The Role of Genes in Alcohol Dependence
Jul 22, 2005 - 12:31:38 AM
Clues looking into the root causes of alcoholism are emerging from new findings that center on the genetic patterns of young drinkers, with particular focus on why adolescents are more likely to drink large quantities of alcohol even if they need more alcohol to get the effects they desire.
"The study offers a unique perspective on the beginnings of the alcohol experience and usage patterns of 12-year-olds," explained principal investigator Marc Schuckit, M.D., professor of psychiatry at the Veterans Affairs San Diego Healthcare System. "This is the first study correlating the intensity of reaction to alcohol with the amount of alcohol consumed at an early age."
Dr. Schuckit, who also is distinguished professor of psychiatry at the University of California, San Diego Medical School, spoke today at the American Medical Association media briefing, Alcohol Dependence: From Science to Solutions, held in New York City. He also released his study "Performance of a self-reported measure of the level of response to alcohol in 12- to 13-year-olds" published in the July issue of The Journal of Studies on Alcohol.
In the study, 80 children in Bristol, England, who had some experience with alcohol responded to a questionnaire regarding their drinking habits. On average, the respondents reported drinking alcohol about five times in the previous six months. While most of them only consumed one or two drinks at a time, a significant number reported having four to six drinks at a time.
A low response to alcohol is a risk factor for alcohol dependence and a predictor of future alcoholism. "When children with a family history of alcohol dependence begin drinking, about half of them experience little or no intoxication at blood alcohol levels where others would be feeling moderately tipsy," said Dr. Schuckit. "Consequently, these adolescents have a propensity to drink more heavily when they drink because higher blood alcohol levels are required to produce the effects they want."
For the last 20 years, Dr. Schuckit has been researching the importance of a person's intensity of response to alcohol as one of several inheritable traits that may increase the propensity for alcohol dependence. His research team is searching for genes that may be related to this low alcohol response.
Three primary findings support the importance of genetics and alcoholism. First, the risk for alcohol dependence in the sons and daughters of alcoholics is four times higher than in the general population. Second, the rate of increased risk for alcoholism persists in children of alcoholics even if they are adopted at birth and raised by non-alcoholics. Finally, identical twins have a much higher rate of both becoming dependent on alcohol if one is--compared to the same rate for fraternal twins.
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."
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