Addicted to smoking and unable to quit? Your genes may be partly to blame, according to a trio of studies published Sunday in Nature Genetics that link several gene variants to a range of smoking habits, as well as increased risk for lung cancer.

Collectively, the researchers on the studies analyzed the DNA profiles of more than 140,000 people - smokers and nonsmokers. They also studied whether genetic variants affect whether people start smoking, how much they smoke and whether they are able to quit.

In one study, researchers found that a single-letter change in the DNA code of chromosome 11 was strongly associated with taking up smoking and another on chromosome 9 was associated with quitting smoking. (Humans have 23 pair of chromosomes).

“This lends support to the idea that smoking is not just a question of will power alone, but that genetics plays a role in how much a person smokes and their ability to quit smoking,” Dr. Helena Furberg from University of North Carolina, Chapel Hill, who was involved in the research, noted in an email to Reuters Health.

“We hope that our findings will help pave the way for better treatments that will help people quit smoking,” said Furberg. She emphasized, however, that more research needs to be done before the findings will benefit people directly. “At this time, getting tested for these variants will not tell you anything meaningful about your risk of smoking or ability to quit smoking,” the researcher noted.

In another study, a team of researchers led by scientists at deCODE Genetics in Reykjavik, Iceland, found that smokers who carry specific gene variants on chromosome 8 and 19 smoke more - about half a cigarette extra each day - and run a 10 percent higher risk of getting lung cancer compared to non-carriers.

The third study confirms and refines a discovery made two years ago by deCODE scientists and others of a gene variant on chromosome 15 associated with nicotine addiction and increased risk of lung cancer.

“These are fairly common variants,” deCODE chairman and senior investigator Kari Stefansson told Reuters Health.

NATURE VERSUS NURTURE

“There is debate about the relative importance of nature (genes) versus nurture (environment) in the development of common diseases,” Stefansson added. Studies have shown that while environment plays a key role in whether or not someone takes up smoking, genetics plays a role in whether or not they continue to smoke and how much.

“Our research shows that there is a genetic predisposition to become addicted to nicotine,” Stefansson said.

Smoking causes 9 out of 10 cases of lung cancer, but only a small proportion of smokers actually develop the disease, further evidence, researchers say, that a person’s genetic makeup is a factor.

“Smoking is bad for anyone’s health, Stefansson noted in a written statement. “It is even worse for some, and today’s discoveries continue to strengthen our ability to identify who those people are and give them a compelling reason to quit. We plan to incorporate these (variants) into our testing products to do that.”

SOURCE: http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.571.html http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.573.html http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.573.html

Nature Genetics, online April 25, 2010.