Concern has been expressed over the possibility that the mercury-containing compound thimerosal in vaccines may cause autism.1–4 Thimerosal is sodium ethylmercury thiosalicylate, an organic compound of ethyl mercury, included in certain vaccines to protect multiple dose ampules from bacterial and fungal contamination. Mercury in sufficient dose is neurotoxic, and probably more toxic in the immature brain. It is reasonable to ask whether thimerosal in childhood vaccine increases risk of chronic childhood neurologic disability and specifically of autism. The available data with which to address the question are very limited and largely inferential. Most of the information we have about mercury toxicity is related to exposure to methyl rather than ethyl mercury.
Bernard et al1 offered an hypothesis that autism is an expression of mercury toxicity resulting from thimerosal in vaccines. They base this hypothesis on their views2 that the clinical signs of mercury toxicity are similar to the manifestations of autism, that the onset of autism is temporally associated with immunization in some children, that the recent increase in diagnosis of autism parallels exposure to thimerosal, and that there are higher levels of mercury in persons with than without autism.
This review will examine these issues and others to ask whether, according to evidence now available, thimerosal is a probable cause of autism. We will not discuss which, if any, of the differing guidelines designed to limit exposure to mercurials is appropriate for deciding whether thimerosal in vaccines is in all regards safe for children. Our focus is on a narrower but important question: whether current evidence indicates that mercury at any known dose, form, duration, age, or route of exposure leads to autism.
ARE THE CLINICAL MANIFESTATIONS OF AUTISM SIMILAR TO THOSE OF RECOGNIZED MERCURY TOXICITY?
Bernard et al1 present a table listing ∼95 clinical findings they consider to be shared by autism and mercury poisoning. …