When U.S. children who possess a variant gene are exposed to second-hand smoke in their homes, they are at a substantially greater risk for developing respiratory illnesses that lead to school absences.
The findings are reported in the second issue of the December 2005 American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
As part of the California-based Child Health Study, Frank D. Gilliland, M.D., Ph.D., of the Keck School of Medicine at the University of Southern California in Los Angeles, and eight associates analyzed 1,351 fourth grade students attending elementary school in southern California.
The researchers performed DNA analysis of cells from each child's cheek (buccal cells) and examined all participants' school absence reports. They found that genetic susceptibility caused by a variant genotype called "tumor necrosis factor 308A" influences the risk of respiratory-related school absences due to second-hand smoke.
Genotyping showed that 24 percent (324) of the fourth graders possessed one or more copies of the problem-causing variant.
According to baseline questionnaires completed by the children's parents, 20 percent had been exposed to second-hand smoke at home. Of those, 6 percent lived with one or more smokers.
Such exposure rates resulted in a 51 percent greater risk of lower respiratory illness compared with those who were not exposed. The researchers qualify this finding by noting that approximately 15 percent of the children involved in the study had physician-diagnosed asthma, which was associated with a 50 percent increase in risk for illness-related school absences.