Environmental and genetic risk factors are both known to contribute to autism. Theo D. Palmer and his colleagues at Stanford University in California studied how a relatively common genetic risk factor may make developing fetuses more vulnerable to the mother’s immune response to illness or infections during pregnancy.

The genetic risk factor involves a gene that is known to regulate neural circuit activity in the brain. The same gene, GABRB3, has been shown to regulate immune response. Palmer and his team predict that defects in this autism risk gene also increase the magnitude of an immune response, thereby amplifying the risk associated with illness during pregnancy.

Palmer and his team examined the effects of a maternal illness during pregnancy in mice. In a paper published in 2013 by Pamela Carpentier and her colleagues in the Journal of Neuroscience, the team describes how maternal illness in the absence of genetic risk factors can generate striking differences in brain development and function in the fetus¹. They also previously discovered that illness-induced placental damage plays a significant role in this process².

Palmer and his team showed that mice carrying autism-related defects in the GABRB3 gene have greatly increased placental sensitivity to immune events during early to mid-pregnancy. This demonstrates a direct interaction between genetic and environmental risk factors in autism. The researchers speculate that genetic risk factors in the fetus, along with an environmental risk such as illness during pregnancy, may be sufficient to cause autism. Palmer and his colleagues also identified clinically approved drugs that greatly reduce the impact of illness in mice that carry this genetic risk factor.