Alcohol: The Genetic Puzzle (3 of 3)

What about other drugs?

Do the same genetic relationships demonstrated in the alcohol adoption studies prove true for other drugs? Was it conceivable that heroin addiction or cigarette smoking could be traits (disorders, really) that men and women inherited?

“There have been a number of animal studies showing genetic differences in sensitivity to nicotine,” said Dr. Neal Benowitz of the Clinical Pharmacology Unit at San Francisco General Hospital, one of the nation’s premier nicotine research centers. And Professor Ovide Pomerleau, the Director of Behavioral Medicine at the University of Michigan Medical School, who collaborated with Cloninger’s group on genetic studies of nicotine and alcohol, told me: “Some people are drawn to smoking, and some people are not. Everybody pretty much goes through the same kind of peer pressures, the same kind of socialization pressures, and then you have some people who emerge as smokers, and some people who don’t. Some people who start smoking give it up easily, and there are others who can’t. Well, why? My answer is that I think there are innate differences in susceptibility.” 

The Cadoret group looked into the question and reported in the Archives of General Psychiatry that alcohol problems in biological relatives appeared to correlate highly with drug abuse in siblings. “Some theorists have suggested that multiple addictions to a wide variety of substances constitute evidence against a genetic interpretation of addiction,” wrote Cadoret. “The present data appear to refute that position, suggesting instead some underlying biochemical foundation involved in all of the substances abused….” 

Dr. Janice Keller Phelps, the drug treatment specialist from Seattle, maintained that “a large number of addicted people I have treated over the years had strong family histories of addiction. Time and again I encountered heroin addicts, cocaine addicts, or speed addicts with one or both parents addicted to alcohol, for example, or with one or more brothers or sisters also addicted—though not necessarily to the same drug. It is known and acknowledged that many alcoholics have one or more alcoholic parents; the large number of children of alcoholics who are not alcoholic but instead are addicted to other substances, however, is not so well recognized.”

In many ways, the genetic findings by Goodwin, Cloninger, and others were as far from the old problems-in-living approach, the Freudian approach, as it was possible to get. As Dr. Edward Sellers, who directed the psychopharmacological research program at the University of Toronto’s Addiction Research Foundation during the 1990s, explained to me: “One simplified way of looking at it is that every cell, every hormone, every membrane in the body has got genetic underpinnings, and while many of the genetic underpinnings are similar in people, in fact there are also huge differences. So on one level, the fact that there is a genetic component to addiction is not very surprising. What is surprising is that you could ever have it show up in a dominant enough way to be something that might be useful in anticipating risk.”

If there existed a set of genes that predisposed people to alcoholism, and possibly other addictions, then these genes had to control the expression of something specific. That’s what genes did. 

However, addiction researchers could not even agree on the matter of where they should be looking for such physical evidence of genetic difference. In the brain? Among the digestive enzymes? Blood platelets? A gene, or a set of genes, coding for…what? Substance H? Production of certain neurotransmitters? What was it they were supposed to be looking for?

What set of genes coded for happiness?

Adapted from The Chemical Carousel: What Science Tells Us About Beating Addiction by Dirk Hanson © 2008.

Graphics Credit: http://www.drugabuse.gov

If the Genes Fit....

U.K psychiatrists agree addiction is "genetically determined."

Although the verdict is very little in doubt these days, the heritability of addictions was reaffirmed by the U.K.'s Royal College of Psychiatrists in London on July 4th.

In a presentation at the group's annual meeting, held at Imperial College, Professor Wim van den Brink of the University of Amsterdam's Academic Medical Center pinned the blame for addiction squarely on the absence of a sufficient number of dopamine receptors in the brain. "Addicts find it difficult to receive pleasure," he said. "They are not likely to enjoy most of the ordinary things most of us enjoy... they are looking for more stimulus."

Professor van den Brink also made clear the importance of environmental interactions for gene expression: "You might start off smoking or taking cocaine, and that first introduction is very much determined by your environment. But to stick with it and become dependent on it is genetically determined."

The self-defeating nature of addiction is graphically illustrated by the overall decrease in the number of pleasure receptors for dopamine and serotonin over time, as drug use escalates. Moreover, addicts show a striking deficiency in the ability to engage in long-term thinking. This behavioral link, the Royal College maintained, is the reason addicts fail to realistically differentiate between short-term pleasure and long-term negative effects.

This inability of drug addicts to engage in effective long-term thinking is well summarized in the old Reverend Gary Davis song: "Cocaine's for horses and it's not for men/Doctor said it kill you, but he didn’t say when."

Photo Credit: National Institute on Drug Abuse

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