Gene clue to nicotine addiction in teens

People who are slower to clear nicotine from their bodies are more likely to become addicted to cigarettes, a Canadian study shows. Scientists at McGill University, Montreal, looked at a group of teenagers who had recently started smoking. They found that those with a genetic variation that slows down the liver's ability to remove nicotine from the body smoked fewer cigarettes, but were more likely to become addicted.

The study, published in the journal Tobacco Control, looked at around 1,200 13-year-olds living in Quebec. At the start of the study, 228 of the participants smoked, but none were hooked on the habit. The scientists followed these teenagers for two years, after which time 67 became addicted to nicotine. They then looked at which version of a gene called CYP2A6 they had, which makes a protein responsible for breaking down toxins in the liver. The team found that participants with 'inactive' versions of the CYP2A6 gene were nearly three times more likely to become addicted as those with normal versions of the gene.

The researchers also identified a link between the CYP2A6 variations and the number of cigarettes smoked by the teenagers. Those with inactive genes, which slowed down the removal of nicotine the most, smoked around 12 cigarettes a week. Those with partially inactive genes smoked around 17, whereas as those with fully active CYP2A6 genes smoked an average of 29 cigarettes a week. The scientists think that the longer the nicotine remains in the body, the more the brain is exposed to its effects, increasing the chances of addiction. So although young smokers with the inactive genes are likely to smoke less, they are also more likely to get hooked than heavier smokers.

Variations in several different genes are thought to affect a person's risk of becoming addicted to nicotine, alcohol and other drugs. Earlier this month, US researchers identified a gene that affected the levels of nicotine required to trigger addiction in mice. Studies have also shown that genes can influence the effectiveness of nicotine patches in people trying to kick the habit. Commenting on the Canadian study, John Britton, from the British Thoracic Society, told BBC News Online: 'Our focus must be to prevent young from taking up smoking in the first place'.