Can environmental exposures cause autism?

At this point, there is little evidence that environmental exposures can cause autism. One incident suggestive of a possible link between environmental exposures and autism is the Brick Township cluster in New Jersey. This town is located close to several Superfund sites (hazardous waste sites). The Centers for Disease Control and Prevention (CDC) found that autism was more common in this site than in the general population. [13] However, these results could have happened completely by chance.

The Agency for Toxic Substances and Disease Registry (ATSDR) found that three environmental contaminants, tetrachloroethylene, trichloroethylene, and trihalomethanes, were in the drinking water of Brick Township, NJ several times in the past. However, this information must be interpreted with great caution. There was no relationship between the location and timing of these abnormal chemical levels and cases of autism. [14] This example emphasizes the pressing need for more research into possible connections between environmental exposures and autism.

One of the most contentious issues in the environmental etiology of autism is the question of vaccines, the use of thimerosal (a mercury containing substance used as a preservative in vaccines), of mercury itself and of other so called “heavy metals”. This issue has unfortunately resulted in law suits and has split families apart. The Institute of Medicine Immunization Safety Review Committee examined the hypothesis that vaccines, specifically the measles-mumps-rubella (MMR) vaccine and thimerosal-containing vaccines, are causally associated with autism [20]:

“…the committee concludes that the evidence favors rejection of the causal relationship between thimerosal-containing vaccines and autism.”

“… the committee concludes that the evidence favors rejection of a causal relationship between MMR vaccine and autism”

“Because chelation therapy has potential serious risks, the committee recommends that it be used only in carefully controlled research settings….”

“The committee does not recommend a policy review ….. of vaccines”

The committee reviewed all available published and unpublished epidemiological studies regarding causality and studies of potential biologic mechanisms by which these immunizations might cause autism.
The committee concluded that the body of epidemiological evidence favors rejection of a causal relationship between the MMR vaccine and autism. The committee also concluded that the body of epidemiological evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism. The committee further finds that potential biological mechanisms for vaccine-induced autism that have been generated to date are theoretical only. The committee does not recommend a policy review of the current schedule and recommendations for the administration of either the MMR vaccine or thimerosal-containing vaccines. The committee recommends a public health response that fully supports an array of vaccine safety activities.
In addition, the committee recommended that available funding for autism research be channeled to the most promising areas. The committee made additional recommendations regarding surveillance and epidemiological research, clinical studies, and communication related to these vaccine safety concerns.

Conclusion:
  1. There is no evidence at present that autism is a mercury toxicity syndrome
  2. There is no evidence at present that autism is related to vaccination
  3. There is no evidence at present that autism is improved by chelation
Given the evidence that autism has a genetic component, environmental exposures may play a role in the development of autism through gene-environment interactions in susceptible individuals. [21] Several studies are currently underway to examine this interaction, which include the (Charge), Autism Birth Cohort (ABC) Study, and the Centers for Autism and Developmental Disabilities Research and Epidemiology (CADDRE). [3] These initiatives and many other studies will hopefully provide useful insight into the genetic and environmental causes of autism and other autism spectrum disorders.