Washington, May 19: Smoking during pregnancy by mothers or grandmothers puts the child at an increased risk of developing asthma, but the root cause behind this was so far not well understood. Now, a new study has found that changes in a process called DNA methylation that occurs before birth, can be a valid reason.

DNA methylation is a process that can alter a gene''s usual function. In this case, researchers observed DNA methylation-related changes in the AXL gene in children exposed to maternal smoking in utero and found that the change that reduced the immune response.

"We found that children exposed to maternal smoking in utero had a 2.3 percent increase in DNA methylation in AXL," said Carrie Breton, ScD, assistant professor of preventive medicine at The Keck School of Medicine of the University of Southern California (USC) in Los Angeles.

Using a detailed questionnaire, the researchers targeted the mothers and grandmothers of 173 children participating in the Early Asthma Risk Factors Study (EARS), a study within the larger California Children''s Health Study, and assessed their smoking habits during pregnancy.

Dr. Breton said that the results of the study indicate the need for a greater understanding of the effects environmental factors have on epigenetic.

" Any environmentally-induced epigenetic changes will have greater impact on gene expression and function. In utero and early life exposures are likely to be important, given what we know about timing during development when epigenetic marks are established," she added.

"We are interested in further characterizing the pattern of epigenetic marks across this gene and whether there is a widespread response to both maternal smoking exposure and air pollution exposure in utero," Dr. Breton said.

The study will be presented at the ATS 2011 International Conference. (ANI)