A possible biomarker that may identify potential alcoholics—before they ever become alcoholics—has been found in a new study.
The biomarker: a surge of the native chemical dopamine in the brain, viewed via a PET (Positron Emission Tomography) scan, when at-risk people drink.
"This is fascinating," says Wake Forest University addiction neurobiologist David Friedman, who was not involved with the study. "It puts us into biological territory. It says that if you have a big dopamine response to alcohol, you are at greater risk of becoming an alcoholic than if you don't. This is something people have been looking for forever."
“It is encouraging, and suggests we are headed in the right direction,” agrees the study's leader, McGill University psychiatrist Marco Leyton.
Until now, no one has found any reliable biological predictor of alcoholism, outside of some genetic markers, none of which have yet been found overwhelmingly predictive. Multiple genes have been implicated in minor ways, some impacted by the environment, some not, Friedman says. "It has been complicated."
In this latest study, 26 young healthy social drinkers, some of whom possessed standard alcoholism risk factors, were given either the same alcohol doses, or placebos, while in a PET scan. The standard risk factors included alcoholic family members, some alcohol use problems, and “low subjective intoxication responses.” The latter, says Leyton, means the tendency to avoid getting sleepy, and to avoid other negative physical sensations, when drinking a little.
PET scans in Leyton’s study revealed that those with the above standard risk factors experience a surge of dopamine when they drink.
Dopamine, a neurotransmitter chemical housed in the brain, has been implicated in numerous compulsive reward-seeking behaviors. Indeed, many addictions can occur together. A Journal of Studies on Alcohol and Drugs paper out next month, for example, finds alcoholism and eating disorders often occur together and can appear to be genetically linked.
Likewise, a Journal of the American Medical Association Psychiatry study, out this month, finds that many “externalizing disorders” can occur together, from substance abuse to antisocial behaviors. This can be highly genetic (between biologic parents and children), although non-related siblings can exhibit similar co-dysfunctions.
Leyton’s is the first study to look for and find dopamine surges in the brain’s striatum prior to the onset of alcoholism. “The subjects were not alcoholic at the time of testing, but the high-risk ones, by definition, were at elevated risk for developing an alcohol addiction,” he says. “Dopamine surges might increase susceptibility to a wide range of exciting, risky, impulsive behaviors. The exact expression of that predisposition could depend on various factors, such as drug availability, parental models, childhood trauma, etc.”
Leyton believes strongly that alcoholism, and other addictions, are diseases. Genetic proclivities entirely aside, alcohol and other addictive substances can both physically affect, and alter, the brain in critical ways, he says. He and others have been lobbying to get the bible of the psychiatric community, the Diagnostic and Statistical Manual of Mental Disorders (DSM), to more concisely reflect this by categorizing various addictions, not just as diseases (as they are now), but as "externalizing disorders."
There were “passionate discussions” about this last summer when the DSM-5 was being finalized. Thanks to the new study, the topic is likely to resurface in a more concrete, crystalized fashion when the DSM-6 negotiations start, Leyton and Friedman agree.
In the meantime, more remains to be done to firmly establish exactly which psychiatric tests firmly correlate with the PET scans. Friedman and others are excited because the new study validates some psychiatric tests in unprecedented ways. But there was only “some overlap” between people with another standard addition risk-factor trait—reward-seeking tendencies—and people with the aforementioned “low intoxication response,” Leyton says. “It will take more work to delineate more fully dopamine's contribution: maybe mostly to one feature, maybe to both, maybe to some separate feature that overlaps with these two traits.”
But "knowing there is a biological marker behind some of these tests will make them more powerful," says Friedman. "It is a validation."
Leyton’s dopamine/PET scan study, called “Differential Striatal Dopamine Responses Following Oral Alcohol in Individuals at Varying Risk for Dependence,” will be published in the journal Alcoholism: Clinical and Experimental Research in January, 2014.