Study links factors in environment with autism
Scientists examined baby teeth from twins
Scientists analyzing mineral deposits in the baby teeth of twins, where one of whom had autism, found a discrepancy in heavy metals and nutrients. This discovery adds support to the argument that the environment, as much as genes, can lead to the disorder.
The teeth of the children with autism were found to have higher amounts of lead and lower levels of manganese — toxins known to contribute to attention and behavioral disorders — and an inconsistent absorption of zinc, a mineral essential to proper health and development.
The study was published Thursday in the journal Nature Communications and was conducted by researchers in the U.S. and Sweden with support from the National Institutes of Health.
The Centers for Disease Control and Prevention estimates that 1-in-68 children have autism spectrum disorder (ASD). Autism is about 4 1/2 times more common in boys than girls.
People with autism have difficulty interacting physically and emotionally with others and the world around them. Symptoms include a sensitivity to external stimuli, such as bright lights and loud sounds, which can produce anxiety or anxious behavior.
There is a growing prevalence of ASD and while scientists attribute the higher numbers to becoming more skilled at diagnosis, they also acknowledge that the increasing frequency is happening at greater rates than can be attributed to genes and increased diagnostics alone.
“I think there is consensus in the scientific community that the prevalence of autism is increasing and our genes don’t change so quickly,” said Manish Arora, an environmental scientist and dentist at the Icahn School of Medicine at Mount Sinai in New York and lead author of the study. “Essentially there are environmental drivers for autism that are interacting with our genetic makeup.”
Comparing identical and fraternal twins where one sibling had autism allowed scientists to control the genetic factors. Although finding the samples proved difficult enough in itself, Dr. Arora said.
The scientists worked from the Swedish Roots of Autism and ADHD Twin Study, which had been collecting samples from twins where one sibling is autistic.
The study included 32 complete twin pairs and 12 individuals from twin pairs whose sibling did not donate a tooth.
“So these are very rare and very precious samples,” Dr. Arora said.
Using advanced laser technology, the researchers were able to evaluate baby teeth much like rings of a tree are studied, Dr. Arora said, and were able to recreate the prenatal environment.
“We developed a method using lasers where we can start mapping the environment, but the environment even before they were born,” he said.
Researchers used a tooth-matrix biomarker to examine pre- and post-natal levels of certain minerals, including zinc, manganese and lead among the “growth rings in teeth,” which start to form beginning in the second trimester.
They found that the differences in the uptakes of the metals were most prominent during the periods just before and after birth.
“We think autism begins very early, most likely in the womb, and research suggests that our environment can increase a child’s risk,” said Cindy Lawler, head of the Genes, Environment, and Health Branch of the National Institute of Environmental Health Sciences. “But by the time children are diagnosed at age three or four, it’s hard to go back and know what the moms were exposed to. With baby teeth, we can actually do that.”