Epidemiological studies conducted over the past five years have identified a potential link between autoimmune diseases, particularly in the mother, and ASD. A 2009 study1 published in Pediatrics used the nationwide psychiatric health registry in Denmark to re-examine this issue, this time using a sample size over ten times larger than previously studied. Their findings confirmed an association between autoimmune disease and ASD.
Multiple research approaches have been used throughout the years to uncover a potential relationship between immune function and autism. Despite producing very intriguing data, the size of these studies has been limited, at times relying on retrospective self-reporting, and the findings have not always been replicated. Enter the authors of this new study, who took advantage of the nationwide health care system in Denmark to focus on the relationship between familial autoimmune diseases and ASD, including virtually all of the children born in the country between 1993 and 2004 (over 680,000 children). After locating those with diagnoses of an ASD, the authors used other databases to track down information on the presence or absence of twenty-six different autoimmune disorders in the parents or unaffected siblings. Their results confirmed previously reported links between familial type 1 diabetes and ASD, as well as between rheumatoid arthritis and ASD, discovering for the first time that rheumatoid arthritis in the mother, but not the father, is associated with increased risk for ASD. The authors also uncovered the first association between ASD and untreated celiac disease in mothers.
By using one of the largest and most comprehensive national health databases, this study provides additional clues regarding the association between immune system dysregulation and ASD. The associations found with specific autoimmune diseases and whether the disease is present in
mothers versus fathers provide important clues about the biologic mechanisms that may lead to autism. For instance, because the risk of ASD was increased only when the mothers, but not the fathers, had rheumatoid arthritis, the authors hypothesize that the link to autism may be due to exposure to maternal antibodies secreted during pregnancy, or other alterations within the prenatal environment. Indeed, one relatively new focus in the search for the causes of ASD is the complex interaction between the immune function of a mother during pregnancy and the biological impact this may have on the early brain development of her child [see 2008 Maternal Antibodies as a Biomarker]. On the other hand, because the association between type 1 diabetes and ASD was found if either parent was diabetic, this link may be explained by a genetic factor that is related to both diabetes and autism. In this way, the associations with familial autoimmunity reported in this study may be used to narrow down the search for autism risk factors, both genetic and environmental.