May 12 (HealthDay News) -- A preservative containing mercury and once widely used in childhood vaccines becomes the topic of a U.S. lawsuit this coming week as two Oregon families seek to prove that the substance caused two 10-year-old boys to develop autism.

The Associated Press reported that the boys' families are the first of 4,900 families to charge in court that the preservative thimerosal does indeed trigger autism in some children. The case is being heard in the U.S. Court of Claims.

A number of studies in recent years have found there was no evidence that thimerosal had any link to the onset of autism after a child had received one or more of the standard childhood vaccinations, the wire service said. In 2004 a committee from the Institute of Medicine concluded that thimerosal did not cause autism when used as a vaccine preservative, the AP reported.

Today, however, only the influenza vaccine contains thimerosal. The attorneys for the boys must prove that autism was caused by the vaccines, which at the time the children were injected contained thimerosal, the wire service reported.

According to interviews and examination of the court documents, the AP reported that the plaintiffs will attempt to present evidence that injections with thimerosal deposit a mercury variant in the brain. This, in turn, excites certain brain cells, which leads to autism.

"In some kids, there's enough of it that it sets off this chronic neuroinflammatory pattern that can lead to regressive autism," attorney Mike Williams told the AP.