Pregnant women who are exposed to other people's cigarette smoke might be raising their fetuses' risk of developing cancer in childhood.
A study found that babies born to exposed mothers showed higher rates of a kind of genetic mutation in blood cells. This kind of mutation is caused by a particular enzyme, and it is often found in childhood leukemia and lymphoma.
Experts said it is the first time scientists have linked secondhand smoke to genetic mutations in a fetus. Prior research found elevated mutation rates in fetuses from women who themselves smoked during pregnancy.
The study doesn't show a direct link to cancer. In fact, the specific gene mutations it monitored are harmless because they occurred in a gene unrelated to cancer.
The findings only suggest that if a pregnant woman is exposed to cigarette smoke, the mutation-making enzyme might become more active in her fetus, raising the risk of hazardous mutations in cancer-related genes.
The study couldn't define how big a risk secondhand smoke might pose, but it's rare for children to get leukemia or lymphoma at all. Only about 3,000 new cases, mostly leukemia, are expected in the United States this year in children up to age 14.
The work was presented in the October issue of the journal Nature Medicine by Dr. Barry Finette, Dr. Richard Albertini and colleagues at the University of Vermont in Burlington.
It's an important finding that requires follow-up study, said Frederica Perera, director of Columbia University's Center for Children's Environmental Health. A fetus is ``exquisitely sensitive'' to exposure to many toxins, including those in tobacco smoke, because the defense systems present in adults are still developing, she said.
The study involved 24 newborns from nonsmoking mothers. Half were born to women who said they had been exposed to other people's smoke at home, at work or in both places. The other half were born to women who reported no such exposure.
The researchers inspected white cells in blood from the placenta. They looked for mutations in a gene called HPRT. This gene has nothing to do with cancer, but researchers used it as an indicator of how often particular kinds of mutations had occurred generally in the newborn.
The key finding pertained to a kind of genetic splicing carried out by an enzyme called V(D)J recombinase. Normally, the enzyme helps the immune system prepare to fight a variety of germs. But when the enzyme makes a mistake, it can set the stage for cancer.
The study found that HPRT mutations produced by the enzyme appeared at a higher rate in the smoke-exposed group, at 34 percent of all mutations counted vs. 20 percent. When researchers counted only mutations that deleted large chunks of genetic material, the difference was 67 percent vs. 30 percent.
Finette said he suspects substances in cigarette smoke make fetal DNA more vulnerable to mutations by the enzyme.
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