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    Study links genetic trait to addiction

    The discovery may aid in measuring addiction risks and lead to more effective treatments.

    By WES ALLISON, Times Staff Writer
    © St. Petersburg Times
    published March 20, 2002

    TAMPA -- In the hunt for the powerful forces that drive addictions, researchers say they have definitively linked a common genetic trait to drug and alcohol abuse.

    The discovery, which elaborates on earlier suspicions about a gene called mu-opioid, eventually may help people measure their own risk for addiction, and help scientists design more effective drugs for treating substance abuse.

    The study is published in this month's issue of Molecular Psychiatry. In it, scientists at the University of South Florida and James A. Haley VA Medical Center in Tampa report that 95 percent of study participants who abused alcohol, smoked and used illicit drugs shared a specific variation of the mu-opioid gene.

    In fact, the variation was 50 percent more common among the substance abusers than among study participants who never smoke or drank. And the more addictions the participants had, the more likely they were to have the variation.

    "This is what would be considered a gene for general substance abuse," said Dr. John A. Schinka, the study's lead author and the director of the neuro-psychology clinic at James A. Haley.

    Research has shown that about half a person's likelihood of developing an addiction is based on genetics. Ten to 20 genes may be involved, but only mu-opioid has been confirmed, Schinka said.

    Dr. George Koob, professor of neuropharmacology at the Scripps Research Institute near San Diego and a leading researcher in the field of addiction genetics, said the USF study offers important insight into the genetic factors for substance abuse, especially the notion that one variation of mu-opioid, known as AA, may be responsible for more than just alcoholism.

    "Down the line, if people can find out what makes you vulnerable to addiction, it's going to be the same as what makes you vulnerable to heart disease or hypertension," Koob said. "My family has a history of cardiac disease, so I'm careful about keeping my cholesterol down, and my weight down, and eating right. If we can find markers that tell us if people are vulnerable to certain addictions . . . maybe you would want to be careful about how much you drink."

    Knowing which genes are responsible for addiction also would give researchers potential targets for new medications.

    Taken alone, the mu-opioid variation probably accounts for just 5 percent of a person's risk of drug or alcohol addiction. That may not sound like much. But Dr. David Goldman, chief of the neurogenetics lab at the National Institute of Alcohol Abuse and Alcoholism, noted that "if you isolate 5 percent of the variance for a very common disease, which has a huge public health impact, that 5 percent is worth a lot."

    Roughly 10 percent of men and 5 percent of women are alcoholics.

    The mu-opioid gene expresses itself in one of three variations, known as GG, AG or AA. Everyone is born with one of these variations, but only AA influences addiction. It's unknown what percentage of the general population has the AA type, but it is believed to be quite common.

    Among the control group, about 65 percent had the AA variation. Among the alcoholics, 80 percent had the AA variation. And among those who were or had been addicted to alcohol, drugs and nicotine, 95 percent had the AA variation.

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