Autism, Genetics and Environment - Study Finds Autism Immune System Link

A study reported in the January 2008 issue of Genomics, Gene expression changes in children with autism, has found that a group of genes with known links to natural-killer cells, that attack viruses, bacteria and malignancies, are expressed at high levels in the blood of children with autism when compared to children without the disorder. The study also found gene expression distinctions in children with early onset and regressive autism. The study is summarized in a digestible format on the UC Newsroom article Researchers identify gene expression profile distinctions in children with autism. Comments by the senior researcher Frank Sharp M.D. clinical neurologist, neuroscientist, and professor, department of neurology, school of medicine, indicate that the findings suggest a possible environmental role in the development of autism disorders:

"What we found were 11 specific genes with expression levels that were significantly higher in the blood of children with autism when compared to the blood of typically developing children," said Frank Sharp, senior author of the study and professor of neurology with the M.I.N.D. Institute.

"Those 11 genes are all known to be expressed by natural-killer cells, which are cells in the immune system necessary for mounting a defense against infected cells. We were surprised by our results because we were not looking for these particular genes. And while a number of studies have shown immune system dysregulation to be an important factor in autism, ours is one of the first to implicate these particular cells."

...

"What we are seeing can reflect something in the environment that is triggering the activation of these genes or something genetic that the children have from the time they were conceived," Sharp explained. "Such an immune response could be caused by exposure to a virus, another infectious agent or even a toxin.

Another possibility is that these changes represent a genetic susceptibility factor that predisposes children to autism when they are exposed to some environmental factor." He added that the current study also does not identify whether or not the natural-killer cells are functioning abnormally, which further work by M.I.N.D. Institute immunologists will reveal. "If the natural-killer cells are dysfunctional, this might mean that they cannot rid a pregnant mother, fetus or newborn of an infection, which could contribute to autism."

The study is also featured in an article by Carrie Peyton Dahlberg at sacbee.com which features several interesting comments by Dr. Jeffrey Gregg, director of molecular diagnostics for the UC Davis Medical Center who was also involved in the study. It is pointed out that both similarities and differences were found between the early onset and regression autism cases:

Children with that "regressive" autism had nearly 500 genes that were activated differently than children with "early onset" autism, Gregg and his colleagues found after examining blood samples from 61 children.

"That would suggest that those two groups are very different … and may have totally different underlying pathology," Gregg said.

Both groups, though, as well as other children with a range of symptoms called autism spectrum disorder, shared the 11 strongly expressed genes that control natural killer immune cells.

Dr. David Amaral, the UC Davis MIND Institute's research director suggested that much remains to be learned about how the genetic and environmental factors giving rise to autism interact:

It is still unclear how early those differences emerge, but other MIND Institute researchers are looking at immune differences in mothers' bloodstreams that might be predictive for having a child with autism, said Dr. David Amaral, the institute's research director.

"Things are moving really, really fast now," Amaral said, with scientists around the country working to understand the relationship of genetic and environmental factors that may underlie autism.

It seems clear from this study that environmental factors can not be ruled out in trying to understand the causes -- and potential treatments for autism. Some of the rhetoric which dismisses all genetic or all environmental factors appears to be ill founded. The Autism Knowledge Revolution is being carried out by researchers and scientists in relevant medical fields and the knowledge they are gaining appears to point to both genetics and environment as being involved in the development of autism.

autism