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Nature or Nurture? Questions in Addiction

When we say nature or nurture, what exactly are we asking?

DNA in a hand nature or nuture
DNA in hand on blue background concept design.

Nature or nurture.

It’s a theme humans have explored for generations.

What does it mean?

When we say nature or nurture – what exactly are we asking?

Let’s take an example from somewhere you may not expect: the arts.

The musical and movie “My Fair Lady,” based on the play “Pygmalion” by George Bernard Shaw, is a classic example of our exploration of the nature v. nurture question. In the story, a professor from high English society, Henry Higgins, meets a working-class flower girl, Eliza Doolittle, while out and about London. Circumstances cause their paths to cross again, after which Henry bets a friend that with six months of tutoring in elocution and etiquette, he can teach Eliza – a young woman with a strong Cockney accent, unfamiliar with the norms of high society – to pass as a cultured and refined English lady.

Yes, that’s the same basic plot as the movie “Trading Places” with Eddie Murphy and Dan Akroyd, and asks the same basic questions:

Are we born with qualities and characteristics that determine who we become?

Or, do we learn the qualities and characteristics that determine who we become?

Those who say nature determines who we become believe our dominant personality and behavioral characteristics are locked in at birth, whereas those who say nurture determines who we become believe external factors and circumstances play a more significant role in our long-term development, and therefore, determine the person we eventually become.

In the words of modern medical science, the nature camp believes genetics determine who we become, and the nurture camp believes environment and learning determine who we become.

Nature, Nurture, and Personality Types

What does all this have to do with addiction?

It’s simple – and you’ve probably encountered it before: there are those who believe people are born with certain characteristics that predispose them to addiction, and there are those who believe that environment and upbringing are what drives people toward addiction, rather than the traits they’re born with.

The former are the nature camp, the latter are the nurture camp.

You often hear things like this:

I’ve got an addictive personality,” or, “He has no self-control. If he ever tried drugs, he’d get addicted,” or “She’s been through a lot – I’m not surprised she has a drinking problem.”

First of all, we have to address something right away: the phrase addictive personality is neither a scientific term nor a medical/psychiatric diagnosis. It’s a colloquial term that people use to describe themselves, or others, when they’re looking for a way to explain why or how they developed an alcohol or substance use disorder.

The three sentences above reinforce myths and perpetuate stereotypes that contribute to the ongoing stigma around addiction and addiction treatment – and in 2019, you’ll never hear a mental health professional using sentences like those.

However, they do illustrate the nature v. nurture debate and how it relates to alcohol and substance use disorders. And they give us a chance to transition away from using the terms nature and nurture in favor of words that have medical and scientific relevance:

When someone says nature, what they’re talking about is genetics: the components of their DNA that lead to specific physical conditions and behavioral characteristics. When someone says nurture, what they’re talking about is environment: the components of their lived experience that lead to specific physical conditions or behavioral characteristics. That’s how we’ll talk about this debate for the rest of this article: rather than nature or nurture, we’ll say genetics or environment.

Which leads us to the question that drives this article: what has more influence on whether an individual develops an alcohol or substance use disorder?

Is it genetics?

Or is it environment?

The answer is yes – to both.

Genes + Environment: A Dynamic Interplay

That confounding, possibly annoying answer is the truth: at this point in our knowledge, we know both genetics and environment contribute to the development of alcohol and substance use disorders. We also know that it’s not one or the other: a combination of factors that include genetics and environment lead to disordered use of alcohol and substances.

While we can point to specific genes and say, yes, the presence of those genes correlates with elevated rates of substance use, we can’t say that a person with those genes definitely will develop a substance use disorder. And likewise, while we can point to specific environmental factors and say, yes, the presence of those factors correlates with elevated rates of problem alcohol use, we can’t say that a person exposed to those environmental factors definitely will develop an alcohol use disorder.

If it was that straightforward, we’d tell you right now.

We’d love to make a simple, declarative statement about this topic, but what we can say right now is that the relationship between genes, environment, and addiction is complicated. And we’re right at the beginning of understanding how these factors interact and lead to – or away from – alcohol and substance use disorders.

Therefore, we’ll start with something even more basic than the fact that we’ve associated specific genes with specific behaviors related to alcohol and substance use disorders, as mentioned above. We’ll go back to the very beginning and pose a question that most people think has been settled:

Is the tendency toward developing an alcohol or substance use disorder something that can be passed down from one generation to the next?

The answer: yes.

Next question:

Does that mean that if your mother, father, or grandparents have an alcohol or substance use disorder, you will develop one yourself?

The answer: no.

We’ll explain.

Population-Level Studies

Solid evidence for those answers comes from a study published in 2014 in Sweden. Researchers conducted a Genome-Wide Association Study (GWAS) that included the health and genetic records of more than a million people, and applied a twin sibling model to come to the following conclusion:

  • In males, the hereditability of disordered substance use was 55%
  • In females, the hereditability of disordered substance use was 73%

The researchers then examined the effect of environment on those individuals and found that community-level influences such as drug availability, peer influence, peer deviance, and socioeconomic/neighborhood milieu had a greater effect than household-level environmental influences, such as parent monitoring or the quality of parent-child relationships, on the likelihood that an individual would develop a substance use disorder.

The takeaway from the Swedish study is this: yes, the risk for developing a substance use disorder can be inherited – meaning the risk is genetic – and yes, specific environmental elements can increase this risk – meaning the risk is also influenced by the environment. However, the Swedish study further shows that the combination of elevated genetic and elevated environmental risk factors does not mean an individual definitely will develop a substance use disorder.

