WASHINGTON - The parents of two 10-year-old boys who believe vaccines caused their sons to develop autism brought their case to U.S. federal court on Monday, arguing a mercury preservative in the shots caused a rare reaction.

Their case is the second of three being heard by a special court trying to determine if autism might sometimes be caused by vaccines. Although most medical experts say there is no link, the court can rule there is a plausible association and allow parents of children with autism to get federal compensation from a special vaccine fund.

More than 5,300 cases have been filed by parents who believe vaccines may have caused autism in their children and are seeking payment under the National Vaccine Injury Compensation Program, a no-fault system that pays out for vaccine injuries.

Under the program, someone injured by a vaccine does not have to prove the vaccine actually caused his or her injuries.

All that is necessary is to prove that vaccines sometimes cause that particular condition or injury. The no-fault payout system is meant to protect vaccine makers from costly lawsuits that drove many out of the vaccine-making business.

Payouts in such cases sometimes top $1 million. The compensation program is funded by a 75-cent tax on vaccinations.

The court is hearing three different theories on how vaccines might cause autism. One is that a combination vaccine for measles, mumps and rubella, or MMR, plus a mercury-containing preservative called thimerosal, can cause autism. The court heard those arguments last year and has not ruled.

On Monday, the court began hearing arguments that thimerosal in various vaccines might have caused autism in William Mead and Jordan King, both 10 and both from Portland, Oregon.


"What we will conclude ... is that thimerosal-containing vaccines belong on the list of environmental factors ... when one is evaluating what might have caused autism in a child when all of the other theories have been ruled out," attorney Tom Powers told the court in opening arguments.

He said the boys had conditions that made them especially vulnerable to the mercury in thimerosal.

"The evidence is indirect and it is circumstantial but it is supportive of the general theory of causation," he said.

No one knows what causes autism, which can severely disable a child with symptoms ranging from severe social avoidance to repetitive behaviors and sometimes profound mental retardation.

The U.S. Centers for Disease Control and Prevention estimates that about one in every 150 children has autism or a related disorder such as Asperger's syndrome.

Doctors agree there is a genetic link, and probably that something in the environment, possibly even conditions in the womb, can cause the brain effects that lead to symptoms.

While many studies have shown the thimerosal in vaccines has not caused autism, a vocal group argues the government and other experts are ignoring or covering up the evidence. Thimerosal has now been removed from most childhood vaccines.

"I think we will be able to convince you that the epidemic is real, that the increase is real," Mike Williams, another attorney for the boys, told the three "special masters" hearing the cases.

"The debate is over. There is no controversy," government attorney Lynn Ricciardella retorted in her opening arguments.

"The credible scientific community has already spoken on this issue and has rejected it."

Some autism activists have seized on the case of Hannah Poling, a girl from Georgia who won a case claiming a vaccine caused autism-like complications from a rare disorder.

The activists say it proves the federal courts gave in on the argument, but the government says Poling's case, which was removed from the special process and heard separately, was an exception and cannot be used as a precedent.