Israeli Discovery Explains Why Smoking Slows Down Development of Parkinson's

Initial findings show a link between nicotine dependence and a protective mechanism against Parkinson's disease, but only in people who had been exposed to nicotine in the past.

Israeli scientists have identified the genetic mechanism that protects cigarette smokers from Parkinson's disease, which could ultimately lead scientists closer to a treatment for the degenerative disorder.

The relationship between Parkinson's and smoking has been known since 2001, when an article in the medical journal Epidemiology first reported that cigarette smokers were 60 percent less likely to develop the disease, and that the protective effect continued for 25 years after the person stopped smoking.

This month, a research team announced the results of genetic tests conducted on blood samples from 677 Italian Parkinson's patients, 438 of whom never smoked cigarettes and 239 of whom currently or used to smoke. Initial findings show a link between nicotine dependence and a protective mechanism against Parkinson's disease, but only in people who had been exposed to nicotine in the past.

Among the genes researchers studied were those that were part of a gene cluster known as CHRNB5, CHRNB4 and CHRNB3. According to the study, it appears that as these genes became more dependent on nicotine, they also became more responsible for holding back the progress of Parkinson's.

No significant impact was found on the development of the disease among Parkinson's patients who did not smoke.

The research is being carried out jointly by the Hadassah University Hospital, the Hebrew University of Jerusalem, Beilinson Hospital, Tel Aviv University and research institutes in Milan, Italy. The research team is headed by Dr. Lior Greenbaum of the Hebrew University and Prof. Benjamin Lerer, director of the Psychiatric Biology Laboratory at Hadassah University Hospital in Ein Karem.

The new discovery also contributes to an understanding of how a mechanism in nicotine is utilized that protects against damage to the brain chemical dopamine. The disruption of the action of dopamine is connected to the development of Parkinson's.

The research is supported by a foundation established in 2000 by the actor Michael J. Fox, who suffers from Parkinson's disease. The findings were reported this month in the journal Parkinsonism and Related Disorders. Researchers note that more studies must be conducted on a wider population in order to determine the validity of the results.

"It cannot be assumed from the findings that smoking cigarettes is good for health. On the contrary, there is no doubt that the risk in smoking is much greater than the benefit," Dr. Lerer said. "The combination of genes that has been identified is important because it allows us to better understand the mechanism by which smoking reduces the likelihood of Parkinson's. The discovery makes it theoretically possible to develop a treatment for Parkinson's directed at the genes that have been found."

In recent years, Lerer and his team have studied the genetic mechanisms that influence nicotine dependence. The current discovery could serve as a theoretical contribution to the development of future genetic treatments to help people stop smoking.

The protective effect of cigarette smoking against Parkinson's, which strikes one in 20,000 Israelis, is one of the only proven medical benefits of smoking. In 2002, researchers from Yale University found that smoking had a positive effect on the visual memory of schizophrenics because, Lerer explained, nicotine might have the effect of correcting some physiological disorder characteristic of schizophrenia, apparently in the filtering of external stimuli.