Smokers who have tried to give up cigarettes and failed may soon be able to come up with another excuse - they were born to remain addicted. In the first study of its kind, scientists have identified a series of genetic traits for addictiveness that appear to be inherited by smokers who try but fail to kick the habit.
Scientists believe that the findings could soon open the way to testing a person's genetic make-up to see whether they can be weaned off cigarettes with the help of specially-targeted treatments.
"The long-term hope is that identifying genetic variables in smokers will help us determine which type of treatment would be most effective," said Jed Rose, of Duke University in Durham, North Carolina.
"Knowing a smoker's genetic make-up could indicate how intensely they need to be treated. People who are having trouble quitting because of their genes might need more treatment to overcome their addiction," Dr Rose said. The latest research into the addictiveness of cigarettes suggests that genes play a significant role in making someone dependent on smoking in the first place, and making it more difficult for them to quit once they have started.
It is part of a wider study of the human genome to investigate the genes that appear to play an important role in the formation of a person's psychological make-up, such as an inherited predisposition to addictiveness or risk-taking behaviour.
"This research marks the first time we've been able to identify genes involved in the ability to quit smoking," said Dr Nora Volkow, the director of the US National Institute on Drug Abuse in Washington.
"It marks a movement from identifying the genetics of addiction vulnerability to identifying the genetic basis of successful abstinence. This knowledge could impact the success rate of cessation programmes by helping health care providers choose the most appropriate treatment based on individual differences."
The scientists, who were funded by the US government and Philip Morris, the cigarette makers, screened more than 520,000 genes to compare the genetic variations found among smokers who had successfully given up with genetic variations among smokers who had tried to quit but failed.
"We identified 221 genes that distinguished successful quitters from those who were unsuccessful," said Dr George Uhl, who carried out that analysis at the National Institute on Drug Abuse.
"We know the functions of about 187 of these genes, but 34 have functions that are unknown at present.
"We also found that at least 62 of the genes that we had previously identified as playing roles in dependence to other drugs also contribute to nicotine dependence," he said.
"These findings lend further support to the idea that nicotine dependence shares some common genetic vulnerabilities with addictions to other legal and illegal substances."
One of the genes that appears to differ between smokers who give up and those who cannot is called cadherin 13, which produces a substance known to be involved in controlling how nerve cells in the brain stick together, Dr Rose said. "Smokers whose nerve cell connections are not working properly may be more vulnerable to addiction and may face a tougher time quitting. These findings open up new possibilities in finding specific targets for treatment."
Another of the genes involved in smoking addictiveness is also known to play a role in controlling how people respond to stress - the gene produces a protein that is important in guiding learning processes in the brain, Dr Uhl said.
The next stage of the research will involve testing different forms of treatment for giving up smoking to see how effective they are on people with differing genetic make-up, Dr Volkow said.
"We soon may be able to make use of this information to match treatments with the smokers most likely to benefit from them," Dr Volkow said.
The research is published in the journal, BioMed Central Genetics.
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