US scientists suggest that whether smokers find it easy or hard to abstain from cigarettes could be down to their genetic make up. The study is published online in the journal BMC Genetics. The researchers were George Uhl, a neurologist and neuroscientist in the molecular neurobiology branch of the US National Institute on Drug Abuse (NIDA) and a team led by Jed Rose, director of the Center for Nicotine and Smoking-Cessation Research at Duke University Medical Center, North Carolina. Uhl, Rose and colleagues looked at the genetic differences between people who had successfully quit and stayed off cigarettes and those who failed to stay abstinent. They performed a genome-wide analysis on 520,000 genes from blood samples and found 221 genes that were different in the successful quitters compared to the unsuccessful ones. "We know the functions of about 187 of these genes, but 34 have functions that are unknown at present," said George Uhl. And at least 62 of the genes they had discovered before as being involved in drug dependence also played a role in nicotine dependence, he said. Two genes that were identified as examples whose variants influence quitting success and dependence vulnerability were cadherin 13, known to affect how cells connect to each other and is involved in cell adhesion, and a cyclic G-dependent protein kinase known to affect brain development. All the genes they found either play a role in intracellular signaling and intercellular interactions, or are involved in other processes which made sense. This is the first study to identify the genes involved in successful abstinence as opposed to addiction vulnerability said the NIDA. "The long-term hope is that identifying these genetic variables in smokers will help us determine which type of treatment would be most effective," said Jed Rose. Uhl says he and his team have replicated their findings in another sample, which was reported at the February 2007 meeting of the Society for Research on Nicotine and Tobacco. However, it is still not clear how the genes work to increase or decrease the ability to stay off cigarettes. To discover that, more research is needed. "These findings provide ample justification for continuing the search for even more genetic variants associated with smoking cessation success," said Dr Nora D Volkow, director of the NIDA. "We soon may be able to make use of this information to match treatments with the smokers most likely to benefit from them," she added.

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