Differences in exposure to certain metals and nutrients like lead and zinc in the womb and in early childhood may affect a child’s risk of developing autism spectrum disorder (ASD), researchers say.
“Much of the research so far has identified genetic factors that cannot be changed,” said Dr. Manish Arora of the Icahn School of Medicine at Mount Sinai in New York.“Our study is an important step towards understanding modifiable risk factors such as exposure to environmental pollutants and dietary deficiencies,” he told Reuters Health by email, “and the most sensitive time periods when these exposures are harmful.”However, he stressed, “it is too early to make clinical recommendations.”
Arora and colleagues analyzed baby teeth from 16 pairs of identical and fraternal twins in Sweden, with at least one sibling who had an ASD diagnosis by the time they were about 18 years old. For comparison, they also analyzed baby teeth from 22 twin pairs who were developing normally.A new tooth layer is formed every week or so during fetal development and childhood. Each new layer is unique, and together, over time, they provide a record of exposure to various chemicals.
“Teeth are like 'biologic hard drives' - information is constantly being captured in their growth rings as teeth grow, starting in prenatal development,” Arora said by email. “By uncovering information from teeth, we can reconstruct what an individual experienced in utero and in childhood.”The team found significant differences in metal uptake between twins with ASD and their healthy siblings at certain points in development, they report in Nature Communications.
In late pregnancy and the first few months after birth, for example, the teeth of children with ASD showed a higher uptake of lead - a brain toxin - and a lower uptake of essential nutrients manganese and zinc.What’s more, three months after birth, the amount of toxic metals in teeth could predict the severity of ASD at ages 8 to 10 years.The authors note that the timing of unusually high or low uptake was different for each of the elements examined in the teeth.
In addition, the researchers don’t know if differences in the amount of toxic metals and nutrients in the teeth are due to how much a fetus or child is exposed to, or to differences in how they absorb and process these substances.The researchers also cannot say whether the disrupted uptake of these substances at particular stages of late fetal and early newborn development is a cause or an effect of autism. They suggest that these alterations likely involve multiple disruptions in the way metal uptake is regulated.
“It is important to remember that there is a long way to go before the results of this study can be useful to families and individual patients. More research is needed so that we can understand how nutrients, environmental toxins and genes interplay and lead to the development of autism,” said study coauthor Abraham Reichenberg, also with Icahn School of Medicine at Mount Sinai.
“Our genes and the genes of our babies are vulnerable to our ways of living,” Dr. Eric Butter, who wasn’t involved in the research, told Reuters Health by email. “What we eat, the air we breathe, and the things we do can change the way our genes work,” Butter, who is director of the Child Development Center and Pediatric Psychology/Neuropsychology at Nationwide Children’s Hospital in Columbus, Ohio, told Reuters Health by email.
The current study is helping researchers understand the “complicated relationships” between genes, toxic metals and nutrients, and how they may affect babies’ brains, Butter said.But the study “is not saying anything about the metal exposures and vaccine controversies that have plagued the autism community,” he cautioned.
“As in many of the best scientific advances in our field, this study opens many more important questions to be answered,” Butter said.