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Study Links Autism to Heavy-Metal Exposure

Offering new insight into the causes of autism, a government-funded study published Thursday looks at the metal content in baby teeth.

BETHESDA, Md. (CN) - Offering new insight into the causes of autism, a government-funded study published Thursday looks at the metal content in baby teeth.

Appearing this morning in the journal Nature Communications, the study found that the baby teeth of children with autism contained more toxic lead, and less of the essential nutrients zinc and manganese, than the teeth of children without autism.

The National Institute of Environmental Health Sciences, which is part of the National Institutes of Health, funded the study, which involved using lasers to map the growth rings in baby teeth generated during different developmental periods.

To control genetic influences and focus on the environmental factors that contribute to autism,

the researchers conducted their tests on 32 pairs of twins and 12 individual twins.

In the cases where both twins had autism, researchers found smaller differences in the patterns of metal uptake. There were larger differences in metal-uptake patterns, however, in cases where only one of the twins in a set had autism. Sets of twins where neither child had autism were also included in the study.

Researchers found that it was during the months just before and after the children with and without autism were born that the biggest differences in metal uptake were apparent.

“The researchers observed higher levels of lead in children with autism throughout development, with the greatest disparity observed during the period following birth,” a report on the study by the NIH says. “They also observed lower uptake of manganese in children with autism, both before and after birth. The pattern was more complex for zinc. Children with autism had lower zinc levels earlier in the womb, but these levels then increased after birth, compared to children without autism.”

To bolster the connection between metal uptake and autism, the researchers said larger studies must be undertaken to replicate their results.

Cindy Lawler, head of the NIEHS Genes, Environment, and Health Branch, noted that it is hard for researchers to determine environmental causes because children with autism are not usually diagnosed until they are 3 or 4 years old.

“With baby teeth, we can actually do that,” Lawler said, as quoted in the NIH report.

Manish Arora, an environmental scientist and dentist at the Icahn School of Medicine at Mount Sinai in New York, led the new study. While genetics and the environment play a role in autism, Arora said it has been difficult to determine the environmental exposures that increase risk.

“What is needed is a window into our fetal life,” Arora said, as quoted in the NIH report. “Unlike genes, our environment is constantly changing, and our body’s response to environmental stressors not only depends on just how much we were exposed to, but at what age we experienced that exposure.”

The NIH notes that the researchers studied naturally shed baby teeth, using lasers to extract precise layers of dentine, the hard substance beneath tooth enamel, for metal analysis.

Existing research has already tied lead exposure and nutrient deficiencies to brain-development issues in the womb or during early childhood.

“Although manganese is an essential nutrient, it can also be toxic at high doses,” the NIH report warns. “Exposure to both lead and high levels of manganese has been associated with autism traits and severity.”

David Balshaw, who heads the NIEHS Exposure, Response, and Technology Branch, noted that the baby-teeth analysis holds promise for studying other disorders, such as attention deficit hyperactivity disorder.

“There is growing excitement about the potential of baby teeth as a rich record of a child’s early life exposure to both helpful and harmful factors in the environment,” Balshaw said, as quoted in the NIH report.

Funding for the study also came from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and from the National Institute of Mental Health.

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