Autism Speaks, Science, Latest Research

I. Hertz-Picciotto
Public Health Sciences and the M.I.N.D. Institute, University of California at Davis, Dept PHS, Davis, CA 95616

I. N. Pessah
3 Department of Veterinary Molecular Biosciences, University of California at Davis, M.I.N.D. Institute, One Shields Avenue, Davis, CA 95616

R. Hansen
Pediatrics and the M.I.N.D. Institute, University of California at Davis, 2825, 50th Street, Sacramento, CA 95817

P. Krakowiak
M.I.N.D. Institute, University of California at Davis, 2825 50th Street, Sacramento, CA 95817

Abstract
Background: Pesticides affect a number of targets in the CNS, and cross the placenta. One previous report suggests a link between maternal residential proximity to commercial organochlorine pesticide exposure during early prenatal life and the risk of autism. That study did not evaluate individual exposures to household pesticides.

Objectives: To examine household pesticide use during the prenatal period or early postnatal period in relation to autism.

Methods: Participants were from the CHARGE (Childhood Autism Risks from Genetics and the Environment study, a large population-based case-control study in California. Autism spectrum disorders were confirmed using the ADI and ADOS. Mothers were extensively interviewed regarding demographics, lifestyle, and prenatal and early postnatal exposures of the child. Questions addressed use of numerous household products, including insecticides for flies and ants, pet shampoos, and weed control products. Interview data were available for 333 ASD cases and 198 confirmed typically developing controls. Logistic regression models were adjusted for family socioeconomic status. An index exposure period was defined as three months prior to conception through the child's first year of life.

Results: Mothers of ASD children were twice as likely to report using pet shampoos for fleas or ticks during the index period as compared with control mothers: adjusted Odds Ratio (aOR) = 2.0, 95% Confidence Interval (CI) = [1.2, 3.6]. When examined by trimester, the strongest association was during the second trimester: aOR = 2.6, 95% CI = [1.3, 6.0].

Conclusions: The higher prevalence of self-reported use of pet shampoos by CHARGE study mothers of children with ASD could be due to reporting bias, although many other products did not show differences. Pyrethrins have largely replaced organophosphates for flea control, but early life exposure to pyrethrins has been shown to compromise the blood-brain barrier in rodents, raising concern about prenatal and early postnatal exposures.

Lay Abstract

Many pesticides commonly used in households are designed to target the central nervous system of insects, rodents or other species. This study focused on household pesticide use in relation to autism. Participants were from the Childhood Autism Risks from Genetics and the Environment (CHARGE) study, a large population-based case-control study in California. Cases were children aged 2-5 years with autism or an autism spectrum disorder. Controls were in the same age range, without autism or developmental delay, and were matched on sex and region of California. Families came to the M.I.N.D. Institute clinic at UC Davis where trained staff confirmed the diagnosis in cases, and ruled out developmental delay or disorders in controls. Through an extensive telephone interview with the mother, a trained staff person collected information on a wide range of exposures, including household products such as insecticides for flies and ants, pet shampoos, and weed control products. Interview data were available for 333 confirmed ASD cases and 198 confirmed typically developing controls. The exposure period examined was from three months prior to conception until 1 year of age.

Mothers of ASD children were twice as likely to report using pet shampoos for fleas or ticks during the exposure period as compared with control mothers. The strongest association was during the second trimester, but risk was elevated for use in other time windows as well.

Because this study collected data retrospectively, it is possible that mothers of typically developing children tended to forget about their use of pesticides around the home, which could have biased the results. Nonetheless, the higher self-reported use of pet shampoos by mothers of children with ASD raises concern about the safety of these products. The principal active ingredients in pet shampoos today are pyrethrins, along with piperonyl butoxide, which enhances the toxicity of pyrethrins. Although pyrethrin-based products are advertised as being very safe, pyrethrins can cause death of neurons and in rodent experiments have been shown to compromise the blood-brain barrier when administered in early life. Recent studies suggest that these compounds are now pervasive in homes in the U.S.