Children with autism, more accurately called "autistic spectrum disorders," live under heart-rending circumstances. Many shun human companionship, seeming not to notice when a parent or playmate tries to engage them. Some do not speak, or they communicate only in mimicked phrases and non sequiturs. Some seemed trapped in endless cycles of repeated behaviors or routines, becoming agitated or alarmed when the activity is altered. Some may master difficult tasks with ease, tough mathematical calculations for instance, but be utterly at a loss for what waving "hello" is supposed to mean.
While the exact number of cases is unknown, the Centers for Disease Control and Prevention report that in 2003 more than 140,000 children in the United States were classified as autistic for special education purposes. The CDC says also that, based on prevalence data, some 24,000 American children are likely to be diagnosed each year.
Doctors are puzzled by the disorder's causes. They say it may be genetically determined, that environmental causes may play a role, or both. Such surmises are of little comfort to anxious parents who, confronted with science's lack of certainty, have sometimes rushed to embrace less-than-reliable explanations.
Chief among these are Internet and cable-television-fueled rumors that the onset of autism is related to either the measles-mumps-rubella (MMR) vaccine or, more specifically, to thimerosal, a mercury-containing compound once widely used as a preservative in vaccines and other biological products.
That thimerosal is no longer used in vaccinations intended for children has done little to quell fears.
According to autism expert Judith Miles, a professor of pediatrics and the Thompson Endowed Chair of Child Health and Pathology at MU, such concerns represent a classic case of parents confusing correlation with causation. "Many children with autism start to develop autistic symptoms around the same time as they receive immunizations," Miles says. "Obviously, it is worrisome to families and it seems reasonable to conclude that a relationship exists."
Reasonable, she says, if one ignores dozens of peer-reviewed studies from around the world saying otherwise. "If you look at the data there is simply no relationship between them," Miles says. "There has been no thimerosal in Denmark's vaccines since 1991 and yet diagnosed cases of autism there rose at the same rate as they did worldwide."
She adds that a 2004 CDC-sponsored review by a committee of independent experts at the Institute of Medicine -- part of the National Academy of Sciences in Washington, D.C. -- was categorical in its conclusions. "Neither thimerosal-containing vaccines nor the MMR vaccine are associated with autism," wrote the study's authors. "The hypotheses regarding a link between autism and MMR vaccine and thimerosal-containing vaccines lack supporting evidence and are only theoretical; future research to find the cause of autism should be directed toward other promising lines of inquiry that are supported by current knowledge and evidence and offer more promise for providing an answer."
Miles' own research supports this view. In her most recent investigation, she examined the medical records of women who had received Rh immune globulin shots during pregnancy. Because thimerosal is used in Rh immune globulin, Miles hypothesized that, if thimerosal did indeed present an autism risk, these women would almost certainly have given birth to a greater number of autistic children. In fact, they did not.
"We conclude that there is no indication that pregnancies resulting in autistic children were more likely to be complicated by Rh immune globulin/thimerosal exposure," Miles wrote. "These data suggest there is no role for thimerosal in the development of autism."
Miles presented the study, Rh Immune Globulin in Pregnancy: Relationship to Autism Development, at this year's national meeting of the American College of Medical Genetics.
Published by the Office of Research.
©2006 Curators of the University of Missouri. Click here to contact the editor.