People with a gene variant that enhances the brain's response to opioids appear to get a larger "kick" from alcohol than people without this variant, according to new research. In addition, these individuals are much more likely to have a family history of alcoholism.
Alcohol releases natural opium-like chemicals called opioids, which in turn influence the dopamine system. This system, says researcher Kent Hutchison, is involved in cravings and the desire to use alcohol or drugs. "Thus," he says, "it is alcohol's effects on endogenous [naturally occurring] opioids that act as the gateway through which alcohol may influence this system." He notes that children of alcoholics have lower levels of opioids called beta- endorphins than children of non-alcoholic parents, and that young adults with a family history of alcoholism show larger increases in beta-endorphin levels when they drink than peers without such a family history.
To further investigate the role of opioids in alcoholism, Hutchison and Lara Ray studied 20 male and 18 female college students who were moderate to heavy drinkers, dividing them into two groups. One group possessed one copy of the "G" allele (gene variant) of a gene encoding for mu-opioid receptors and one copy of the "A" allele. The other group had two copies of the "A" allele. The G allele causes receptors to bind three times more tightly to beta-endorphins, meaning that a nerve cell with the G allele is much more sensitive to these chemicals.
Hutchison and Ray administered intravenous doses of alcohol to the participants and queried them about their reactions. The researchers found that those with the G allele reported higher levels of intoxication, stimulation, sedation, and happiness when they drank than did those with two A alleles. In addition, they found that individuals with one G allele were nearly three times more likely than those with two A alleles to have family histories of alcoholism.
In separate research, David Oslin and colleagues found that individuals with at least one G allele appear to respond better to treatment with naltrexone, a drug that blocks the effects of opioids, than those without this allele. This makes sense, say Hutchison and Ray, because "a medication that reduces feelings of euphoria after alcohol consumption may be more successful among individuals with a genetic predisposition to greater feelings of euphoria after consuming alcohol."
"A polymorphism of the mu-opioid receptor gene (OPRM1) and sensitivity to the effects of alcohol in humans," L. A. Ray and K. E. Hutchison, Alcoholism: Clinical and Experimental Research, Vol. 28, No. 12, December 2004, 1789-95. Address: Kent E. Hutchison, Department of Psychology, University of Colorado, Campus Box 345, Boulder, CO 80309-0345, KentH@psychology.colorado.edu.
"A genetic difference at the opiate receptor gene affects a person's response to alcohol," news release, Alcoholism: Clinical and Experimental Research, December 14, 2004.