They have found that alcoholics who carry a certain form of a particular enzyme are more likely than other alcoholics who don't have the form to develop heart failure, even when both groups have drunk the same amount of alcohol over a lifetime.
"It's the first real demonstration of genetic vulnerability to alcohol-induced tissue damage in the heart," says Emanuel Rubin, M.D., professor and chair of pathology, anatomy and cell biology at Jefferson Medical College of Thomas Jefferson University in Philadelphia.
The findings open up the possibility for uncovering other such genetic predispositions for a number of alcohol-related diseases. "Chronic alcoholism is associated with diseases of many organs, such as the liver and the brain - not just the heart," he notes.
Dr. Rubin and his colleagues at the University of Barcelona report their findings September 3 in the Annals of Internal Medicine.
According to Dr. Rubin, between 15 and 40 percent of cases in the Western world of cardiomyopathy, a degenerative disease of the heart muscle, occur in alcoholics. He and his co-workers had previously shown that its occurrence is related to total lifetime intake of alcohol.
In alcoholics who develop cardiomyopathy, the more alcohol they drink, the weaker the heart is, Dr. Rubin explains. The heart's strength is measured by its "ejection fraction," or proportion of blood being pushed out of the heart. Weaker hearts have lower ejection fractions.
"You can attribute about a third of that weakening effect directly to the quantity of alcohol consumed," he says. "So maybe 60 percent or so of the effect is due to something else." Some alcoholics, he notes, can drink a lot and have normal ejection fractions. Others may drink much less, yet they can have hearts that are damaged and perform worse.
Dr. Rubin and his colleagues wondered if genetics contributed to this difference.
They studied 30 Spanish men who were alcoholics and came into a hospital emergency room or clinic in Barcelona with congestive heart failure. The researchers used a questionnaire to find out how much alcohol they drank, in addition to other details about their lifestyle and background. He notes that the group they studied was mostly working class, employed and ethnically similar. They compared these men to 27 alcoholic men who drank as much as the first group did over a lifetime but who had normal hearts.
The researchers looked at the gene for angiotensin-converting enzyme (ACE), which plays a role in hypertension and other cardiovascular conditions. According to Dr. Rubin, a particular form of the gene for the enzyme has been thought to play a role in heart problems.
Dr. Rubin explains that some copies of the ACE gene (genes come in pairs, each called an allele), may contain an extra piece of inserted (I) DNA sequence, while others have a missing, or deleted (D), portion of DNA. The allele with deleted DNA is associated with higher levels of enzyme, and has been linked to cardiomyopathy.
"We showed that those alcoholics who have two copies of the D allele have a 16 times greater risk of developing cardiomyopathy compared to the same individuals who drank just as much but had one copy of the I gene," he says.
Nearly 60 percent of those with heart failure had two copies of the D allele, compared to only three, or 10 percent, of those individuals with heart failure who had two copies of the I allele. Only 7 percent or two cases, had two D alleles among those alcoholics who drank as much but had no cardiomyopathy.
"We don't advise those alcoholics with two I alleles to continue to drink at their current levels," he says. "Some individuals with this genotype did develop cardiomyopathy, so it didn't protect them."
Next, the researchers want to look at other genes that may play a role in alcoholic cardiomyopathy. "We don't know how much the D genotype contributes," Dr. Rubin says. "All we can say right now is if you are an alcoholic and have this genotype, you are at 16 times greater risk for cardiomyopathy."
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Journal
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