That’s why we say the effect of genes and environment on alcohol and substance use disorders is complicated: neither genetic makeup nor environment is wholly determinative. Researchers can identify both genetic and environmental factors that increase risk of disordered substance use, but they’re far from making assertions such as this:

[Gene X] + [Environment Y] = [100% Chance of Substance Use Disorder]

That may happen in the future. For now, a group of scientists from King’s College in London, U.K., have proposed a useful theoretical framework for understanding the combined effect of genetics and environment on the development of alcohol and substance use disorders.

The Stage Sequential Nature of Drug and Alcohol Use

In the 2015 study “Genetic and Environmental Interplay in Adolescent Substance Use Disorders,” researchers offer an example of how we may simplify – or at least codify and streamline – the way we discuss the role genetics and environment play in alcohol and substance use. It’s based on first acknowledging what they call the stage sequential aspect of drug use, i.e. the concept that the path from no substance or alcohol use to an alcohol or substance use disorder happens in a step-wise fashion, then recognizing that at each step, different genetic and environmental factors affect the path of each individual in varying degrees.

Here’s what their model looks like:

Stages of Alcohol/Drug Use, Genes, and Environment

  1. Opportunity. This is the pre-use stage of alcohol and/or drug use. When alcohol or drugs are available, researchers conclude that individual alcohol or drug use is influenced by both genetic and environmental factors.
    1. Genetic Factors: Genes related to novelty seeking and risk taking.
    1. Environmental Factors: Parental monitoring, neighborhood socioeconomic status.
  2. Initiation of Use. This describes the early phase of alcohol or drug use. Researchers identify both genetic and environmental factors that affect the individual experience of alcohol or drug use, which, in turn, has an effect on continued use or cessation of use.
    1. Genetic Factors: Genes related to subjective experience of alcohol/drug use.
    1. Environmental Factors: Availability of alcohol or drugs, community norms around alcohol and drugs.
  3. Continuation of Use. This describes the phase between initiation – the decision to use – and disordered use, i.e. addiction. Again, researchers identify both genetic and environmental factors that influence the transition from initiation or sporadic alcohol/drug use to regular or heavy alcohol/drug use.
    1. Genetic Factors: Genes related to drug/alcohol metabolism.
    1. Environmental Factors: Peer influence, early trauma, i.e. childhood neglect or abuse.
  4. Disordered Use and Treatment. This is the phase of use that used to be called addiction or dependence. We now describe someone in this phase as an individual living with an alcohol or substance use disorder. Little research has been performed with regards to effect of genetics on treatment, while environmental factors related to treatment are well-known.
    1. Genetic Factors: Preliminary evidence suggests that individuals with genes that make them susceptible to early initiation of use are also susceptible to clinical interventions geared toward cessation of use.
    1. Environmental Factors: Family history of treatment, social stigma around alcohol/substance use disorder treatment, socioeconomic factors related to access to effective treatment.

This framework gives health scientists working in addiction research discrete and manageable areas upon which to focus their research. It also allows them to target their work at specific populations, when applicable, and understand what factors are at play for that population during each phase.

For instance, a research team may study the combined genetic/environmental effect on an individual with a genetic risk for elevated novelty-seeking behavior who also experiences an environmental risk factor such as childhood abuse or neglect, and apply that research to the Opportunity stage identified above. Or, a research team may study the combined genetic/environmental effect on an individual who has a genetic risk related to alcohol metabolism but lives in an environment that does not condone alcohol use, and apply the results of that research to the Continuation of Use stage. The combinations are not infinite, but they are numerous, and this framework can help researchers focus their efforts and develop evidence that pharmaceutical companies, doctors, and clinicians can use to create practical treatment and/or prevention applications.

The Future of Treatment

We suspect that some type of gene therapy – or gene-related therapy – will play a role in the treatment of alcohol and substance use disorders at some point in the not-too-distant future, but the complexity of the relationship of genes and environment means we should not expect a silver bullet or attach our hopes for the future of treatment on discovering the one gene that explains it all.

That’s unlikely to happen.

What’s more likely to happen is that as we gather more and more evidence about the complex interactions between genetics and environment, with regards to alcohol and substance use disorders, we’ll be able to create treatment approaches that are tuned more precisely to the genetic and environmental circumstances unique to each individual.

Hypothetically, a clinician developing a personalized treatment plan could tailor a course of treatment to meet the specific genetic and environmental profile of the individual seeking treatment, thereby increasing the likelihood of a positive treatment outcome. The same is true for prevention: an individual with a high genetic risk for experiencing elevated euphoric effects of a drug who also lives in an environment where drug use is common will be able to understand their elevated risk and avoid experimenting with drugs at all, which could reduce their chances of developing a substance use disorder.

As for Eliza Doolittle from “My Fair Lady” – or Eddie Murphy in “Trading Places” – we all know the facts: each human is born with the potential to transcend their environment, but each person is also a product of their environment and upbringing. Each experience we have interacts with our genetic profile to create the person we become. This default truism – which most of us accept – is supported by the research mentioned above.

Which bring us to this conclusion, vis a vis addiction: both nature and nurture – genetics and the environment – play a role in how, why, and when an individual may or may not develop an alcohol or substance use disorder.

Our job now is to work out the details – and apply our new knowledge to help as many people as we can as effectively as possible.

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