What is the role of toxins in the etiology of autism spectrum disorder (ASD)?

Updated: Sep 30, 2019
  • Author: James Robert Brasic, MD, MPH; Chief Editor: Caroly Pataki, MD  more...
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Exposures to toxins, chemicals, poisons, and other substances have been hypothesized to cause autism. Although anecdotal case reports suggest that such exposures may play a role in isolated cases of autistic disorder, a causative role for toxins in the development of autism in general has not been demonstrated.

Roberts et al [78] and Samson [79] have reported an association between exposure to the organochlorine pesticides dicofol and endosulfan during the first trimester of pregnancy and the subsequent development of autism spectrum disorder in children. Potential mothers can wisely be advised to avoid exposure to organochlorine pesticides.

In parts of the world, exposure to specific toxins may influence local autism rates. For example, the high incidence of autism in areas of Japan has been hypothesized to be due to a toxic effect of certain fish. Although toxins may play a role in the development of isolated cases of autism in Japan, they have not been proved to be generally causative of autism there. Another possible explanation for the high autism rates in Japan is the excellent training of Japanese clinicians; low rates elsewhere may reflect the limited abilities of clinicians to diagnose autism.

Some studies have documented associations between autism and air pollution. One, from North Carolina found a link between exposure to traffic-related air pollution, particularly during the third trimester, to the development of autism in offspring. These results add to the evidence already provided by previous studies conducted in California. [80]

Another study of children living in counties in Pennsylvania found that children with autism were 1.4 to two times more likely to have been exposed to higher levels of air pollution, especially the toxins styrene and chromium, during pregnancy and the first 2 years of life than children without the disorder. [81] Cyanide, methylene chloride, methanol, and arsenic were also linked to increased risk of autism. [82]  

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