Interesting new study! Researchers analyzed baby teeth among twins - sets of twins where both are healthy, and sets of twins where one has autism spectrum disorder (ASD), but not the other twin (the control). They found that in the children that developed ASD, the teeth revealed that during the second and third trimester and 30 weeks after birth they had higher levels of lead (which is a neurotoxin) and lower levels of the essential nutrients manganese and zinc. There were also differences between ASD and controls in levels of other elements including tin, strontium and chromium - but each of these elements differed the most between the ASD and control twin at different points of time.
How many people know that during fetal and childhood development, a new tooth layer is formed every week or so in the developing baby, which leaves an "imprint" in the tooth layer of the chemicals exposed to? So there's a chronological record of exposure - similar to using growth rings on a tree to find out the tree's growth history. A laser removed a tiny bit of the tooth dentine layer and then it was analyzed for various metals (see the illustration below).
Now studies are needed to determine whether the differences in the amount of lead and metals are due to differences in how much a fetus or baby is exposed to them, or whether it occurs because of a genetic difference in how a baby takes in and handles these metals and nutrients. And, of course, other studies suggest that other environmental exposures (e.g., pesticides) may also play a part in ASD development. From Science Daily:
Using evidence found in baby teeth, researchers from The Senator Frank R. Lautenberg Environmental Health Sciences Laboratory and The Seaver Autism Center for Research and Treatment at Mount Sinai found that differences in the uptake of multiple toxic and essential elements over the second and third trimesters and early postnatal periods are associated with the risk of developing autism spectrum disorders (ASD), according to a study published June 1 in the journal Nature Communications.
The critical developmental windows for the observed discrepancies varied for each element, suggesting that systemic dysregulation of environmental pollutants and dietary elements may serve an important role in ASD. In addition to identifying specific environmental factors that influence risk, the study also pinpointed developmental time periods when elemental dysregulation poses the biggest risk for autism later in life.
According to the U.S. Centers for Disease Control and Prevention, ASD occurs in 1 of every 68 children in the United States. The exact causes are unknown, but previous research indicates that both environmental and genetic causes are likely involved. While the genetic component has been intensively studied, specific environmental factors and the stages of life when such exposures may have the biggest impact on the risk of developing autism are poorly understood. Previous research indicates that fetal and early childhood exposure to toxic metals and deficiencies of nutritional elements are linked with several adverse developmental outcomes, including intellectual disability and language, attentional, and behavioral problems.
"We found significant divergences in metal uptake between ASD-affected children and their healthy siblings, but only during discrete developmental periods," said Manish Arora, PhD, BDS, MPH, Director of Exposure Biology at the Senator Frank Lautenberg Environmental Health Sciences Laboratory at Mount Sinai and Vice Chair and Associate Professor in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai. "Specifically, the siblings with ASD had higher uptake of the neurotoxin lead, and reduced uptake of the essential elements manganese and zinc, during late pregnancy and the first few months after birth, as evidenced through analysis of their baby teeth. Furthermore, metal levels at three months after birth were shown to be predictive of the severity of ASD eight to ten years later in life."
To determine the effects that the timing, amount, and subsequent absorption of toxins and nutrients have on ASD, Mount Sinai researchers used validated tooth-matrix biomarkers to analyze baby teeth collected from pairs of identical and non-identical twins, of which at least one had a diagnosis of ASD. They also analyzed teeth from pairs of normally developing twins that served as the study control group. During fetal and childhood development, a new tooth layer is formed every week or so, leaving an "imprint" of the micro chemical composition from each unique layer, which provides a chronological record of exposure. The team at the Lautenberg Laboratory used lasers to reconstruct these past exposures along incremental markings, similar to using growth rings on a tree to determine the tree's growth history. [Original study.]
Cross-section of tooth showing laser removal of the dentine layer (in tan), for analysis of metal content. Credit: J. Gregory, Copyright Mount Sinai Health System, 2017