Asthma and other respiratory diseases have been linked to variations in the genes that control enzymes responsible for clearing harmful chemicals breathed into the body.
As part of the study researchers examined microsomal epoxide hydrolase (EPHX1) levels and genetic variations in gluathione S-transferase P1 (GSTP1), which are involved in clearing the body of toxins, including polyaromatic hydrocarbons from vehicle emissions, in more than 3000 schoolchildren who had been diagnosed with asthma.
The study found that children with very active EPHX1 were 1.5 times as likely to have asthma as those with low EPHX1 activity and if they also carried a variation of the GSTP1 gene, they were four times as likely to have asthma.
The study noted that proximity to road traffic pollution seemed to have a key role in triggering genetic susceptibility as children with very active EPHX1 and living within 75 metres of a main road were more than three times as likely to have asthma as those with relatively low EPHX1 levels while children with one or two variations in the GSTP1 gene, and who lived close to a major road, were up to nine times as likely to have asthma as those who lived further away.
The authors conclude that children with high EPHX1 activity, who carried genetic variants of GSTP1 were at greater risk of developing asthma but the risk appeared to be even greater in those who lived close to main roads and were exposed to road traffic pollution.
The findings of the study were published in the journal Thorax.