William Eaton, chairman of the Department of Mental Health at the Bloomberg School of Public Health at Johns Hopkins University and his 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 disorders. 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 coeliac disease it's more than three times but, as the researchers said, the figures were enough to impress an epidemiologist, but not enough to make anybody in the general population change their behaviour.

Dr Hjordis 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 but that the results should not cause worry or be unsettling for parents or future parents with any of the above mentioned diseases as 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 confirms that they 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. Although there seems to be a connection between autism and some parental autoimmune diseases the mechanism of that interaction is not known. It could be associated with the diseases themselves, or that the genes associated with autoimmune diseases and autism are located near each other, or that an autoimmune disease changes the quality of a pregnancy, which results in circumstances that increase the risk for autism.

Pediatrics on line July 6 2009

First published in September 2009

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