Can't quit? It's in your genes

If you smoke and find it impossible to give up, it may not be your fault.
Some people have a gene which makes it especially hard to quit, a study suggested yesterday.

But the mutant gene also leads smokers to light up less frequently and appears to protect against emphysema, a serious smoking-related illness.

Known as CYP2A6del, it is a defective version of a gene which helps break down nicotine in the body.

Japanese scientists took DNA from 203 existing or ex-smokers with suspected chronic obstructive pulmonary disease and compared it with DNA from 123 healthy volunteers.

COPD, a combination of emphysema and chronic bronchitis, causes airflow in and out of the lungs to be disrupted.

The findings, published in the medical journal Thorax, showed people with the rogue version of the gene were much more likely to find it impossible to give up cigarettes.

Apossible explanation is that the mutant gene makes it harder to break down nicotine, allowing its addictive effects to last longer. Dr Hidetoshi Nakamura, of Keio University in Tokyo, said: 'The prolonged presence of nicotine in the circulation may inhibit subjects with this defective gene from withdrawing their dependence on nicotine when they try to quit.'

This is why people with the gene mutation tend to be lighter smokers - they would not need to have many cigarettes to get a nicotine high.

The absence of certain substances normally obtained from the breakdown of nicotine was the reason the gene variant seemed to protect against emphysema, the researchers added.