The parents of two 10-year-old boys who believe that a mercury-based preservative, thimesoral, found in many childhood vaccines, caused their sons to develop autism brought their case to U.S. federal court on Monday.

Autism is a brain development disorder that appears before a child turns three years old; it has a serious impact on social interaction and communication. Medical experts do not know for sure what exactly causes autism, but they do know there is a strong hereditary component.

According to the U.S. Centers for Disease Control and Prevention, about one in every 150 children has autism or a related disorder such as Asperger’s syndrome.

Overall, more than 5,300 families have filed claims with the U.S. Court of Claims alleging that vaccines caused autism and other neurological problems in their children. They are seeking payment under the National Vaccine Injury Compensation Program, a no-fault system that pays out for vaccine injuries.

The two boys from Portland, Ore., William Mead and Jordan King will serve as test cases to determine whether thousands of families can be compensated. Thomas Powers, one of their attorneys and his colleagues will try to show they were in good condition, but, after being exposed to vaccines with thimesoral, they started having problems.

"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," Powers told the court in opening arguments, as quoted by Reuters. He also added that the boys had conditions that made them especially vulnerable to the mercury in thimesoral. “The evidence is indirect and it is circumstantial but it is supportive of the general theory of causation.”

In 2007, the court held hearings saying that a combination vaccine for measles, mumps and rubella, or MMR, plus a mercury-containing preservative called thimesoral can cause autism, but has no ruled.

The theory, according to which thimesoral in vaccines can cause autism is not accepted by many medical experts, including the Institute of Medicine, the U.S. Centers for Disease Control and Prevention and the American Academy of Pediatrics.

Also, multiple scientific studies have not proved a link and this was what U.S. Justice Department attorney Lynn Ricciardella mentioned in her opening. “There is no scientific debate. The debate is over. The credible scientific community has already spoken on this issue and has rejected it. There is no controversy,” she said, according to the Associated Press.

Over the past years, many pharmaceutical companies have removed thimesoral from their vaccines intended for children, except flu vaccines, but its removal has appeared to have no effect on autism rates.

Ricciardella also argued that the connection between thimesoral and autism was first made public by a journal called Medical Hypothesis, which she described as willing to publish radical ideas as long as they are coherent. She even pointed to the fact that authors pay to have their article published.

If the parents’ appeal is successful, they could receive compensation for past and future medical expenses, special education expenses and up to 250,000 U.S. dollars for pain and suffering, among other money.