Each of the 23 genes somehow normally acts to reduce longevity, whereas inhibiting any one of them increases lifespan. For example, the worm's lifespan doubles when one gene is prohibited from working properly, and inhibition of another gene increases the length of life by 20%.

The genes discovered affect a wide variety of activities, including insulin signaling, metabolism, and dietary regulation. Genes involved in insulin signaling are particularly interesting because corresponding human genes could potentially play a role in diabetes and cancer, according to senior author Cynthia Kenyon, of the University of California, San Francisco, and her coauthors.

plosgenetics/

Genes can influence alcohol dependence, but they are not entirely responsible, according to Dr. Schuckit. "The same things that can be said about alcohol dependence can also be said about many medical and psychiatric conditions," he commented. "Let's use heart attacks as an example. They run in families, they appear to be genetically influenced, but it's unlikely there is a heart attack gene. What is likely is that in some families what is being passed down is another condition, such as high blood pressure or high blood fats, which then increases the risk for heart attack. For many genetically influenced disorders or conditions, people are more likely to inherit a gene for an intermediate characteristic than a gene for the condition itself. The characteristic, such as the intensity of response to alcohol, then interacts with environment to increase or decrease risk."

There also are genetic characteristics other than the level of response to alcohol that may affect the risk of alcohol dependence. For example, a series of genes that impact alcohol metabolism can cause a more intense response to this drug and a subsequent lower alcoholism risk.

Also, some families pass along a characteristic called impulsivity, which is influenced by genes as well as environment. "If a family carries a high risk of impulsivity and it is passed on to a child, that child is at high risk for alcoholism, drug dependence, gambling and violence," said Dr. Schuckit. He estimates that 20 percent of alcoholics carry their risk through the impulsivity characteristic.

Dr. Schuckit concluded, "The more we understand about the causes of alcohol dependence and the contributing genes, the more likely we will be able to identify tailored preventions and better evaluate treatments once alcoholism develops."

ama-assn/