Being exposed to lead while in the womb or just after being born could increase a child’s chances of becoming autistic, scientists have said.
Lead exposure has previously been linked to cognitive problems, with some scientists accusing leaded petrol of having lowered national IQ levels.
Now researchers have looked to see what effect, if any, it and other elements have on the risk of autism. They studied 13 pairs of twins: in six of them both children were autistic and in the seven others only one was. They then compared them with 19 pairs of twins where neither child was autistic.
By analysing their baby teeth, which grow layer by layer, the researchers were able to measure their exposure to different elements throughout pregnancy and early development.
Manish Arora, from Mount Sinai institute in New York, described the teeth as “like a biological hard drive”. “We are able to go back in time for children who had autism, and their siblings, and see when did this difference start and what are the exact chemicals involved.”
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The scientists found that the autistic children generally had higher levels of lead just after birth. Their levels of manganese and zinc before and after birth, and zinc after birth were also lower than in non-autistic children.
Avraham Reichenberg, from the Icahn School of Medicine at Mount Sinai institute, one of the researchers, said that although there was clear evidence of a genetic component to autism, the study also helped to identify environmental factors.
He argued that the research could “help us uncover the root causes of autism, and support the development of effective interventions and therapies”. In particular, the role of zinc and manganese could be important.
Dorothy Bishop, professor of developmental neuropsychology at the University of Oxford, said the study was ingenious but interpreting it was difficult. In particular, the different deposition of metals in the babies’ teeth may not be because of exposure differences, but how their bodies dealt with them.
“The odd feature is that evidence for differences in metal uptake in those with autism came from analysis of features of teeth that are laid down prenatally: so you might expect both twins to have similar profiles, since they are together in the same uterus,” she said.
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“This study, then, does not suggest that different exposure to toxic metals in pregnancy causes autism; rather that there may be differences between foetuses in how the developing body responds to toxic metals.”
Jon Spiers, chief executive of the autism research charity Autistica, said that at least the work suggested routes for further research. “This study highlights the need for more research to tease out the poorly understood links between genetics and the environment. Although this study observed differences in exposure between those with autism and those without, it could not demonstrate that toxic metals were a cause of autism.”
Analysis
Autism is indisputably genetic. If your sibling has it, your chance of having it is raised ten-fold. If that sibling is an identical twin, your chance of also being autistic rises to 70 per cent (Tom Whipple writes).
But this isn’t the only answer, as some identical twins have different diagnoses. Researchers have, therefore, started to look at environmental influences before and just after birth.
In one study, children born in a house near a busy road were twice as likely to develop autism. In another, those with a particular genetic make up had an even higher risk. From this we can deduce that it is never just genetics or just environment but a complex interplay of the two.