupted, multiple body functions go wrong, including brain activity and digestive system function. Treatments that alter MET’s activity or affect a network of which MET is a part may improve both bellyaches and autism symptoms, she says.