Can prenatal exposure to pesticides cause autism?
According to the U.S. Centers for Disease Control and Prevention, about 1 in 68 children born in the U.S. are diagnosed with an autism spectrum disorder, or ASD. While the precise cause of ASD is not known, scientists believe that the condition develops as a result of the combination of several factors that are biological, genetic and environmental in nature. These factors may include genes, the use of certain medications during gestation and advanced parental age.
While some of these variables are not modifiable, parents do have control over whether they expose themselves to certain environmental toxins. This becomes a matter of identifying the toxins that increase the risk of ASD and figuring out how to reduce exposure. One team of scientists from the University of California, Davis Health System questioned whether pesticides could increase the risk of children being born with ASD, as published in the journal Environmental Health Perspectives.
'The message is very clear'
To investigate the possible link between prenatal exposure to pesticides and ASD in children, the authors of the study analyzed data collected for the Northern California-based Childhood Risk of Autism from Genetics and the Environment project, which included about 1,000 participating families with autistic children between the ages of 2 and 5 years. Specifically, the researchers collected information on where the parents lived during the pre-conception and gestational periods. This information was then plotted against a map showing sites of agricultural application of three classes of pesticides:
- Carbamates, which, according to the Merck Veterinary Manual, inhibits acetylcholinesterase at nerve synapses and neuromuscular junctions.
- Organophosphates, which act similarly to carbamates.
- Pyrethroids, which, according to Environmental Health Perspectives, alter the permeability of sodium ion channels in nerve cells.
Results showed that about one-third of study participants lived within 1.75 kilometers of pesticide application sites. Furthermore, the link between ASD and proximity to pesticides decreased as the addresses grew distant. This may be explained by the fact that all three classes of pesticides are neurotoxic.
"This study validates the results of earlier research that has reported associations between having a child with autism and prenatal exposure to agricultural chemicals in California," lead study author Janie Shelton, who now consults with the United Nations, said in a statement. "While we still must investigate whether certain sub-groups are more vulnerable to exposures to these compounds than others, the message is very clear: Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible."
Ultimately, Shelton and principal investigator Irva Hertz-Picciotto concluded that scientists need to find more effective ways to minimize exposure to pesticides during gestation.
"We need to open up a dialogue about how this can be done, at both a societal and individual level," Hertz-Picciotto said in a statement. "If it were my family, I would not want to live close to where heavy pesticides are being applied."
What are the signs of ASD?
According to the CDC, individuals who have ASD typically have a lot of trouble communicating with those around them and may display problematic behaviors. Among the signs of ASD are:
- Having trouble relating to others
- Having no interest in interacting with others
- Trouble adapting to changes in routine
- Avoiding eye contact
- Preference for being alone
- Not looking at objects when someone points them out
- Not pointing at objects of interest
- Having trouble expressing needs through words or motions
- Unusual reactions to sensory stimulation
- Loss of skills that were once had, including a shrinking vocabulary
There is no cure for ASD. However, if parents and paediatricians identify the signs of ASD and diagnose the condition early enough, children may benefit from early intervention programs that promote developmental skills.
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