French researchers say a combination of genetic predisposition and exposure to secondhand cigarette smoke nearly triples the risk for early-onset asthma, HealthDay News reported Oct. 16.

Experts increasingly believe that asthma is actually a number of separate diseases rather than a single, overarching illness, and the results of the latest research "supports the fact that it's not just genes that cause asthma, and it's not just the environment, but the interaction between the two," said Thomas Leath, assistant professor of pediatrics at the Texas A&M Health Science Center College of Medicine.

The study showed a strong association between six genetic variants and early-onset (appearing at age 4 or younger) asthma in people exposed to secondhand smoke at an early age, with an almost threefold increase in risk among children with both the genetic variant and early exposure to smoke.

"It's clear that those kids exposed to secondhand smoke had much more of a flowering of the disease process than those who weren't," said Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City, adding that genetic predisposition to the condition "can be amplified by environmental factors."

The study appeared in the Oct. 16, 2008 issue of the New England Journal of Medicine.