(Beyond Pesticides, May 27, 2008) A population-based study looking at how genes and environmental factors interact shows that pet shampoos containing insecticides may trigger autism spectrum disorders (ASD), reports New Scientist. The study findings, presented at the International Meeting for Autism Research, show that mothers of children with an ASD are twice as likely to have used an insecticidal pet shampoo during the prenatal and/or postnatal period when compared to mothers of healthy children. The strongest association was during the second trimester of pregnancy. According to the researchers, pet shampoos often contain pyrethrins and previous animal research has found that pyrethrins are designed to target the central nervous system in insects, rodents and other species and can cause death of neurons and compromise the blood-brain barrier in early life.Examining participants in the Childhood Autism Risks from Genetics and the Environment (CHARGE) study, researchers from the University of California, Davis looked at 333 children with ASD and 198 healthy children between the ages of two and five, and their families. In-depth questionnaires and blood and urine samples were collected.
Isaac Pessah, Ph.D., a researcher involved in the study and professor in the Department of Molecular Biosciences, College of Veterinary Medicine at UC Davis, told the New Scientist, â€œAutism is associated with an imbalance between excitatory and inhibitory neurotransmitters within the brain, and one could hypothesize that children with an imbalance in this system may be more sensitive to the effects of pyrethrins.”
Autism, which is on the rise in both prevalence and incidence, is a complex developmental disorder that includes problems with social interaction and communication. The symptoms range from mild to very severe, appearing before the age of three and lasting throughout a personâ€™s life. Research has shown that people with autism have certain irregularities in several regions of the brain and/or have abnormal levels of serotonin or other neurotransmitters in the brain, suggesting that autism is associated with the disruption of normal brain development early in fetal development. It is increasingly recognized that autism likely is caused by a complex interplay of both genetic and environmental factors.
Many of the most commonly used pesticides are designed specifically as neurotoxins. The transmitter systems and hormone systems of humans are similar to those of the insects those insecticides are targeting, according to a study published in 2004 in Pediatrics. Researchers show that animal studies and residual effects in humans following acute intoxication suggest that organophosphates can be toxic to the developing brain at exposure levels below those inducing overt signs. A study published in 1998 also showed that organochlorine pesticides are a source of developmental neurotoxicity in humans. A study published in the October 2007 issue of Environmental Health Perspectives shows that children born to mothers living near agricultural fields where organochlorine pesticides were applied during their first trimester of pregnancy were six times more likely to have children with autism compared to mothers who did not live near the fields.