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Environmental Factor, September 2012

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Former NIEHS trainee identifies potential risk factor for autism subgroup

By Carol Kelly

Amy Kalkbrenner, Ph.D.

In addition to conducting research into environmental chemicals that contribute to neurodevelopmental disorders, Kalkbrenner teaches epidemiology at the Joseph J. Zilber School of Public Health at UWM. (Photo courtesy of Amy Kalkbrenner)

Children born to mothers who smoked during pregnancy have about a 25 percent increased risk for high-functioning autism, according to a recent study by Amy Kalkbrenner, Ph.D., a former NIEHS predoctoral and postdoctoral training grant recipient, and current assistant professor of epidemiology at the University of Wisconsin-Milwaukee (UWM).

In research funded in part by NIEHS, Kalkbrenner and her colleagues examined data on maternal smoking from birth certificates of nearly 634,000 children in 11 states. Using appropriate controls for social and demographic confounding factors, the birth certificate data was compared with data obtained from the Centers for Disease Control and Prevention Autism and Developmental Disabilities Monitoring Network on 3,315 children, aged 8 and under, who were diagnosed with an autism spectrum disorder (ASD). About 11 percent of the children with an autism spectrum disorder had mothers who smoked during pregnancy.

The large, population-based study found an association between maternal smoking and a subgroup of children with higher-functioning ASD, but it did not find an association with more severe forms of ASD. With the spectrum of autism disorders estimated to occur in 1 in 88 children nationally, understanding risk factors for different types of ASD is essential. This study is important because it shows that responses to environmental toxins may differ by children’s subtypes of autism, according to Kalkbrenner. 

Tobacco compounds and neurodevelopmental disorders

A wide variety of cognitive, achievement, and behavioral deficits have been identified in the children of women who smoked during pregnancy. Cigarette smoke contains more than 1,000 different compounds, but the two suspected of causing harmful effects on a developing fetus are carbon monoxide and nicotine.

"There are many potential biological pathways through which tobacco can harm the developing baby," said Kalkbrenner.

The identification of important environmental chemicals that are contributing to neurodevelopmental disorders is the basis of Kalkbrenner’s ongoing work. Her research focus areas include the environmental determinants of autism, disparities in autism diagnosis, measurement of exposure to pollutants like tobacco smoke and bisphenol A, and neurodevelopmental impacts of air pollutant exposures.

Citation: Kalkbrenner AE, Braun JM, Durkin MS, Maenner MJ, Cunniff C, Lee LC, Pettygrove S, Nicholas JS, Daniels JL. 2012. Maternal smoking during pregnancy and the prevalence of autism spectrum disorders, using data from the Autism and Developmental Disabilities Monitoring Network. Environ Health Perspect 120(7):1042-1048.

(Carol Kelly is a research and communication specialist with MDB Inc., a contractor for the NIEHS Division of Extramural Research and Training.)

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