Vol. 11, No. 1, 2005 Page 5
New evidence that genes can affect a person's vulnerability to addiction comes from a study of teenagers' smoking habits.
Jennifer O'Loughlin and colleagues collected DNA samples from 228 7th-grade students who previously or currently smoked. The students completed quarterly questionnaires that assessed their smoking patterns, as well as the cravings and withdrawal symptoms they experienced if they attempted to quit.
The researchers then determined whether different variants of a gene called CYP2A6, which determines how quickly nicotine is metabolized, affected the students' vulnerability to developing a dependence on nicotine. Some variants of this gene are inactive or exhibit reduced activity, resulting in slowed nicotine clearance and thus prolonging the brain's exposure to the substance and possibly resulting in a more intense response.
O'Loughlin and colleagues detected no difference between students with the fully-active and partially-active variants of the gene. However, they found that students with the completely inactive variants of CYP2A6 were three times as likely as other students to become dependent on cigarettes.
Interestingly, while their risk of becoming addicted was greater, students with the inactive gene variants smoked fewer cigarettes (approximately 13 per week) than either students with low-activity variants (17 per week) or those with high-activity variants (29 per week). This suggests, the researchers say, that the inactive gene variant boosts the effects of nicotine, making it more addictive but also creating longer-lasting effects in users.
O'Loughlin says, "We know that early signs of nicotine dependence are a key factor in young smokers maintaining their new habit and eventually becoming addicted to tobacco. This shows us why even a brief exposure to tobacco during adolescence can result in long-term addiction for some kids."
The findings of the study are in line with a large body of evidence indicating that genes significantly influence the use of, and dependence on, potentially addictive substances including cigarettes, drugs, and alcohol. (see related article, Crime Times, 2005, Vol. 11, No. 1, Page 3.)
"Genetically decreased CYPA26 and the risk of tobacco dependence: a prospective study of novice smokers," J. O'Loughlin, G. Paradis, W. Kim, J. Difranza, G. Meshefedjian, E. McMillan-Davey, S. Wong, J. Hanley, and R. F. Tyndale, Tobacco Control, Vol. 13, No. 4, December 2004, 422-28. Address: Jennifer O'Loughlin, Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, 1020 Pine Avenue West, Montreal, Quebec, Canada H3A 1A3.
"Tobacco addiction a matter of genes for some teens, new Canadian Cancer Society research finds," news release, November 24, 2004.