WASHINGTON (AP) - There is no evidence that a controversial mercury-based vaccine preservative causes autism, concludes an eagerly anticipated scientific review that says it's time to lay vaccine suspicions to rest and find the real culprit.

Tuesday's conclusion by the prestigious Institute of Medicine pointed to five large studies, here and abroad, that tracked thousands of children since 2001 and found no association between autism and vaccines containing the preservative thimerosal.

Many parents of autistic children blame vaccination for the brain disorder.

But the panel of prominent scientists said that while high doses of mercury can cause neurological damage, there's no evidence that this type of damage causes the symptoms specific to autism - and no laboratory or animal research that proves how the much smaller amounts of mercury in thimerosal could do so either, the IOM concluded.

On the other hand, genetics plays a role in autism, and several studies show clear signs of prenatal onset of the disorder, including brain differences at birth, the report notes.

"Don't misunderstand: The committee members are fully aware that this is a very horrible and devastating condition," said Dr. Marie McCormick, a Harvard professor of maternal and child health who led the IOM probe. "It's important to get to the root of what's happening."

But, "there seem to be lots of opportunities for research that would be more productive" than continuing the vaccine hunt.

Autism is a complex developmental disorder best known for impairing a child's ability to communicate and interact with others. Recent data suggest a tenfold increase in autism rates over the last decade, although it's not clear how much of the apparent surge reflects better diagnosis and how much is a true rise.

Thimerosal has been used as a preservative in some vaccines and other medicines since the 1930s. Although the amount of mercury it contains is very small, vaccine makers began phasing out thimerosal in 1999 as a precaution urged by public health officials. It now has been virtually eliminated in routine childhood vaccines.

Vaccine critics didn't immediately comment on the report.

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