Tics are repeated twitches, movements or sounds that people are unable to control.

For the study, researchers analyzed data from more than 73,000 births in Denmark. The investigators found that children whose mothers smoked 10 or more cigarettes a day during pregnancy had a 66 percent increased risk of developing a chronic tic disorder.


Heavy smoking during pregnancy was also linked to a twofold to threefold increase in a child's risk for chronic tics in combination with other neuropsychiatric conditions, such as attention-deficit/hyperactivity disorder (ADHD).

"Identifying environmental causes for chronic tic disorders and related psychiatric conditions is important because if we know specific risk factors, we can develop more effective strategies for prevention," said senior study author Dr. Dorothy Grice. She is a professor of psychiatry at the Icahn School of Medicine at Mount Sinai in New York City.

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The study was published in the September issue of the Journal of the American Academy of Child and Adolescent Psychiatry.

Grice said the study findings suggest that exposure to nicotine may cause subtle changes in fetal brain development, although the study did not prove a cause-and-effect relationship. The next step is to understand how environmental factors exert their effects on risk, she noted.

"This will provide a window into the biological mechanisms that underlie these conditions. As we learn more about the neurobiological pathways that underlie a specific disorder, we will be better positioned to develop more specific and targeted treatments," Grice said in a journal news release.

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Maternal smoking is also linked to premature births and lower birth weights, which may increase the risk for behavior problems later on, the researchers pointed out.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more on Tourette syndrome.

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