At least half of a person's susceptibility to drug addiction can be linked to genetic factors. Presenters at an April 8 congressional hearing outlined new research on the genetic basis for addiction and recommended ways to incorporate those findings into treatment. The hearing was organized by APA's Science Government Relations Office.

Researchers first need to overcome public misunderstanding and distrust regarding genetic testing. That means physicians and the public need to better understand the interactions between genetics and addiction, said Alexandra Shields, PhD, director of the Harvard University/Massachusetts General Hospital Center on Genomics, Vulnerable Populations and Health Disparities. According to a national survey, only 5 percent of primary-care physicians feel confident in their ability to interpret genetic tests, and only 4 percent would feel confident suggesting treatment based on genetics.

There are very good reasons for physicians to pay attention to the impact advances in genetic testing are likely to have on their ability to treat patients, said Nora Volkow, MD, director of the National Institute on Drug Abuse. "Understanding the complex interactions between the factors involved in drug abuse and addiction is critical to their effective prevention and treatment," she said. With new data quickly piling up, physicians might soon be able to incorporate genetic tests in their practice, allowing them to better match specific treatments to individuals.

For example, Volkow explained that the number of a certain type of dopamine receptor, known as D2, might someday be used to predict whether someone will become addicted to alcohol, cocaine and heroin. Brain imaging suggests that people with fewer D2 receptors are more likely to become addicted than those with many of the receptors--and how many of these receptors people have is, in part, genetically determined. Of course, environmental factors also play a role, so propensity isn't destiny, Volkow added. First a person has to experiment with drugs, then he or she has to repeatedly use them. At that point, genetic vulnerability helps determine who winds up addicted.

When it comes to tobacco, genetics account for about 75 percent of a person's inclination to begin smoking, said University of Pennsylvania psychologist Caryn Lerman, PhD. Genes also account for 60 percent of the tendency to become addicted and 54 percent of one's ability to quit.

Because not all smokers are created equal, it's possible to look at genetic factors to determine the best way to quit. The genetically determined speed at which the body can metabolize nicotine, for example, makes a difference as to whether a nicotine patch or a nicotine nasal spray will work better long term.

"A better understanding of biology will help us to personalize treatment to individual smokers," Lerman said.

--M. Price