http://www.sciencedaily.com/releases/2004/06/040609072439.htm
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Source:
Molecular Psychiatry
Date:
2004-06-09
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Thimerosal, Found In Childhood Vaccines, Can Increase The Risk Of
Autism-like Damage In Mice
A new study indicates that postnatal exposure to thimerosal, a mercury
preservative commonly used in a number of childhood vaccines, can lead
to the development of autism-like damage in autoimmune disease
susceptible mice. This animal model, the first to show that the
administration of low-dose ethylmercury can lead to behavioral and
neurological changes in the developing brain, reinforces previous
studies showing that a genetic predisposition affects risk in
combination with certain environmental triggers. The study was conducted
by researchers at the Jerome L. and Dawn Greene Infectious Disease
Laboratory at the Mailman School of Public Health, Columbia University.
Over the past 20 years, there has been a striking increase--at least
ten-fold since 1985--in the number of children diagnosed with autism
spectrum disorders. Genetic factors alone cannot account for this rise
in prevalence. Researchers at the Mailman School, led by Dr. Mady
Hornig, created an animal model to explore the relationship between
thimerosal (ethylmercury) and autism, hypothesizing that the combination
of genetic susceptibility and environmental exposure to mercury in
childhood vaccines may cause neurotoxicity. Cumulative mercury burden
through other sources, including in utero exposures to mercury in fish
or vaccines, may also lead to damage in susceptible hosts. Timing and
quantity of thimerosal dosing for the mouse model were developed using
the U.S. immunization schedule for children, with doses calculated for
mice based on 10th percentile weight of U.S. boys at age two, four, six,
and twelve months.
The researchers found the subset of autoimmune disease susceptible mice
with thimerosal exposure to express many important aspects of the
behavioral and neuropathologic features of autism spectrum disorders,
including:
* Abnormal response to novel environments;
* Behavioral impoverishment (limited range of behaviors and decreased
exploration of environment);
* Significant abnormalities in brain architecture, affecting areas
subserving emotion and cognition;
* Increased brain size.
These findings have relevance for identification of autism cases
relating to environmental factors; design of treatment strategies; and
development of rational immunization programs. The use of thimerosal in
vaccines has been reduced over the past few years, although it is still
present in some influenza vaccines. Identifying the connection between
genetic susceptibility and an environmental trigger for autism--in this
case thimerosal exposure--is important because it may promote discovery
of effective interventions for and limit exposure in a specific
population, stated the lead author Dr. Mady Hornig. Because the
developing brain can be exposed to toxins that are long gone by the time
symptoms appear, clues gathered in these animal models can then be
evaluated through prospective human birth cohorts--providing a powerful
to tool to dissect the interaction between genes and the environment
over time.
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Citation source: Molecular Psychiatry 2004 Volume 9, advance on line
publication doi:10.1038/sj.mp.4001529
ARTICLE: "Neurotoxic effects of postnatal thimerosal are mouse
strain-dependent"
M Hornig, D Chian, W. I. Lipkin
Greene Infectious Disease Laboratory, Mailman School of Public Health,
Columbia University, 722 W 168th St, New York, New York 10032
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Molecular Psychiatry is published by the Nature Publishing Group.
http://www.nature.com/mp
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This story has been adapted from a news release issued by Molecular
Psychiatry.