Behavioral Genetics and The Future of Personalized Medicine

Dr. Nathan Gillespie

This article was written in collaboration between COBE and Dr. Nathan Gillespie, an addiction genetics researcher at the Virginia Institute of Psychiatric and Behavioral Genetics.

In the not too distant future, most people will likely have their genome sequenced and available to them on a thumb drive or a smartphone app. Along with that information, one would answer a series of questions related to their behavior and background. Using statistical models and formulas built off of years of substance use studies, the app would compile the data and inform a person about their risk profile for different health outcomes.

But this isn’t a conversation about destiny or dystopia. This is the future of personalized substance use prevention programs and similar interventions for other disorders powered by genetics research.

So where did this all begin? And where do we stand with this research currently? Let’s start with a few basic questions.

Are you similar to your siblings because you have the same parents or because you grew up in the same environments? Do your genes and your environments interact with one another to influence who you become as an adult?

Behavioral genetics exists at the intersection of psychology and genetics to study how genes and environments interact and influence the similarities and differences between people. Of the many things studied in addiction genetics, the branch of behavioral genetics that focuses on substance use disorders, some of the core questions include:

“To what degree is a given behavior influenced by genes and environment?”

“Do multiple behaviors, disorders and diagnoses share a common cause or set of risk factors?”

“What specific genes influence a given behavior or disorder?”

To answer these questions, researchers often focus on twins. An investigator will typically start with a large population-based sample of twins (500 or more twin pairs, distributed between identical and fraternal twins). Then the rest of these study follows a traditional, survey-based format.

Researchers begin each survey by asking questions you’d see in any standard psychology questionnaire: demographics, family history, behavioral measures, personality traits, etc. After gaining background knowledge questions will shift in focus to psychiatric criteria from the DSM related to substance use disorders. During this part of the survey, researchers ask when someone first used a given substance, when they started using the most, if they stopped, when they stopped and if they ever experienced withdrawal or cravings.

If a large enough population of twins provide that data, then a scientists can use complex mathematical equations and statistics to estimate how much of a given criteria, syndrome or disorder is due to genes or environments.

Based on these studies, behavioral geneticists learned that across all licit and illicit substances, genes appear to explain anywhere between 40 and 70% of individual differences between people. Which means that on average genes account for half of the variation in both risk of initiating and risk of progressing through use to abuse and dependence.

Beyond genes, the majority of the other half of a person’s overall risk is explained by aspects of the environment that are unshared between individuals, meaning random things that happen to you and not to other members of your family. Cultural environmental factors shared within families like where you grew up, your schooling, etc. account for up to 10% of one’s risk of initiating substance use, but have a non-significant effect on one’s risk of progressing from use to abuse.

So how can people use this information to benefit themselves and others?

It would be revolutionary for everyone to know about their ancestral, genetic and environmental background and have that accessible to them before they decide to smoke their first cigarette or drink their first drink. But this kind of prevention programming will only work if the end users are educated. At this stage, if you were to give every individual in the US their risk profile, most wouldn’t know what to do with it. Many would assume, “I have a particular gene on a particular chromosome. Therefore, I’m going to get disorder X or disorder Y.” Often that is not the case.

In most instances, geneticists study complex traits or outcomes which are highly polygenic, meaning a person must have a number of different genes in order to manifest a given problem. Everyone’s genes are different, so everyone has a different mixed bag of risk profiles that interact with one another and influence their health outcomes. So when we discuss genetics and substance use, we should always be careful to talk in probabilities and promote overall literacy in science through genetic counseling and translating research into accessible forms of media.

As researchers and advocates we believe that knowledge is power, and the future of substance use research will open up a great wealth of personalized data about how genes and the environment influence health. But knowledge by itself is not enough: we must all actively promote scientific literacy to apply this new wealth of information to support the common good.