We now may have the beginnings of understanding why some people find it so difficult to stop smoking even when they are in treatment for this problem. According to statistics provided by the Centers for Disease Control and Prevention (CDC), tobacco use is the leading preventable cause of death in the United States, and it is the second major cause of death in the world according to the World Health Organization (WHO). An estimated 20.9% of all US adults smoke, and even with a strong desire to quit, most find it exceptionally difficult. A new study being published in the September 15th issue of Biological Psychiatry reports that genetic variation in a particular enzyme affects the success rates of treatment with bupropion, an anti-smoking drug.
Lee and colleagues performed CYP2B6 genotyping on smoking individuals, a gene that is known to be highly variable and whose enzyme metabolizes both bupropion and nicotine. Participants were then provided with either placebo or bupropion treatment for ten weeks. The authors discovered that individuals with the CYP2B6*6 allele of the gene benefited from bupropion treatment and maintained abstinence longer while doing poorly on placebo, with a 32.5% abstinent rate vs. 14.3%, respectively. In contrast, those in the CYP2B6*1 group did well on both bupropion and placebo, with similar abstinence rates at the end of treatment and after a six month follow-up.
Rachel Tyndale, M.Sc., Ph.D., one of the authors on this study, comments, This first study, while requiring replication, identifies a very common genetic variant that appears to affect smoking cessation treatment outcome. This variant is present in 25-50% of people, thus affecting a large portion of the population.
John H. Krystal, M.D., Editor of Biological Psychiatry and affiliated with both Yale University School of Medicine and the VA Connecticut Healthcare System, adds his thoughts about this exciting new data: We look forward to the era of personalized medicine, when doctors are able to use genetic information about their patients to guide treatment. We are not ready to use this information in clinical practice, but this study provides us with a good example of the type of information that might, some day, guide the treatment for smoking."
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What the researchers found is that fetal alcohol-exposed infants who carried a copy of the short form were more irritable and reactive to stress than either control group infants who weren't exposed to alcohol or those who were exposed but had two copies of the gene's long form. Overall, says Schneider, the results indicate a "substantial interaction" between fetal alcohol exposure and genotype.
She and her colleagues are now conducting additional studies to see if these findings fit a larger pattern of fetal alcohol-induced problems as the monkeys grow up. At the same time, extreme irritability and stress responsiveness in infants can themselves lead to problems, she says.
"If a baby is very irritable and stress reactive, one of the things this can interfere with is the caregiver-infant interaction," she says. "In real life, negative events tend to cluster. So if there's alcohol in the environment, there may also be stress. And then if you have an irritable baby, this all could have cascading effects on the child's psychological development."
Recognizing that complex behaviors are seldom, if ever, governed by a single gene, Schneider and her colleagues are also investigating other gene alleles for their potential to interact with fetal-alcohol exposure and put children at risk.
"Genetics by themselves rarely tell us much, because life experiences may trigger the actual effects of our genetic vulnerabilities," says Schneider. "So the more knowledge we have about the ways that genes interact with environmental factors, the more we can envision interventions early in life to help a vulnerable child."
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