by Julie Fidler, Natural Society:
Researchers are constantly studying and learning more about autism spectrum disorder (ASD), but they have yet to be able to pinpoint specific causes. The origins of the disorder seem to be based in genetics and environmental factors. Now a study funded by the National Institute of Environmental Health and Sciences (NIEHS) seems to suggest that exposure to heavy metals could be one of the environmental triggers of autism. 
The researchers behind the study found that the baby teeth of children with autism contain more lead and fewer vital nutrients, including manganese and zinc, compared to the teeth of children without the developmental condition.
Cindy Lawler, Ph.D., head of the NIEHS Genes, Environment, and Health Branch, said:
“We think autism begins very early, most likely in the womb, and research suggests that our environment can increase a child’s risk. But by the time children are diagnosed at age 3 or 4, it’s hard to go back and know what the moms were exposed to. With baby teeth, we can actually do that.” 
The study is the work of researchers from the Icahn School of Medicine at Mount Sinai Hospital. It involved 32 sets of twins recruited from a national database of twins in Sweden, and was intended to see whether levels of lead and other metals correlated with an increased risk of autism.