By Catherine Clabby
Autism researchers have a big problem that tiny baby teeth might help solve.
Evidence is rising that environmental exposures in the womb and after birth may explain some of the rise in autism diagnoses nationally, a count that now includes close to one out of every 68 kids.
But what toxins could be causing the trouble? When might exposure be most risky? To answer that, University of North Carolina, Chapel Hill researchers and others around the country are expanding their research to study milk teeth to find out.
Once valued only to lure Tooth Fairy “visits” to a child’s bedroom, deciduous teeth are actually biobanks. Because they begin forming during the embryonic stage of development, the structures absorb and store traces of many compounds — good and bad — that a fetus and later a newborn has contact with.
Technology developed at the Icahn School of Medicine at Mt. Sinai in New York uses a mix of lasers and chemical sensors to read what’s stored within layers of dentine, a hard substance shielded by tooth enamel. Just as tree rings do, new layers formed within these teeth every week or so place what was absorbed in chronological order.
That tool made possible a study published early this month revealing that the teeth of children with autism contain more toxic lead and lower levels of the essential nutrients zinc and manganese when compared to teeth lost by children without autism.
Using baby teeth as a novel biomarker of early life environmental exposure, researchers from the Lautenberg Environmental Health Science Lab and the Seaver Autism Center for Research and Treatment at Mount Sinai in New York City found ways to discover clues to the development of autism.
The differences detected in the study, funded by the National Institute of Environmental Health Sciences, were most pronounced in the layers of teeth formed before the children were born.
“This can really give you timing as well as amount of exposure,” said
Joseph Piven, director of the Carolina Institute for Developmental Disabilities
at UNC-Chapel Hill, whose research team is now collecting baby teeth from families enrolled in its studies of the younger siblings of children with autism.
A complicated puzzle
The cause of autism is a tough nut to crack because the disorder is really a group of disorders. Some people diagnosed with autism are brilliant, with bear-trap memories and rare talents. Others can be severely cognitively and developmentally impaired.
But no matter where they dwell along the spectrum, people with autism usually share three traits.
They have trouble communicating, whether that be speaking or understanding language. They miss social cues—including facial expressions—that most people read effortlessly. And they partake in repetitive behaviors, such as talking about just one topic or repeating gestures other people consider odd.
It’s certain that genetics contribute significantly to the abnormal brain development suspected to spur autism. If one identical twin has autism, for instance, the second almost always does.
But environmental exposures are also in play, with higher risk of developing autism now tied to exposure to auto exhaust, pesticides and even inflammation experienced by a pregnant woman during pregnancy.
Further complicating things, genetic variation can influence the scale of danger posed by some toxins. Children whose genetic makeup causes them to be more susceptible to the health effects of high levels of air pollution, for instance, are at greater risk for having the disorder.
Piven’s UNC team and its collaborators in the Infant Brain Imaging Study (IBIS) track how physical differences in the brains of children with autism relate to autistic-like behavior.
To try to capture both as they unfold, the team has scanned the brains and recorded the behavior of younger brothers and sisters of kids with autism for years. These siblings are at increased risk of having autism too, with one in five nationally likely to be diagnosed.
The UNC studies have documented that abnormal growth and other qualities in the brains of the siblings frequently predict by ages six and 12 months which of the children will be diagnosed with autism by age two. Early diagnosis of kids with autism is favored because even though children can’t be cured, many benefit from early treatment.
Studies of the siblings’ teeth, possible due to a collaboration with the Mt. Sinai researchers, will contribute more insight into those children’s environments, within and without the womb. “The idea is to collect the baby teeth of these kids to look at environmental exposures,” Piven said.
While teeth studies can’t convey all that children at risk have been exposed to, they can document a good bit, particularly metals, said Heather Volk, a public health scientist at Johns Hopkins University collaborating with Piven.
“It’s not just measuring exposures to metals that can be bad. They also look at exposures that are necessary for brain development that are lacking,” said Volk, whose research has linked exposure to vehicle air pollution during the first year of life to higher rates of autism.
“That’s the sort of information that can potentially open new avenues for prenatal care that promote healthy brains,” she said.