(Ivanhoe Newswire) -- New research clarifies the link between a certain genetic variant and asthma in children.

Although the variant has been known to be associated with asthma in children, the new study shows it to be associated with asthma in children age 4 or younger. The results also show the risk of asthma associated with the variant is exacerbated by secondhand smoke.

Researchers tested 36 different variants in the 17q21 chromosome for an association with asthma. They accounted for participants’ environmental exposure to tobacco smoke early in life.

Results show three genetic variants on the chromosome were highly associated with early-onset asthma, or asthma striking children age 4 or under. Exposure to environmental tobacco smoke worsened the risk. These findings support the idea that early-onset and late-onset asthma are different conditions with different genetic foundations.

“Our study confirms the association between 17q21 markers and asthma and shows that these markers confer susceptibility specifically to early-onset asthma, thus supporting the hypothesis that asthma with an onset in early life may differ biologically from asthma with a later onset,” study authors wrote.

SOURCE: New England Journal of Medicine, 2008;359:1985-1994