Three research groups announced Wednesday that they have identified a widely distributed genetic variation that appears to increase the odds of developing lung cancer.
Although 80% of lung cancer cases are attributable to smoking, scientists have long known that genetics play a role. Family studies have shown that having a parent or sibling with lung cancer doubles or triples the odds of developing the disease.
Yet finding the genes that predispose people to lung cancer has been difficult.
The studies -- two in the journal Nature and one in Nature Genetics -- implicate a genetic variation located near a cluster of genes on chromosome 15 that are involved in the body's response to nicotine.
People who inherit the variation from one parent have a 30% greater chance of developing lung cancer, the published studies said. Those who inherit the variation from both parents face an increased risk of 70% to 80%.
The discovery may help to explain why some smokers don't develop lung cancer and why some occasional smokers don't become addicted, researchers said.
Smokers generally face a 15% chance of developing lung cancer; those with one copy of the genetic variation have about the same risk. Smokers who inherit two copies face about a 1 in 4 chance of developing lung cancer.
The groups detected the variation by analyzing the genomes of more than 35,000 smokers and former smokers, and a smaller number of nonsmokers, almost all of whom were from Europe, Canada and the United States.
About half of the people of European descent have one copy of the variation, scientists said, which is believed to be much less common in people of African or Asian descent.
The three studies were divided on whether the genetic variant directly increased the risk of lung cancer or did so indirectly by predisposing people to smoking.
One of the teams linked the variation to smoking addiction. Study author Kari Stefansson, chief executive of Iceland-based deCODE genetics, said smokers who had inherited one variant smoked an average of one more cigarette a day than other smokers. Smokers who had inherited two copies smoked an average of two extra cigarettes a day, he said.
People with the variant also had a more difficult time quitting, he said.
Stefansson said it was the extra cigarettes, and not the gene itself, that led to lung cancer. His group estimated that the variation was indirectly responsible for 18% of lung cancers and 10% of cases of peripheral artery disease, which is also linked to smoking.
