KEY POINTS:
A genetic variation that significantly increases the risk of tobacco addiction in 10 per cent of the population also dramatically lifts their chance of developing lung cancer, a study shows.
The large international study, including nearly 1000 people from Otago and Southland, has been published in the prestigious scientific journal Nature.
One copy of the gene variant, coded RS1051730, is present in half the population, and 10 per cent have two copies, said one of the researchers, Dr Greg Jones, of Otago University, at Dunedin.
Chemical receptors, on cells in the brain and blood vessels, that were activated by nicotine appeared to be more active in people with this genetic variation, Dr Jones said yesterday. This made them more likely to become addicted to smoking, if they took it up.
"Inheriting this one factor means they face a double whammy. Not only are they more likely to be heavier smokers, but their risk of lung cancer increases by 18 per cent and their risk of arterial disease goes up by 10 per cent." The increases - of addiction and disease risks - were greater in those with two copies than with one.
The genetic variation was far more common among heavy smokers, Dr Jones said, but it did not seem to predispose people to taking up smoking.
The increased lung cancer and arterial disease risks associated with having the genetic variant seemed to be independent of the effect of smoking more tobacco.
"The fact of smoking more - with this genetic marker - makes you more at risk. Even if you take that into account, there seems to be an increased risk from having the marker," said Dr Jones, of the university's Otago Vascular Research Group.
He said the significance of the study was that it showed how a genetic variation could alter an individual's environment - by increasing the risk that he or she smoked more tobacco.
Genetics researcher Associate Professor Martin Kennedy, of Otago University at Christchurch, said last night the study and two associated papers were the first to show that one main genetic variation had a major influence on smoking behaviour.
"I think they are pretty earth-shattering ... It looks like this gene has a big effect, but it won't be the whole story [on genes involved in nicotine addiction]."
The United States National Institute on Drug Abuse, which supported the study, said: "These results suggest for the first time that a single genetic variant not only can predispose to nicotine addiction but may also increase sensitivity to extremely serious smoking-related diseases."
"It also tells us there may be some people quite resistant to [existing quit-smoking] approaches," Dr Jones said. "By identifying those people we may be able to come up with new strategies ... based on their genetic profile."
ADDICTION GENES
* Nicotine addiction is related to a number of genes, and to factors in the environment.
* 10 per cent of the population have two copies of the genetic variation RS1051730.
* These people have a heightened risk of nicotine addiction.
* They also have an 18 per cent increased risk of developing lung cancer, and 10 per cent increased risk of arterial disease.
