A study conducted by deCODE Genetics Inc found gene variants that could be linked to an increased affinity for smoking and the risk of lung cancer. The study included 14,000 smokers and found that nicotine receptor genes affect how much one smokes as well as their dependence on smoking.

“In addition, we found a gene variant which confers nicotine dependence also confers a fairly substantial risk of lung cancer and peripheral arterial disease,” says Katie Stefansson, MD, president of deCODE. “So people who have inherited this variant from one parent have a 30% greater risk of developing lung cancer.”

The variant is found in about 40% of the population.

A second study from the International Agency for Research on Cancer in Lyon, France, looked at 11,000 people—4,500 of them had lung cancer. Researchers found two variants that affect nicotine addiction and also make cells increase in number, which may increase the chances of developing a tumor.

“Variations in the region of chromosome 15 were more common in cases of lung cancer than controls, far above what we would have expected by chance,” says Paul Brennan, lead researcher.

Those with one variant had a 30% increase in risk for lung cancer and those with two variants had an 80% increase in risk. How much and how often one smoked did not affect the risk for lung cancer. In addition, the gene variants were found among people who never smoked.

A third study, included 3,000 patients with lung cancer who had been smokers. This study, conducted at the M.D. Anderson Cancer Center in Houston, also found the 30% and 80% increased risk for lung cancer.

“What is remarkable about our studies is how similar the results are with respect to lung cancer risk,” says Christopher Amos, MD.

None of the studies made it clear whether these gene variants represent a direct risk for lung cancer and increased susceptibility to smoking.

The first two studies were published in the April 3 edition of Nature, and the third was published in the April 2 edition of Nature Genetics.