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Montreal — A simple variation in one gene may increase a teen's likelihood of nicotine dependence, according to new research funded by the Canadian Cancer Society. This research — the first of its kind — is published online in today's issue of Tobacco Control.

"This is compelling new evidence for the influence of genetics on nicotine dependence," says Canadian Cancer Society researcher Dr Jennifer O'Loughlin. "We've found that teens with a certain genetic variation are at a higher risk of becoming nicotine dependent at very low levels of cigarette consumption — even just two to three cigarettes per day."

In her research involving Montreal teens, Dr O'Loughlin found a link between nicotine dependence and a variation in a single gene — called CYP2A6 — that controls how quickly we metabolize nicotine. A certain genetic variation of CYP2A6 slows down nicotine metabolism, likely resulting in prolonged brain exposure to the drug.

In her study, teens with the genetic variation were more likely to become nicotine dependent and they also smoked fewer cigarettes per week than teens with the normal CYP2A6 gene. The study's authors suggest that slower nicotine metabolizers sustain higher blood levels of nicotine over a longer period and therefore need to smoke fewer cigarettes.

"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," says Dr O'Loughlin, a professor in ºÚÁϲ»´òìÈ University's Department of Epidemiology, Biostatistics and Occupational Health. "This shows us why even a brief exposure to tobacco during adolescence can result in long-term addiction for some kids."

Dr O'Loughlin has been following a group of 1,200 Montreal teenagers since 1999 as part of a six-year study to investigate the genetic and environmental risk factors for nicotine dependence in youth.

For this arm of her study, the DNA from blood samples from 281 of the students was analyzed for CYP2A6. All of the students who provided a blood sample had previously smoked cigarettes or were current smokers. Students in her study also completed quarterly questionnaires that measured their smoking patterns and nicotine dependence, including withdrawal symptoms and cravings. Nineteen per cent of the students tested had an altered version of CYP2A6. Among students with the slowest nicotine metabolism, the risk of becoming tobacco dependent was three times higher than among normal metabolizers.

Last year, Dr O'Loughlin published findings from this research project showing that teens in her study who smoked only once or twice were already reporting common symptoms of nicotine dependence.

"This new research complements what we already know about the social and psychological reasons young people smoke," says Cheryl Moyer, Director of Cancer Control Programs, Canadian Cancer Society. "It highlights why prevention of experimentation of tobacco use is so important to our tobacco control efforts. It also opens doors for more effective smoking cessation programs that are tailored to each person's individual needs and cravings."

Tobacco use is the number one cause of preventable disease, disability and death in Canada. It is responsible for more than 47,500 deaths per year in Canada. Cigarette smoking causes about 30 per cent of cancers in Canada and more than 85 per cent of lung cancers.

According to the latest results from the Canadian Tobacco Use Monitoring Survey, 12 per cent of youth aged 15 to 19 years report themselves as daily smokers and seven per cent report occasional smoking. Slightly more teen girls smoke than boys (20 per cent versus 17 per cent); however, among daily smokers, boys smoke slightly more cigarettes per day (13) than girls (11.7).

The Canadian Cancer Society is a national community-based organization of volunteers whose mission is to eradicate cancer and to enhance the quality of life of people living with cancer. When you want to know more about cancer, or call the toll-free, bilingual Cancer Information Service at 1 888 939-3333.