NEW YORK (Reuters Health) — Smoking during pregnancy is known to raise a child's future asthma risk, but children with a particular gene variation may be especially vulnerable, a study published last week suggests.Researchers found that among children followed from birth to age 10, those with a particular variant of a gene called IL1RN seemed particularly susceptible to the effects of maternal smoking during pregnancy. Compared with other children whose mothers smoked, they were four times more likely to develop asthma by the age of 10.

IL1RN is the gene for a protein called the interleukin-1 receptor antagonist, which has a strong anti-inflammatory action in the body. Theoretically, a change in the gene could reduce the effectiveness of the IL1RN protein and thereby contribute to the chronic airway inflammation that marks asthma.

The current study, published in the European Respiratory Journal, looked at whether certain variations in the IL1RN gene might make children more susceptible to the effects of their mothers' smoking.

It included 921 UK children who were assessed for asthma at ages one, two, four and 10, and had blood samples taken to see which IL1RN variant they carried. The researchers also collected information on each child's family history of allergies and asthma, mothers' smoking habits and other health factors.

Overall, the study found that among children whose mothers smoked during pregnancy, those who carried the least common form of IL1RN — found in about six percent of all the children — were more than four times as likely to develop asthma as those with other variants of the gene.

The gene variant alone, however, was not linked to a higher asthma risk; it only made a difference when the mother smoked.

So, no matter what influence genes may have, a central message from the findings is that protecting children from tobacco smoke can lower their asthma risk, according to study co-author Dr. Susan Ewart, a researcher at Michigan State University in East Lansing.

"It's really underscoring the importance of not smoking during or after pregnancy," Ewart told Reuters Health, noting that all of the children whose mothers smoked during pregnancy were also exposed to second hand smoke after birth. No mother said she'd smoked during pregnancy, then quit afterward.

IL1RN is only one of a number of genes that may play a role in asthma development, Ewart pointed out. The current findings, she said, highlight the fact that asthma, like many other chronic diseases, arises from a complex interaction of genes and environmental exposures.