It compared genetic variants from nearly 15,000 individuals diagnosed with alcohol dependence to nearly 38,000 people without such a diagnosis.
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An international team of researchers have identified a gene known to affect the risk for alcohol dependence, and determined many other genes which contribute to the risk to a lesser degree.
The researchers linked genetic factors associated with alcohol dependence to other psychiatric disorders, such as depression, and showed that genetic factors tied to typical drinking sometimes are different from those linked to alcohol dependence.
The study involved more than 50,000 people. It compared genetic variants from nearly 15,000 individuals diagnosed with alcohol dependence to nearly 38,000 people without such a diagnosis.
The one gene that stood out, called ADH1B, regulates how the body converts alcohol to a substance called acetaldehyde. Variants in the gene speed the conversion to acetaldehyde, a compound linked to unpleasant side effects from drinking, and that compound has a protective effect, making people less likely to drink heavily or become alcoholics.
The researchers found that the genetic risk factors related to alcohol dependence also were linked to risk for other psychiatric disorders, such as depression, schizophrenia, ADHD and the use of cigarettes and marijuana.
A key aspect of the study is that it included genetic data from 46,568 European people and 6,280 people of African ancestry. Although the same ADH1B gene was linked to alcoholism risk both in people of European ancestry and African ancestry, the researchers found that different variants in the gene altered risk in the two populations.
The researchers also found that the genetic factors related to simply drinking alcohol were a little different from the genetic factors that contributed to alcohol dependence. In other words, at least at the genetic level, there's a difference between simply drinking alcohol, even large amounts of alcohol, and becoming dependent on it.
"People suffering from alcohol dependence generally drink a great deal, but they also experience other problems related to their drinking, like losing control over when and how much they drink," said senior author Arpana Agrawal, a professor of psychiatry at Washington University School of Medicine in St. Louis.
"I think it's likely that as the sample sizes of our studies increase, we may find new DNA variants related to these problematic aspects of alcohol dependence but possibly not related to typical drinking" Agrawal said.
"The risk conferred by the ADH1B gene is one of the strongest single-gene effects seen in people with a psychiatric illness, but overall, it explains only a small proportion of the risk," Agrawal said. "Many additional gene variants are making small contributions to alcoholism risk, but to find them, we'll need to study more people."
The researchers plan to continue investigating those links between genetic susceptibility to alcohol dependence and risk for other types of psychiatric illness.
It is estimated that one in eight Americans suffers from alcohol dependence.
The study was published online Nov. 26 in the journal Nature Neuroscience.