Struggling to quit smoking? Now you can blame your genes

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 a total of more than 140,000 people and discovered the desire to give up is down to your genes rather than willpower.

Two of them found regions associated to the number of cigarettes smoked per day that 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 - about half a cigarette a day - 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 even worse for some.

'To some degree these variants suggest those for whom nicotine is more addictive are driven to smoke more, increasing their exposure to environmental risk.

'But given the quite substantial corresponding increases in risk of lung cancer it may also be that they make people more susceptible to the noxious effects of tobacco smoke.

'What is clear is that these variants - which are all near genes that encode nicotine metabolizing enzymes and receptors - are giving us a solid starting point for finding answers to advance personal and public health.'

A third study by Dr 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. Nicotine is the primary chemical responsible for smoking addiction.

He said: 'Smoking behavior and nicotine dependence are multifactorial traits with substantial genetic influences. There is an urgent need to better understand the molecular neurobiology of nicotine dependence in order to design targeted, more effective therapies.

'These findings have provided further new insights into the biology of smoking behaviour.'