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
Minnesota Twins
We have been able to answer some of these questions by examining the life histories of almost 1,400 pairs of twins. Our study of addictive behavior is part of a larger project, the Minnesota Center for Twin Family Research (MCTFR), which has studied the health and development of twins from their pre-teen years through adolescence and into adulthood. Beginning at age 11 (or 17 for a second group), the participants and their parents cooperated with a barrage of questionnaires, interviews, brainwave analyses and blood tests every three years. The twin cohorts are now 23 and 29, respectively, so we have been able to observe them as children before exposure to addictive substances, as teenagers who were often experimenting and as young adults who had passed through the stage of greatest risk for addiction.
Studies of twins are particularly useful for analyzing the origins of a behavior like addiction. Our twin pairs have grown up in the same family environment but have different degrees of genetic similarity. Monozygotic or identical twins have identical genes, but dizygotic or fraternal twins share on average only half of their segregating genes. If the two types of twins are equally similar for a trait, we know that genes are unimportant for that trait. But when monozygotic twins are more similar than dizygotic twins, we conclude that genes have an effect.
This article reviews some of what we know about the development of addiction, including some recent findings from the MCTFR about early substance abuse. Several established markers can predict later addiction and, together with recent research, suggest a provocative conclusion: that addiction may be only one of many related behaviors that stem from the same genetic root. In other words, much of the heritable risk may be nonspecific. Instead, what is passed from parent to child is a tendency toward a group of behaviors, of which addiction is only one of several possible outcomes.
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