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. 

Follow up work is necessary, but “this is encouraging, and suggests we are headed in the right direction,” says study leader, McGill University psychiatrist Marco Leyton.

“There is little debate that some people have a biological predisposition to excessive use and difficulty stopping” alcohol and other drug use, says Sally Satel, a Yale University psychiatrist (uninvolved with the study). She is skeptical of the idea of calling addictions “diseases.” But even she is convinced that biological factors play a role in recovery.

Still, no one has found any reliable biological predictor of alcoholism, outside of some genetic markers involving metabolism of ethanol and nicotine, none of which have yet been found overwhelmingly predictive.

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 not get sleepy, or experience 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, 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 very powerful 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 clearly reflect this fact.

There were “passionate discussions” revolving around this notion last summer when the DSM-5 was being finalized. The topic is highly likely to resurface when the DSM-6 negotiations start, Leyton notes.

In the meantime, much more remains to be done to firmly establish whether PET scans can truly predict the onset of alcoholism. There was, in the current Leyton study, only “some overlap” between people with another standard addition risk-factor trait—reward-seeking tendencies—and people with the aforementioned  “low intoxication response,” for example.

Says Leyton: “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.”

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.