By Amy Norton

NEW YORK (Reuters Health) - Evolution may have given certain East Asian populations a genetic defense against alcoholism, new research suggests.

Scientists have long known that many Asian people carry a particular variant in a gene called ADH1B, which causes people to become flushed, uncomfortable or even nauseated after drinking a small amount of alcohol -- making it unlikely that they'll become alcoholics.

In the new study, however, Yale University researchers found that only certain groups in East Asia have a very high prevalence of the protective gene variant, while it is less common in others. The findings suggest that some environmental factor in the relatively recent past made the gene variant advantageous for certain Asian populations.

The findings are published in the online journal PLoS One.

The ADH1B gene is one of a set of related genes that govern certain enzymes that metabolize alcohol. A variant of the gene called ADH1B*47His causes the body to convert ethanol (alcohol) to the hangover-producing chemical acetaldehyde more rapidly than normal.

This, in turn, appears to protect against alcoholism by making people ill from even a modest indulgence. The gene variant is highly prevalent in East Asia, fairly common in West Asia and North Africa, and rare elsewhere in the world.

In the current investigation, researchers led by Dr. Kenneth Kidd, a professor of genetics at Yale, studied the prevalence of the protective gene variant among different East Asian linguistic groups.

They found that the gene was most common in two of these groups -- those with Hmong and Altaic languages, which are scattered widely across Asia.

The fact that the gene variant was prevalent in these particular groups suggests that, at some point in the past few thousand years, something in the groups' environment caused the gene to become advantageous -- allowing carriers to survive at higher rates than non-carriers.

It's not known what that "something" was. However, it's not likely to be the anti-alcoholism effect, Kidd told Reuters Health, since that would not have offered an important survival advantage. In fact, he noted, it is only in fairly recent times that people have been consuming highly concentrated forms of alcohol.

One theory, Kidd explained, is that the gene variant protected certain Asian groups against a toxin that was present in their traditional foods, but not present in the diets of other Asian groups.

If that protected them from getting sick, or allowed them to be better nourished, then that could be a survival advantage, Kidd said.

Another theory is that the gene variant offered protection against parasitic infection, as high levels of acetaldehyde in the blood may have proved fatal to certain parasites.

Historically, alcoholism rates have been quite low in certain Asian populations, particularly in China. This research, Kidd said, aids in understanding why that is.

Even so, along with the genetics, there is probably also a cultural component to the low alcoholism rates. Kidd noted that if it is common for people in a particular culture to get sick from alcohol, then alcohol will probably not turn up in many social situations.

SOURCE: PLoS One, online April 1, 2008.

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