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SMOKERS who find it hard to cut down or quit may be at the mercy of their genes.

Scientists identified three genetic mutations that increase the number of cigarettes people smoke a day. Several also appear to be associated with taking up smoking, and one with being able to quit.

The findings could lead to more personalised — and ultimately more effective — treatments that help people stub out their cigarettes.

Three studies published online in Nature Genetics compared the DNA of about 140,000 people and discovered the desire to give up is down to your genes rather than willpower.

Two of them found regions associated with the number of cigarettes smoked per day. These include two genes that have been linked with nicotine dependence and two others that regulate nicotine metabolism in the body. Mutations in these genes are associated with a small increase in smoking quantity but around 10 per cent increase in risk of lung cancer compared with non- carriers.

Lead author Professor Kari Stefansson, a neurologist at deCODE genetics in Reykjavik, Iceland, said: “ Smoking is bad for anyone’s health. It is worse for some. To some degree these variants suggest those for whom nicotine is more addictive are driven to smoke more.

But it may also be they make people more susceptible to the effects of tobacco smoke. These variants — which are all near genes that encode nicotine metabolising enzymes and receptors — are giving us a solid starting point for finding answers to advance personal and public health.” A third study by Clyde Francks, of the University of Oxford, and colleagues found variants of three genes on chromosome 15 that make people more prone to nicotine addiction. “ Smoking behaviour and nicotine dependence are multifactorial traits with substantial genetic influences,” he said.