THURSDAY, July 17 (HealthDay News) -- People with certain common genetic variations that affect their nicotine receptors seem to be at higher risk for becoming life-long nicotine addicts if they begin smoking before they turn 17, a new study says.

"We know that people who begin smoking at a young age are more likely to face severe nicotine dependence later in life," Robert Weiss, study lead author and professor of human genetics at the University of Utah, said in a university news release. "This finding suggests that genetic influences expressed during adolescence contribute to the risk of lifetime addiction severity produced from the early onset of tobacco use."

The findings should one day help with public health interventions to counter smoking, the researchers said.

"In recent years, we've seen an explosion in the understanding of how small genetic variations can impact all aspects of health, including addiction," said Dr. Nora Volkow, director of the U.S. National Institute on Drug Abuse (NIDA), also in the news release. "As we learn more about how both genes and environment play a role in smoking, we will be able to better tailor both prevention and cessation programs to individuals."

The study was published in the July 11 issue of PLoS Genetics and, in addition to researchers at the University of Utah, involved investigators at the University of Wisconsin-Madison.

The gene variations in question are called single nucleotide polymorphisms (SNPs). SNPs that are linked and passed on together are called a haplotype.

In this study, which involved 2,827 long-term smokers of European-American descent, one haplotype for the nicotine receptor increased the risk of individuals becoming heavy smokers later in life.

Participants who took their first drag on a cigarette before the age of 17 and who also had two copies of the high-risk haplotype had a 1.6- to almost five-fold increased risk of being heavy smokers as adults.

Those who had the haplotype but did not begin smoking until 17 or later were not at an increased risk of life-long addiction.

People with a second haplotype had a reduced risk of becoming heavy smokers as adults even if they acquired the habit as youngsters, the study said.

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