Scientists Find Genetic Link to Smoking Addiction

Three scientific research teams announced last Wednesday, April 2, that they had identified genetic variations that raise the risk of lung cancer and tobacco addiction in smokers and former smokers. Researchers are calling it a major step forward in the fight to find out why certain people are susceptible to non-small cell lung cancer, which is responsible for up to 80 percent of all lung cancer cases.

Three separate research teams, writing in the journal Nature and Nature Genetics, each pinpointed two key areas of variation on chromosome 15. These variants are quite common in the general population but they only raise lung cancer risk in those who have smoked. Current or former smokers who are carrying two copies of both variants-one inherited from each parent-have a raised risk of 70 to 80 percent. Individuals who carry both variants represent about 15 percent of smokers. Smokers who carry only one copy of each variant also have a raised risk of developing lung cancer, but this increase is only around 28 percent.

The research teams disagree on how the key variants specifically influence lung cancer risk. A team from the Icelandic company deCODE Genetics, which was in charge of the largest study, stated that their findings suggest that carrying the variants makes people more addicted to tobacco once they start smoking. However, an international team that included scientists from the Institute of Cancer Research, the University of Cambridge, and Johns Hopkins University believes it is more likely that the variants interact directly with tobacco to cause lung cancer-possibly by increasing the likelihood that nicotine will trigger the uncontrolled cell division that characterizes cancer.

Each of the research groups studied the DNA of thousands of current and former smokers, all of whom were of European descent. Despite the large number of sample subjects, all three of the teams found that a particular pattern of gene variation at two points of chromosome 15 was noticeably more common among people who developed lung cancer than among those who were healthy. The teams also stated that it remains to be seen whether the key set of variations affect just one gene, or three closely connected genes.

Data collected by the U.S. Centers for Disease Control and Prevention (CDC) has revealed that lung cancer kills more people than any other cancer-in fact, more than breast cancer, colon cancer, and prostate cancer combined. The American Cancer Society predicts that in 2008 there will be about 215,020 new cases of lung cancer, with 161,840 of them resulting in death. According to statistics obtained bythe BBC, half of all smokers will eventually die from lung cancer or another smoking-related illness.

Dr. Lesley Walker of the Cancer Research UK charity told the BBC, "We know that smoking greatly increases the risk of lung cancer . . . [but] this research tells us there are some smokers who are even more vulnerable to lung cancer because of their genetic profile."