The key to giving up smoking may lie in genes rather than willpower, a study shows. Some people have a defective gene that makes quitting more difficult, scientists found. But the same gene appears to protect against emphysema, a smoking-related illness.

The key to giving up smoking may lie in genes rather than willpower, a study shows. Some people have a defective gene that makes quitting more difficult, scientists found. But the same gene appears to protect against emphysema, a smoking-related illness.

People with the gene are also more likely to be light smokers, because fewer cigar-ettes are needed for them to get a nicotine "high".

Scientists in Japan took DNA from 203 present and former smokers with suspected chronic obstructive pulmonary disease (COPD) and compared it with DNA from 123 healthy volunteers. COPD is a combination of chronic bronchitis and emphysema, which causes persistent disruption of air flow in and out of the lungs.

The researchers, led by Dr Hidetoshi Nakamura from Keio University in Tokyo, noted the number of cigarettes participants smoked per day, and the length of time they had been smokers. Those who had stopped were asked how long it had been since they had a cigarette.

Scientists have already identified a gene that assists breakdown of nicotine in the body. But the Japanese scientists have identified a mutant version of the gene, called CYP2A6del, which makes it harder for this breakdown to occur, and therefore makes quitting more difficult.

The findings, in the journal Thorax, showed that people with the CYP2A6del version of the gene were significantly more likely to be present rather than former smokers.

The scientists wrote: "The prolonged presence of nicotine in the circulation may inhibit subjects with this defective allele (gene variant) from withdrawing their dependence on nicotine when they try to quit smoking.

"In future, the CYP2A6 genotype should be determined when nicotine replacement therapy is considered because the nicotine concentration in the blood is expected to differ in smokers with different genotypes."

For the same reason, the gene mutation would lead some people to be light smokers. They would not need to consume very many cigarettes to get a sufficient nicotine "high".

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