The study findings, which appear in the September issue of Alcoholism: Clinical and Experimental Research, also suggest that the protective effects of this gene may be undermined by a culture that encourages drinking.
The gene, ADH2*2 is a rare variation of ADH2, which produces a more active form of alcohol dehydrogenase, the enzyme that catalyzes the first step in alcohol metabolism. However, explains lead author Deborah Hasin, Ph.D., from Columbia University and the New York State Psychiatric Institute, "the exact reason why ADH2*2 tends to discourage heavier drinking isn't known."
"Recently, reports have shown a relatively high prevalence [approximately 20 percent] of ADH2*2 in Jewish samples ... suggesting that ADH2*2 is one of the factors explaining the low rates of alcoholism in this group," Hasin notes. Earlier research has shown that differences in religious practice and level of religiosity cannot account for these low rates.
Indeed, recent investigations have demonstrated "significant relationships between ADH2*2 and alcohol use ... in all Jewish groups studied," Hasin reports. Those with the variant gene have been seen to drink less frequently, consume less alcohol overall or have more unpleasant reactions to alcohol. Until the present study, however, the relationship between ADH2*2 and level of dependence on alcohol was not explored.
Hasin and her colleagues recruited 75 Israeli Jews aged 22-65. Trained interviewers employed a widely used questionnaire to assess each participant's current, past and lifetime level of alcohol dependence. Sixty-eight of the participants provided genetic material to test for the presence of ADH2*2.
The results revealed that participants with ADH2*2 had significantly lower indicators of alcohol dependence over their lifetimes.
"This finding adds to the growing body of evidence that this genetic variation has a protective effect against alcoholism among Jewish groups," Hasin concludes.
When the researchers divided the participants into three groups based on country of origin and recency of immigration, however, they found indications that the protective effect of ADH2*2 was not equally strong in every group.
The protective effect of ADH2*2 on alcohol dependence severity appeared stronger among the two more established groups of Israeli Jews, the Ashkenazis (those of European background and arrivals from Russia before 1989) and the Sephardics (those of Middle Eastern and North African background), than among more recent immigrants from the former Soviet Union.
Among those with ADH2*2, the recent Russian immigrants tended to have a history of much heavier drinking than their Sephardic and Ashkenazic counterparts. Levels of past and lifetime alcohol dependency -- but not current dependency -- were also highest among the recent Russian immigrants.
According to Hasin, one logical explanation for these findings is the fact that both genes and environment influence the development of alcohol dependence. "Russia has one of the world's highest levels of alcohol consumption," she notes, "whereas Israel has one of the lowest."
Hasin concludes, "The study's findings suggest that the recent Russian immigrants' previous exposure to the heavy-drinking environment of Russian culture overcame the protective effects of the ADH2*2 gene." Their increased vulnerability to heavy drinking was evidenced by such study measures as peak lifetime alcohol consumption levels.
The decrease in the recent arrivals' alcohol intake and dependency levels after immigration may reflect "acculturation to Israeli drinking patterns," Hasin proposes. "However," she adds, "other explanations, including a tendency to drink less as we age, cannot be ruled out."
The study was funded in part by the National Institute on Alcohol Abuse and Alcoholism.
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By Donna Abrahams