Gene Variations, Secondhand Smoke Linked to Early Asthma

Oct. 16 -- WEDNESDAY, Oct. 15 (HealthDay News) -- Certain genetic variations previously identified as putting people at higher risk for asthma apparently only increase the risk of so-called early-onset asthma, which is disease that appears at 4 years of age or younger.

The risk is further increased by exposure to secondhand smoke, again early in life, according to a study in the Oct. 16 issue of the New England Journal of Medicine.

"This helps support the theory that asthma is not a uniform disease. It's probably several problems that end up with the same type of symptoms," said Dr. Thomas Leath, assistant professor of pediatrics at the Texas A&M Health Science Center College of Medicine. "It also 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."

Another striking point in the study was the clear cut-off point of 4 years of age, experts said.

"It seems clear that there are certain genetic loci that are connected with early onset asthma -- that wasn't surprising," said Dr. Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City. "What was interesting was the interlude between nature and nurture. 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. That illustrates that while something can be genetically determined, it can be amplified by environmental factors."

Even so, the study results won't have any immediate clinical implications, said Leath, adding, "It's a great step in the right direction, but we don't know what to do with it."

Asthma is increasingly recognized as a number of separate diseases, rather than one, overarching disease. Not much is known about the causes of different forms of the respiratory condition, and understanding the causes could help unravel the biological mechanisms behind the disease processes.

The age at which asthma begins is one way to differentiate different types -- or "phenotypes" -- of the disease.