An article published in Nature Communications suggests that autism may be linked to exposure to lead, as well as zinc and manganese deficiencies, during the mother's pregnancy and immediately after birth. However, autism may not be connected to the exposure itself, but to the manner in which individual organisms process these metals.
The article details a study conducted by U.S. and Swedish researchers led by Manish Arora, from the NYC Icahn School of Medicine at Mount Sinai, analyzing the teeth of a small pool of twins for exposure to various elements.
It is not the first time that the correlation between metal exposure and autism spectrum disorder (ASD) has been noted. Early childhood exposure "to toxic metals and deficiencies of nutritional elements have been linked with several adverse developmental outcomes frequently associated with ASD, including intellectual disability, and language, attentional and behavioral problems", the authors note. However, it is the first time that naturally-shed teeth were used to observe which metals were involved and when the exposure occurred.
The conclusions of the study were clear: "When comparing ASD discordant twins with non-ASD control twin pairs, we found that lead levels were consistently higher in ASD cases than their non-ASD co-twins". Also, manganese and zinc levels were consistently lower in the ASD twins.
Metal exposure in early infancy also predicts the severity of the ASD. High lead exposure, for instance, was linked to severe autism. However, the mechanism is unclear, and it remains to be seen whether these metals actually cause autism or are merely improperly processed by the ASD individual. Since the individuals studied were part of twin sets, some of which contained two ASD individuals, others containing only one ASD individual, the inference may be drawn that the culprit is the metabolization of lead, zinc, and manganese in certain individuals.
Much additional work is necessary to answer these questions; however, it is a very important step forward that needs to be replicated and expanded.