Genetics

Why does it seem as if some families have an unlucky streak of alcoholism and other substances and even behavioral addictions that plague more than just one or two of their relatives?  Why do some people have an easier time when they try to stop drinking or smoking than others do?  Why are some people able to experiment with drugs without getting hooked while others become addicted after only a few encounters?  From clinical observations, physicians and scientists have long suspected that there is a genetic component to addiction, yet they have only recently been able to identify specific genes that can be implicated in the complex phenomenon that is addiction.  Addiction cannot be linked to a single gene; rather, vulnerability to addiction arises from the interactions of many genes.  Although studies have shown that genetics is a very important factor in addiction, other factors, including environmental triggers (like stressful situations) and a history of mental illnesses like depression or post-traumatic stress disorder, are also highly influential.  An understanding of genetics as well as the other risk factors can help you to gauge your likelihood of being vulnerable to addiction, but neither your genetic makeup nor your life situation can destine you to a life of addiction.

How do scholars study the genetics of addiction?

One method that scientists use to identify the genetic components of addiction is by studying families in which a large number of members are addicted to a certain substance.  (You can read more about inter-generational behavioral patterns of addiction in Legacy of Addiction: How Behaviors Are Transmitted Over Generations.) Scientists compare the DNA of family members who are addicted with the DNA of family members who are not addicted in order to identify genes that are potentially involved in addiction in general or addiction to the specific substance in particular.  Studies of identical twins and adopted children have also yielded lots of information about inherited traits.  In addition, researchers use animal models, including mice and fruit flies.  Because drugs act on the reward pathways in both mice and people in similar ways, scientists can learn a lot by selectively breeding mice to exhibit certain types of addictive propensities, including a preference for certain types of drugs, specific withdrawal symptoms, and tolerance levels. 

What genes have been linked to addiction?

Here are a few examples.  Scientists have discovered that a variation of the dopamine receptor gene DRD2 (the so-called “pleasure-seeking gene”) is more likely to be present in people who are actively struggling with or who have struggled with alcohol, cocaine, amphetamine, and nicotine addictions.  Another gene, CYP2A6, is more frequently found in non-smokers; it seems to protect them from nicotine addiction by giving them feelings of nausea and dizziness when they smoke.  A variant in a nicotine-receptor gene has been found to both double the risk for nicotine addiction and increase the risk for lung cancer.  Another recent study demonstrated that variations in the COMT gene can predict how likely it is that an individual who has been exposed to marijuana at an early age will develop mental illness later in life.  In laboratories, mice have been bred to have a diminished reward response to morphine and cocaine, to exhibit less severe withdrawal symptoms when taken off of barbiturates, and to drink three times the amount of alcohol as a normal mouse would.

Can genetic testing be used to predict whether or not a baby will become an addict in adulthood?

Because addictions result from the complex interactions among multiple genes, influences from the environment, and personal choices, it is not really possible or ethical to attempt to predict from a DNA test whether or not a baby will become an addict.

How can genetic research help treat and prevent addiction?

Researchers hope that understanding the distinctive genetic makeup of individuals will help physicians design more effective, personalized treatment plans.  Genes affect how individuals’ brains respond to certain illicit drugs and medications, as well as how their bodies metabolize these chemicals.  For instance, one study found that naltrexone, a drug used to treat alcohol addiction, was much more effective in preventing relapse for individuals who had a particular variant in an opioid receptor gene.  Knowing which genetic variants an individual possesses may help doctors prescribe uniquely targeted and, by extension, more effective medications in the future.  In addition, when researchers can directly identify addiction genes, they then also have the opportunity to develop pharmacological solutions that specifically target these genes, in the hopes of restoring normal neural functioning to the brain.