Children
who develop autism may do so because they have problems processing
the toxic metal mercury, researchers have suggested.
Autism
experts want to see more research into mercury levels.
US
researchers looked at mercury levels in the baby hair of children
who later developed autism, a developmental disability that
affects how a person communicates and interacts with other
people.
They were found to have far lower levels of mercury than children
who did not have the condition, according to New Scientist
magazine.
The researchers say this could be because autistic children's
bodies cannot make use of metals such as mercury properly,
or because they have trouble excreting the metal from their
body.
"The
findings of this study are intriguing"
National
Autism Society spokeswoman
Mercury
is suspected by some to be a cause of autism.
A group of parents in the US and Canada are suing health authorities
because they believe thimerosal, a mercury-based preservative
used in vaccines, could have caused their children's autism.
The MMR vaccine, which some parents fear is linked to autism,
does not contain thimerosal.
Baby hair
Experts are divided over whether there could be a link.
Some say more studies need to be carried out before a link
between mercury and autism can be confirmed.
But others, such as Louisiana-based Dr Amy Holmes, who carried
out this latest research, believe there is a causal link.
Dr Holmes obtained baby hair cuttings taken which had been
taken when children were around 18 months old.
She analysed mercury levels in cuttings from 94 autistic children
and 45 other children
The average level of mercury in baby hair of children later
diagnosed as autistic was 0.47 parts per million, compared
to 3.63 per million in the other children.
The more severe the children's autism, the lower the mercury
levels found.
Deficiencies
Most of the mercury came from the children's mothers in the
form of fillings, injections containing the thimerosal, or
through eating a lot of fish.
In the group of non-autistic children, mercury levels rose
in line with their mother's exposure.
But levels in the baby hair of the autistic children were
low even when their mother's exposure was high.
The researchers say one explanation could be that autistic
children's bodies are unable to make use of metals properly,
so they could also be deficient in metals which are needed
for brain development such as zinc, iron and copper.
Alternatively, they suggest some children might have problems
excreting mercury.
Most of the metal is excreted through urine and faeces.
However the researchers suggest that the lack of mercury in
the children's hair could be due to the metal being retained
in cells, rather than getting into the blood.
'Logical leap'
Some experts say the link is plausible.
Professor Simon Baron Cohen of Cambridge University, said:
"This kind of gene-environment interaction is not incompatible
with the known heritability [genetic factors] of autism.
"If these results hold up, metal studies on the brain could
be revealing."
But Dr Emmanuel Dicicco-Bloom, a child neurologist at the
Robert Wood Johnson Medical School in New York warn more evidence
is needed before a link between mercury processing and autism
can be confirmed.
He told New Scientist it was a big logical leap, not justified
by the evidence.
A spokeswoman for the UK's National Autistic Society told
BBC News Online: "The findings of this study are intriguing
and we would encourage further investigation into what factors
might be causing this complex disorder."
The research is due to be published in the International Journal
of Toxicology in September.
Autism
experts want to see more research into mercury levels.
