Vulnerability To Compulsive Gambling Is Partly Inherited

Casinos, gambling boats and state lotteries have become popular ways to raise revenue and provide some excitement for those who donate their dollars. But as legalized gambling has become more common in the United States, gambling problems have too. In part, that's because some of us are genetically predisposed to certain gambling behaviors.

Researchers at Washington University School of Medicine and the Veterans Affairs Medical Center in St. Louis studied twins to get a better idea of genetic influences on gambling behavior. Reporting in the September 1998 issue of the journal Addiction, they say genes have a significant influence on at least two behaviors that contribute to compulsive gambling.

The researchers studied 3,359 pairs of male twins. All were part of a Department of Veterans Affairs database of twins who served in the military during the Vietnam War. The sample included both identical twins, who have exactly the same genes, and fraternal twins, who share about half of their genes.

"Because all of these twins were brought up in the same household, we can control for differences in formative experiences during youth. Those experiences will tend to be very similar, so with both identical and fraternal twins, we are able to zero in on inherited factors," explains Seth A. Eisen, M.D., principal investigator, associate professor of medicine at Washington University School of Medicine in St. Louis and staff physician for the Department of Veterans Affairs. "By comparing the sharing of a particular behavior in identical twin pairs with that in fraternal twin pairs, we can estimate the inherited and noninherited contributions to that behavior."

The study was funded by grants from the Department of Veterans Affairs Health Services Research and Development Service, the National Institutes of Health and the Public Health Service.

In the genes

To be officially diagnosed with a psychiatric condition called pathological gambling disorder, an individual must exhibit at least four of nine behaviors, which include gambling larger amounts than intended, irritability if unable to gamble and sacrificing important activities in order to gamble.

"We were able to estimate the specific genetic component for two of those gambling behaviors," says Eisen. "One was gambling larger amounts than intended, and the other was repeated efforts to reduce or stop gambling. For those two symptoms, we found that about half of the gambling behavior was genetically mediated."

For three other behaviors -- attempts to win back losses at the same place, frequent preoccupation with gambling and increased betting to maintain interest -- the researchers were able to identify a familial vulnerability. That is a combination of inherited factors and environmental experiences during growth and development.

The prevalence of each gambling behavior that was common enough to study, was higher in identical twins than in fraternal twins. So if one identical twin exhibited a particular behavior, the odds were high that his twin also would exhibit that behavior. The odds were lower in fraternal twin pairs, which are less similar genetically than identical twins. The researchers therefore concluded that genetic influences are an important explanation for vulnerability to many gambling behaviors.

A major influence

In this sample of twins, 1.4 percent met the official criteria for pathological gambling disorder, which is about the same as reported in other studies of middle-aged American males. Although the total number of compulsive gamblers was low, the genetic contribution to gambling behavior was very high. The researchers estimated that genetic factors influenced about 35 percent of the gambling behavior of study subjects who gambled at least 25 times a year but had no pathological symptoms.

Because such a small percentage of the sample were compulsive gamblers, Eisen and colleagues were unable to tease out all of the various influences and determine the exact genetic contributions for several gambling behaviors. But, they found that familial factors explained 62 percent of the behavior of those reporting four or more symptoms, the official definition of pathological gambling disorder.

"So we see that vulnerabilities to gambling behavior, even if not completely genetic, are certainly influenced by inherited factors and by early environmental influences," Eisen said.

Between one and three percent of the American population has major gambling problems, and many more people who don't meet the official criteria for pathological gambling have problems with gambling that adversely affect their lives and relationships.

That negative influence is becoming more apparent as gambling becomes more widely available. When placing a bet meant traveling to Las Vegas or dealing with a bookmaker, people with a genetic risk for compulsive gambling had fewer problems. Now, it's often a matter of heading to the nearest grocery store to buy a lottery ticket.

"It is becoming increasingly easy to gamble in the United States -- particularly in the last 10 years or so -- and problems with gambling are much more common now than they were previously," Eisen says. "Presumably that's because some of us are vulnerable to becoming gamblers because of our genes and/or experiences when we were very young. With our increased access to gambling, some of us develop problems."

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Note: For more information, refer to Eisen, SA., et al, "Familial Influences on Gambling Behavior: An Analysis of 3359 Twin Pairs," Addiction, vol. 93, number 9, pp. 1375-1384, Sept. 1998.