For many common diseases, environment is far more important than genetics in determining whether a person will be affected. One of the best examples of this is lung cancer. Nearly 90% of the cases of this disease can be attributed to smoking.
Today at the American Association for the Advancement of Science meeting in Chicago, however, Thorgeir Thorgeirsson of deCODE Genetics suggested that genetics may help foster a better understanding of the environmental risk factors for lung cancer.
Several studies published in April 2008, including one authored by Thorgeirsson, showed that a variation on chromosome 15 is associated with increased odds of lung cancer. Thorgeirsson’s group also showed that this same variation is associated with increased smoking — about one cigarette per day per copy of the riskier version (Read more here.)
Together these findings raise an important question: does this variation increase the odds of cancer because it increases the amount a person smokes?
According to Thorgeirsson, there should be only a 5% increase in the odds of developing lung cancer based on the increase in smoking associated with the genetic variation. But the data indicate that each copy of the riskier version actually increases odds of the disease by about 30%.
This, Thorgeirsson suggested, could mean that the variation is associated not just with smoking quantity, but also with another behavior, such as how deeply a smoker inhales or how far down he usually smokes his cigarettes. He noted a recent study published in Cancer Research that found that, compared to smokers without the genetic variation, those with it take in more nicotine and carcinogens with every cigarette.
Another possibility is that the variation has a dual effect. It could increase not just smoking quantity, but also the vulnerability of a person’s cells to the harmful effects of the smoke.
Although there’s still much work to be done in order to fully understand the effects of this particular genetic variation, the results so far hint at the fact that genes and environment may for more interconnected than previously appreciated.