another piece in the puzzle
New evidence suggests that inability to detoxify heavy metals plays a
role in autism.
this time last year I sent out a newsletter reviewing recent developments
in the understanding of autism. A study published in April, 2005 suggested
that children who develop autism have a genetic trait which lowers their
ability to inactivate toxic substances in their bodies. They were more
susceptible to injury from toxic exposures.
new study reported on in the May 30, 2006 issue of New Scientist takes
this a step further.
magazine reports that urine samples from French children show a link between
autism and heavy metals and dangle the possibility that the drugs used
to treat heavy metal poisoning might be useful in treating autism. [i]
sample obtained from autistic children contained high levels of chemicals
called porphyrins which are precursors to hemoglobin. Heavy metals block
hemoglobin production causing higher than expected amounts of porphyrin
to accumulate and show up in the urine. The concentrations of one molecule,
coproporphyrin, were 2.6 times higher in autistic children as in controls.
autism is linked isn't a totally new idea of course. An ongoing debate
has raged for years over the idea that autism is triggered by the mercury
used as a preservative in vaccinations. A hypothesis proposed in October,
2005 suggested that the mercury in the vaccines, although a small quantity,
was enough to inhibit the action of the enzyme methionine synthetase in
genetically susceptible individuals enough to cause changes in brain development.
International Journal of Toxicology reported in 2003 that infants with
autism had difficulty excreting mercury compared to other children. Researchers
had compared mercury levels in hair samples from healthy and autistic
children and found almost seven times the amount of mercury was being
excreted by the healthy kids. [iii]
recent New Scientist article says that normal porphyrin levels can be
restored through chelation in the autistic children but does not report
whether it affected their mental function. In recent years a good number
of anecdotal reports have circulated regarding the benefit of heavy metal
chelation therapy for autistic children yet I have not yet seen a well
controlled study of this therapy published. Given the current theories
and data though we should expect such a study in the near future.
Mercury and autism: accelerating evidence?
J , Naumann
J , Schneider
R , Walach
H , Haley
Institute for Environmental Medicine and Hospital Epidemiology, University
Hospital Freiburg , Germany . firstname.lastname@example.org
The causes of autism and neurodevelopmental disorders are unknown. Genetic
and environmental risk factors seem to be involved. Because of an observed
increase in autism in the last decades, which parallels cumulative mercury
exposure, it was proposed that autism may be in part caused by mercury.
We review the evidence for this proposal. Several epidemiological studies
failed to find a correlation between mercury exposure through thimerosal,
a preservative used in vaccines, and the risk of autism. Recently, it
was found that autistic children had a higher mercury exposure during
pregnancy due to maternal dental amalgam and thimerosal-containing immunoglobulin
shots. It was hypothesized that children with autism have a decreased
detoxification capacity due to genetic polymorphism. In vitro, mercury
and thimerosal in levels found several days after vaccination inhibit
methionine synthetase (MS) by 50%. Normal function of MS is crucial in
biochemical steps necessary for brain development, attention and production
of glutathione, an important antioxidative and detoxifying agent. Repetitive
doses of thimerosal leads to neurobehavioral deteriorations in autoimmune
susceptible mice, increased oxidative stress and decreased intracellular
levels of glutathione in vitro. Subsequently, autistic children have significantly
decreased level of reduced glutathione. Promising treatments of autism
involve detoxification of mercury, and supplementation of deficient metabolites.
Reduced levels of mercury in first baby haircuts
of autistic children.
AS , Blaxill
MF , Haley
SafeMinds, Cambridge , Massachusetts , USA .
Reported rates of autism have increased sharply in the United States and
the United Kingdom . One possible factor underlying these increases is
increased exposure to mercury through thimerosal-containing vaccines,
but vaccine exposures need to be evaluated in the context of cumulative
exposures during gestation and early infancy. Differential rates of postnatal
mercury elimination may explain why similar gestational and infant exposures
produce variable neurological effects. First baby haircut samples were
obtained from 94 children diagnosed with autism using Diagnostic and Statistical
Manual of Mental Disorders, 4th edition (DSM IV) criteria and 45 age-
and gender-matched controls. Information on diet, dental amalgam fillings,
vaccine history, Rho D immunoglobulin administration, and autism symptom
severity was collected through a maternal survey questionnaire and clinical
observation. Hair mercury levels in the autistic group were 0.47 ppm versus
3.63 ppm in controls, a significant difference. The mothers in the autistic
group had significantly higher levels of mercury exposure through Rho
D immunoglobulin injections and amalgam fillings than control mothers.
Within the autistic group, hair mercury levels varied significantly across
mildly, moderately, and severely autistic children, with mean group levels
of 0.79, 0.46, and 0.21 ppm, respectively. Hair mercury levels among controls
were significantly correlated with the number of the mothers' amalgam
fillings and their fish consumption as well as exposure to mercury through
childhood vaccines, correlations that were absent in the autistic group.
Hair excretion patterns among autistic infants were significantly reduced
relative to control. These data cast doubt on the efficacy of traditional
hair analysis as a measure of total mercury exposure in a subset of the
population. In light of the biological plausibility of mercury's role
in neurodevelopmental disorders, the present study provides further insight
into one possible mechanism by which early mercury exposures could increase
the risk of autism.