FEATURE ARTICLE
Predicting Addiction
Behavioral genetics uses twins and time to decipher the origins of addiction and learn who is most vulnerable
Lisa Legrand, William Iacono, Matt McGue
Markers of Risk
Personality. Psychologists can distinguish at-risk youth by their personality, family history, brainwave patterns and behavior. For example, certain personality traits do not distribute equally among addicts and nonaddicts: The addiction-vulnerable tend to be more impulsive, unruly and easily bored. They're generally outgoing, sociable, expressive and rebellious, and they enjoy taking risks. They are more likely to question authority and challenge tradition.
Some addicts defy these categories, and having a certain personality type doesn't doom one to addiction. But such traits do place individuals at elevated risk. For reasons not completely understood, they accompany addiction much more frequently than the traits of being shy, cautious and conventional.
Although these characteristics do not directly cause addiction, neither are they simply the consequences of addiction. In fact, teachers' impressions of their 11-year-old students predicted alcohol problems 16 years later, according to a Swedish study led by C. Robert Cloninger (now at Washington University in St. Louis). Boys low in "harm avoidance" (ones who lacked fear and inhibition) and high in "novelty seeking" (in other words, impulsive, disorderly, easily bored and distracted) were almost 20 times more likely to have future alcohol problems than boys without these traits. Other studies of children in separate countries at different ages confirm that personality is predictive.
Family Background. Having a parent with a substance-abuse disorder is another established predictor of a child's future addiction. One recent and intriguing discovery from the MCTFR is that assessing this risk can be surprisingly straightforward, particularly for alcoholism. The father's answer to "What is the largest amount of alcohol you ever consumed in a 24-hour period?" is highly informative: The greater the amount, the greater his children's risk. More than 24 drinks in 24 hours places his children in an especially risky category.
How can one simple question be so predictive? Its answer is laden with information, including tolerance—the ability, typically developed over many drinking episodes, to consume larger quantities of alcohol before becoming intoxicated—and the loss of control that mark problematic drinking. It is also possible that a father who equivocates on other questions that can formally diagnose alcoholism—such as whether he has been unsuccessful at cutting down on his drinking or whether his drinking has affected family and work—may give a frank answer to this question. In our society, episodes of binge drinking, of being able to "hold your liquor," are sometimes a source of male pride.
Brainwaves. A third predictor comes directly from the brain itself. By using scalp electrodes to detect the electrical signals of groups of neurons, we can record characteristic patterns of brain activity generated by specific visual stimuli. In the complex squiggle of evoked brainwaves, the relative size of one peak, called P300, indicates addiction risk. Having a smaller P300 at age 17 predicts the development of an alcohol or drug problem by age 20. Prior differences in consumption don't explain this observation, as the reduced-amplitude P300 (P3-AR) is not a consequence of alcohol or drug ingestion. Rather, genes strongly influence this trait: P3-AR is often detectable in the children of fathers with substance-use disorders even before these problems emerge in the offspring. The physiological nature of P300 makes it an especially interesting marker, as it may originate from "addiction" genes more directly than any behavior.
Precocious Experimentation. Lastly, at-risk youth are distinguished by the young age at which they first try alcohol without parental permission. Although the vast majority of people try alcohol at some point during their life, it's relatively unusual to try alcohol before the age of 15. In the MCTFR sample of over 2,600 parents who had tried alcohol, only 12 percent of the mothers and 22 percent of the fathers did so before the age of 15. In this subset, 52 percent of the men and 25 percent of the women were alcoholics. For parents who first tried alcohol after age 19, the comparable rates were 13 percent and 2 percent, respectively. So, what distinguishes alcoholism risk is not whether a person tries alcohol during their teen years, but when they try it.
In light of these data, we cannot regard very early experimentation with alcohol as simply a normal rite of passage. Moreover, drinking at a young age often co-occurs with sex, the use of tobacco and illicit drugs, and rule-breaking behaviors. This precocious experimentation could indicate that the individual has inherited the type of freewheeling, impulsive personality that elevates the risk of addiction. But early experimentation may be a problem all by itself. It, and the behaviors that tend to co-occur with it, decrease the likelihood of sobriety-encouraging experiences and increase the chances of mixing with troubled peers and clashing with authority figures.
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