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"We already know that protecting a baby from tobacco smoke is one of the best things a woman can do to give her child a healthy start in life," said study co-author Jean Golding of the University of Bristol. "Now we've found that not smoking during pregnancy could also give their future grandchildren a better start, too."
The study can't prove cause-and-effect, but one U.S. autism expert who reviewed the findings said the researchers' conclusion is not farfetched.
While the finding is new, "the mechanism by which it might be occurring has been a focus of study for half a decade," noted Alycia Halladay. She's chief science officer for the Autism Science Foundation.
Halladay believes that when a woman smokes in her pregnancy, this could affect the developing eggs of a female fetus in the womb. And that, in turn, might affect the odds that her daughter's children are at higher autism risk, she suggested.
In the new study, researchers analyzed data from more than 14,500 children born in the United Kingdom during the 1990s.
The study found that people with a maternal grandmother who smoked during her pregnancy had a 53 percent increased risk of developing autism.
The findings also showed that girls whose maternal grandmother smoked during pregnancy were 67 percent more likely to have autism-linked traits -- symptoms such as poor social communication skills and repetitive behaviors.
The researchers agreed with Halladay: Exposure to cigarette smoke while in the womb could affect a female's developing eggs, causing changes that may eventually affect the development of her own children.
Still, the study authors stressed that further investigation is needed to determine what those molecular changes might be, and to find out if the same associations occur in other groups of people.
Another U.S. autism expert said the findings were intriguing.
"There are innumerable reasons why people should not smoke," said Dr. Andrew Adesman. "This study provides more reason: women who smoke during pregnancy put their granddaughters at increased risk of an autism spectrum disorder."
But "the overall increase in risk related to smoking is somewhat modest," added Adesman. He is chief of developmental and behavioral pediatrics at Cohen Children's Medical Center, in New Hyde Park, N.Y.
"Although a woman's exposure to cigarette smoke prenatally appears to be linked decades later to autism spectrum disorder in her own offspring, women who smoke or who were themselves exposed to cigarette smoke prenatally should take some comfort in knowing that their risk of having a child with an autism spectrum disorder is still very low," Adesman said.
For her part, Halladay said it's typically been tough for scientists to assess how behaviors affect multiple generations of offspring, and so most of the research in this area "has been done in animal models."
But the U.K. database used in the new study "has the data to assess grandparental exposures," she believes.
Because the database the researchers drew on was so detailed, the researchers said they were able to rule out possible other factors that might account for the link.
Autism spectrum disorder affects about one in 68 children in the United States, with boys affected far more often than girls.
The study was published April 27 in the journal Scientific Reports.
-- Robert Preidt
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