July 6 (HealthDay News) -- Children of mothers who have autoimmune diseases such as type 1 diabetes, rheumatoid arthritis and celiac disease have up to a three times greater risk for autism, a new study finds.
Although the association between autism and a maternal history of type 1 diabetes and rheumatoid arthritis had been found in earlier research, the researchers behind the new study say that theirs is the first to find a link between autism and celiac disease. People with celiac disease cannot tolerate gluten, a protein in wheat, rye and barley.
"This finding reinforces the suggestion that autoimmune processes are connected somehow with the cause of autism and autism spectrum disorder," said researcher William W. Eaton, chairman of the Department of Mental Health at the Bloomberg School of Public Health at Johns Hopkins University. "This finding is on the pathway of finding the cause of autism."
Eaton noted that there is no clinical significance to the finding but that it could guide future research as scientists try to pin down the cause or causes of autism.
One reason autoimmune diseases might have a role in autism is genetic, Eaton said. Children who are born underweight or premature are at higher risk for autism, and both of these obstetric problems are associated with celiac disease, he added.
"There may be an overlap in the genetics of some of the autoimmune diseases and autism that would not be trivial," he said. "Autism is strongly inherited, but we don't have the faintest idea where. But this may point a flashlight to areas of the genome that connect to autism."
In addition, there might also be environmental triggers that affect the fetus, he said.
The report is published in the July 6 online edition of Pediatrics.
For the study, Eaton's team collected data on 3,325 Danish children diagnosed with autism spectrum disorder, including 1,089 diagnosed with infantile autism. The children were born between 1993 and 2004, and their data was part of the Danish National Psychiatric Registry. Data on family members with autoimmune diseases came from the Danish National Hospital Register.
The researchers found that children whose mothers had autoimmune disease were at a higher risk of developing autism spectrum disorder than children of mothers who did not have these conditions. In addition, the risk of infantile autism was increased in children with a family history of type 1 diabetes.
The increased risk that autoimmune diseases contribute to autism is not huge, Eaton said.
"The increased risk for type 1 diabetes is a little less than two times, for rheumatoid arthritis it's about 1.5 times and for celiac disease it's more than three times," Eaton said. "That's enough to impress an epidemiologist, but not enough to make anybody in the general population start changing their behavior."
Dr. Hjordis O. Atladottir, from the Institute of Public Health at the University of Aarhus in Denmark and the study's lead researcher, said that the findings are important because they support the theory that autism is somehow associated with disturbances in the immune system.
"It is important to emphasize that these results should not cause worry or be unsettling for parents or future parents with any of the above-mentioned diseases," Atladottir said. "The large majority of people affected by an autoimmune disease do not have children with autism."
Autism expert Dr. Jeffrey Brosco, a professor of clinical pediatrics at the University of Miami Miller School of Medicine, said the study reinforces the association between autism and a mother's autoimmune disease or, in the cases of type 1 diabetes, a mother's or father's condition.
"This study confirms that we still don't know what's going on in autism but suggests there is something interesting about autoimmune diseases in parents of children with autism," Brosco said.
Though there seems to be a connection between autism and some parental autoimmune diseases, he said, the mechanism of that interaction is not known. It could be associated with the diseases themselves, it could be that the genes associated with autoimmune diseases and autism are located near each other or it could be that an autoimmune disease changes the quality of a pregnancy, which results in circumstances that increase the risk for autism, Brosco explained.
"These findings are not going to change anything anyone does," Brosco said. "You are not going to treat any patients differently. There is no strong evidence for changing clinical practice, but it does help scientists who are interested in autism understand what are the next questions to ask."
Geraldine Dawson, chief science officer for Autism Speaks, said that evidence is increasing that the immune system might have a role in autism.
"One of the things we are realizing about autism is that it is not one disease but rather many different diseases or conditions that has many different etiologies," Dawson said. "This may be one cause or one risk factor, and if it interacts with a genetic vulnerability, it can increase the risk for autism," she said.
SOURCES: William W. Eaton, Ph.D., Sylvia and Harold Halpert professor and chairman, Department of Mental Health, Johns Hopkins Bloomberg School of Public Health, Baltimore; Hjordis O. Atladottir, B.M., Institute of Public Health, Aarhus University, Denmark; Geraldine Dawson, Ph.D., chief science officer, Autism Speaks; Jeffrey Brosco, M.D., Ph.D., professor, clinical pediatrics, University of Miami Miller School of Medicine, Miami; July 6, 2009, Pediatrics