Smoking Genes Identified

April 26, 2010 -- Common gene variants affect how much a person smokes, whether one becomes a smoker, how hard it is to quit, and risk of lung cancer from smoking, new studies find.

The studies, based on genetic information collected by an international consortium from more than 140,000 people of European descent, expand on a 2008 report linking a specific region of the genome to smoking behavior.

Overall, the effects of the genetic variations are small:

• A single variation in the part of the genome previously linked to smoking behavior affects how much a person smokes. It increases smoking by one cigarette a day for each gene carrying the variant DNA.
• Two newly found gene variants increase smoking by about half a cigarette a day for each gene carrying the variant.

Although the effects on smoking quantity may be small, gene variants appear to play a very large role in whether a smoker gets lung cancer.

In their 2008 study, Thorgeir E. Thorgeirsson of Iceland's deCODE Genetics and colleagues calculated that gene variants increase a smoker's risk of lung cancer by 30%.

Now the Thorgeirsson team, in collaboration with University of North Carolina researcher Helena Furberg, PhD, and colleagues, calculate that the newly found gene variants increase a smoker's odds of getting lung cancer by 10%.

And these aren't the only genetic effects:

• A variation in a different part of the genome appears to make it 6% more likely that a person will take up smoking.
• Another gene variant gives a smoker a 12% better chance of quitting smoking than a smoker who doesn't carry the variation.

Although the findings are interesting, they don't give smokers any reason to seek genetic testing.

"At this time, testing for these variants will not tell you anything meaningful about your risk of smoking or nicotine dependence," Furberg says in a news release.

That may change in the future.

"Smoking is bad for anyone's health. It is even worse for some," deCODE executive chairman Kari Steffansson says in a news release. "Today's discoveries continue to strengthen our ability to identify who those people are and give them a compelling additional reason to quit."

The Furberg and Thorgeirsson studies -- together with a third study by University of Oxford researcher Jason Z. Liu and colleagues -- appear in the April 25 online edition of Nature Genetics.