A recent study concluded thimerosal, a mercury preservative commonly found in some childhood vaccines, can spur the development of autism-like damage in autoimmune-disease- susceptible mice. This model is the first to show low doses of mercury can lead to behavioral and neurological alterations in developing brains. It also supports previous studies demonstrating that environmental triggers and genetic factors affect the risk of autism.

Interest in the link between mercury and autism isn’t surprising, because genetic factors alone don’t account for the tenfold climb in autism over the past two decades. Over the course of the study, researchers found the mice exposed to thimerosal showed many behavioral and neuropathological features of autism disorders:

• Larger brain sizes
• Limited ranges of behaviors in addition to a decreased exploration of environments
• Abnormal responses to unique environments
• Deviations in brain architecture affecting areas that control emotions and thought

The cumulative exposure to mercury through other sources, including pre-birth exposure to fish, can also lead to damage. Why? The brain can suffer from exposure to toxins that have disappeared long before symptoms are noticed.

For the study, thimerosal testing on mice was developed by using the nation’s immunization schedule for children, with doses based on the weights of U.S. boys ages 1, 2, 4 and 6. Although thimerosal is still used in some flu vaccines, its presence has been reduced in the past few years, according to researchers.

Finding the link between genetic susceptibility and environmental triggers for autism is important, researchers said, because it promotes more research into effective safeguards that can limit or sidestep exposure in specific age groups to thimerosal. The data is also valuable in terms of comparing the results in mice to human babies, and dissecting the interaction between the environment and genes over time.

Molecular Psychiatry June 8, 2004