June 5, 2017Neurology
Prior studies relating toxic metals and essential nutrients to autism have faced key limitations, such as estimating exposure based on blood levels after autism diagnosis rather than before, or not being able to control for differences that could be due to genetic factors. Now, according to an article published online in the journal Nature Communications (1 June 2017), baby teeth from children with autism have been shown to contain more toxic lead and less of the essential nutrients zinc and manganese, compared to teeth from children without autism. The study evaluated twins in order to control genetic influences and focus on possible environmental contributors to the disease. The findings suggest that differences in early-life exposure to metals, or more importantly how a child's body processes them, may affect the risk of autism. The differences in metal uptake between children with and without autism were especially notable during the months just before and after the children were born. The authors determined this by using lasers to map the growth rings in baby teeth generated during different developmental periods. Higher levels of lead were observed in children with autism throughout development, with the greatest disparity observed during the period following birth. The authors also observed lower uptake of manganese in children with autism, both before and after birth. The pattern was more complex for zinc. Children with autism had lower zinc levels earlier in the womb, but these levels then increased after birth, compared to children without autism. The authors noted that replication in larger studies is needed to confirm the connection between metal uptake and autism.
For the study, patterns of metal uptake were compared using teeth from 32 pairs of twins and 12 individual twins. The study then compared patterns in twins where only one had autism, as well as in twins where both or neither had autism. Results showed that smaller differences in the patterns of metal uptake occurred when both twins had autism, but that larger differences occurred in twins where only one sibling had autism. The findings build on prior research showing that exposure to toxic metals, such as lead, and deficiencies of essential nutrients, like manganese, may harm brain development while in the womb or during early childhood. Although manganese is an essential nutrient, it can also be toxic at high doses. Exposure to both lead and high levels of manganese has been associated with autism traits and severity.a