The case-control study of lung cancer patients and healthy control subjects suggests that genetic variants of a receptor for a common brain chemical known as dopamine influence the probability of smoking addiction. Dr. Margaret Spitz, chairman of the department of epidemiology at M. D. Anderson, is lead author of the study that enhances the understanding of the biological basis for nicotine addiction. Even after years of smoking, some individuals are able to quit the habit while others are unsuccessful despite their cessation efforts. This study sheds light on why that may occur. The study is published in the March 4 issue of the Journal of the National Cancer Institute.
Dopamine is a neurotransmitter, a chemical that helps to pass messages between nerve cells.
Prior research has found that nicotine, alcohol, cocaine and other drugs that induce feelings of pleasure appear to act through the release of dopamine in certain parts of the brain that are thought to be the site of nicotine's reinforcing effect on smoking behavior. Dr. Spitz and her collaborators suggest that inherited variations in one of several distinct types of dopamine receptors, encoded by a gene on human chromosome 11, may be responsible for differences in individuals' response to nicotine. Among the lung cancer patients, 30.3 percent of the ever smokers carried the B1 variant, in contrast with the 13.3 percent of the never smokers, a difference that was not statistically significant. Among the control subjects, however, 30.9 percent of the ever smokers carried the B1 variant, versus none of the never smokers, a difference that was statistically significant according to Dr. Spitz. The researchers also report that individuals who carry the A1 variant began smoking at a statistically significant younger age than those who carry only the A2 allele and attempted to quit fewer times.