Study Finds No Link Between Autism And Thimerosal In Vaccines

Study Finds No Link Between Autism And Thimerosal In Vaccines


Science Daily — The increase in the number of diagnosed cases of autism
in recent years has sparked concern that environmental toxins may cause
this complex disorder. However, a new University of Missouri-Columbia
study concludes that exposure to Rh immune globulin preserved with
mercury-containing thimerosal before birth was no higher for children
with autism.


"This study adds to the evidence that there is no casual association
between thimerosal and childhood autism," said Judith Miles, who is the
William S. Thomson Endowed Chair of Autism and professor of pediatrics
and pathology in the MU School of Medicine. "We conclude that there is
no indication that pregnancies resulting in children with autism were
more likely to be complicated by Rh immune globulin/thimerosal exposure."

The study investigated thimerosal exposure during pregnancies that
resulted in the birth of a child subsequently diagnosed with autism.
Although experts anticipate that autism will be the first
behavioral/psychiatric disorder for which major genes will be
identified, there is still fierce debate that thimerosal, a preservative
commonly used in vaccines and is almost 50 percent ethylmercury, is
responsible for the rise in the disorder. Rh negative women are
routinely treated with Rh immune globulin (RhIg) during the third
trimester to prevent hemolytic disease, in which the mother's immune
system attacks fetal blood cells. Like many vaccines, RhIg manufactured
in the United States contained thimerosal prior to 2001. Since young
fetal brains are more susceptible to neurotoxic effects, researchers led
by Miles, of the MU Thompson Center for Autism and Neurodevelopmental
Disorders, assessed Rh status and thimerosal exposure of mothers of
children with autism.

The study included 214 mothers of 230 children diagnosed with an autism
spectrum disorder. Rh status, RhIg with thimerosal exposure and Rh
incompatibility (in which the mother's Rh status is different than the
fetus's) were established by reviewing medical records. The results
showed that in children with autism, Rh negative status was no higher in
their mothers than in the general population, that exposure to RhIg
(preserved with thimerosal) before birth was no higher and that
pregnancies were not more likely to be Rh incompatible.

"We hope this report of no association between autism, Rh negativity and
thimerosal exposure during pregnancy will offset some of the decreased
compliance with immunization recommendations which is known to increase
morbidity and mortality from childhood infectious diseases," Miles said.

Autism diagnoses have increased significantly during the past two
decades, which coincides temporally with the addition of five pediatric
vaccines to the immunization schedule, exposing children to increasing
doses of ethylmercury, a known toxin. Though the vast majority of
studies indicate no association between vaccines and autism, the FDA,
CDC and American Academy of Pediatrics recommended that thimerosal be
removed from all routinely recommended early childhood vaccines; this
was accomplished by 2002.

Miles points out that even though RhIg and childhood vaccines are now
free of thimerosal in the United States, it is important to analyze
questions of safety since thimerosal continues to be used in many places
around the world to preserve vaccines to help make them affordable.

Miles said that few studies have focused on pregnancies of Rh negative
mothers who received RhIg during pregnancy, probably because the
thimerosal is diluted before reaching the fetus and has been assumed to
be innocuous. Nevertheless, there is a concern that even very small
doses delivered when the brain is especially sensitive can be toxic.
Numerous Internet sites and one research study assert that RhIg causes
autism and that a high percentage of mothers of children with autism are
Rh negative, neither of which was shown to be true in the current study.
In addition, a recent study hypothesized that Rh incompatibility itself
could disrupt fetal neurodevelopment, thus playing a role in autism, but
the current study found no increase in the proportion of Rh
incompatibility in mothers of autistic children. In response to the
claim that only certain groups of children are at risk, the authors also
analyzed specific autism spectrum disorder subgroups and found that none
had significant increases in either Rh negativity or thimerosal exposure
during pregnancy.

The study -- "Lack of Association Between Rh Status, Rh Immune Globulin
in Pregnancy and Autism" -- was published in the May 2007 issue of the
American Journal of Medical Genetics.

Note: This story has been adapted from a news release issued by
University of Missouri-Columbia.