A University of Michigan study suggests that a variant in a nicotine receptor gene may help explain why certain individuals who try a first cigarette move on to becoming regular smokers, HealthDay News reported Aug. 8. 

The study builds on previous research connecting variations of a known genetic region for nicotine to smokers' extent of use and level of dependence. In this study, researchers found that regular smokers were much more likely than experimenters who had not become regular smokers to have a less common form of the CHRNA5 gene.

"It appears that for people who have a certain genetic makeup, the initial physical reaction to smoking can play a significant role in determining what happens next," said senior author Ovide Pomerleau, founder of the university's Nicotine Research Laboratory.

The study involved a sample of 435 individuals in one of two groups: those who had tried at least one but no more than 100 cigarettes in their lifetime and those who had smoked at least five cigarettes a day for the past five years. The researchers explained that the gene variant they studied explains only part of smoking behavior, and that a more detailed analysis of how genetic and environmental factors interact is needed to understand why many people become regular smokers.

Canadian researchers recently identified the dopamine receptor subtype that controls the brain's initial sensitivity to the rewarding aspects of nicotine, helping to explain why some individuals appear to become addicted shortly after their initial exposure to tobacco.

Results of the University of Michigan study were published online Aug. 8 in the journal Addiction.