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The Sensitivity Gene

“It’s got nothing to do with environment. With his genes, you could put him anywhere and he’d come out on top. Breeding, same as in race horses. It’s in the blood.”
–Mortimer Duke, Trading Places

Jerome Kagen, Harvard

For years, scientists have been trying to trace the genetic relationship of certain mental conditions. People have long had an inkling, for example, that depression has a hereditary component. They’ve also believed this about anxiety disorders and other kinds of neurosis.

The answers to these genetic questions can be controversial, because they make statements about our identities – either reinforcing or threatening preexisting narratives. Let’s say that there was a single gene that predisposed you to depression. Does that mean you’re destined to live with the disease? Does that status make an irrevocable statement about who you are and who you’ll always be? Would this understanding make you more or less likely to seek treatment? As a society, would we stop trying to address other known contributors to depression – like abusive households – in favor of emphasizing pharmaceutical remedies?

Recently, some exciting new research has come to light showing linkage between genetically-defined brain chemical transporters and personality attributes. Scientists have known for a while that brain chemicals like dopamine and serotonin affect mood and disposition. This research takes that relationship one step further, linking a personality trait with certain, specific genetic markers.

I first saw reference to this area in Susan Cain’s book, Quiet: The Power of Introverts. I then read several more related studies and essays by the scientists who originated the research. One of the leading scientists in this field is Jerome Kagen out of Harvard, but many other recent studies have carried this research forward.

Chromosome 17 of the serotonin transporter gene

This area of research concerns a serotonin-transporter gene 5-HTTLPR. Originally, scientists identified two variants of this gene, the long (“L”) allele and short (“S”) allele. A third variant has since been identified, but I will still refer to them as L and S for simplicity. These scientists have discovered that people carrying the short allele of the 5-HTTLPR gene show greater reactivity to stimuli in the amygdala (threat-center of the brain) than do those who carry the long allele. Short-allele subjects have been found to be more sensitive and more reactive to the world around them, especially in social contexts or perceptions of threat.

Because of this heightened sense of reactivity, Kagen “hypothesized that infants born with an especially excitable amygdala (i.e. short-allele children) would…grow up to be children who were more likely to feel vigilant when meeting new people” (Cain, Quiet). In other words, high-reactivity may predispose one to guarded and reclusive behavior. Researchers refer to this as behavioral inhibition. Cain points out that this is one possible biological route to having an introverted temperament.

Introversion, however, is far from the only possible outcome. Depending on which environmental factors come into play, short-allele subjects have correlated with both above-average and below-average levels of anxiety, depression, and delinquency. Short-allele children raised in stable, supportive environments tend to show more resilience to depression, anxiety and even illness. However, short-allele children raised in stressful environments tend to succumb more often to these factors. The current consensus hypothesis is that short-allele (highly-reactive) children are more “malleable – for worse, but also for better,” as one researcher puts it.

This tendency to high- or low-reactivity has implications in broader principles of psychology. Here’s an example. In a previous blog article, we discussed Dr. Mark Leary and Sociometer Theory. That theory suggests that self-esteem is not a trait-in-a-vacuum, but rather a personal evaluation of your own worth relative to your social group. People take external feedback from others, and use that to influence their own idea of themselves. This serotonin transporter research might suggest that some of the population would be more sensitive to social feedback, and bring to to bear more harshly upon their own self esteem.

Kagen is quick to point out that “more instances of academic failure, conduct disorder, delinquency, substance abuse, anxiety disorder, and depression are traceable to the education and income of the person or their family of rearing than to a particular allele or set of alleles.” He writes about his concern that there is much more interest in, and funding for, genetic behavioral explanations rather than societal explanations. This passage is from his 2007 essay, A Trio of Concerns:

The current ideology is so entrenched it is difficult to persuade state or federal legislators to allocate public funds for the prevention of psychopathology if they are told that neglect, poverty, and abuse place children at risk for the development of symptoms of anxiety, anger, or depression. However, these same legislators become enthusiastic advocates of prevention if they are told that these same environmental conditions alter children’s brains (Shonkoff, personal communication, October 2006). Apparently, the latter description implies that the consequences of early experience are permanent. Descartes’ unfortunate division between soul and body is alive and well in the ideology of most citizens. The current emphasis on the biological contributions to psychological outcomes has the disadvantage of inviting a conceptualization of social interventions or therapeutic regimens as pills for an organic condition.

As we noted in the beginning, the danger of exploring this kind of science is that it reinforces the notion that questions of identity, disposition and societal problems are all answered through biology. That is why responsible scientists are quick to qualify their findings, and to cite the intervening social and environmental factors involved in the correlation.

For my part, I remember feeling a great deal of relief when I read about this research, and I think it has the potential to help a lot of people gain better self-knowledge. If you notice that you have a certain sensitivity to the world around you, and that you feel uncomfortable in certain situations or with certain activities, you might be tempted to wonder what your problem is. You might wonder why you haven’t outgrown that tendency. You might wonder what you have to do to overcome that sense of hesitation, and get with the crowd. There’s a lot of power in knowing that your brain is reacting the way that it is through no fault of your own. Now, when you begin to feel those stresses, you can simply recognize that heightened sensitivity is just part of the natural workings of your brain, and take that into account in decisive situations. For many people, I believe that knowledge would be very freeing.

In the coming years, a great deal of knowledge will come from the study of genetics. This will enhance our scientific capabilities, but it will not, on its own, solve the complicated societal and psychological problems that we still have yet to address. We must be judicious about using this research for greater self-knowledge rather than trying to find easy fixes to hard problems.

  1. Deb R
    August 20, 2012 at 6:59 PM

    Often our genetic gifts have burdens, but blessings as well. If you are “wired” to be more sensitive, this gives you more data points on which to base decisions. According to the book, “The Emotionally Intelligent Manager: How to Develop and Use the Four Key Emotional Skills of Leadership” by David R. Caruso and Peter Salovey, people who carry gene linked to sensitivity may be better at making complex decisions, especially ones that can carry big gains or big losses. Sensitivity is a bonus for performers and speakers, with more of an ability to read and empathize with an audience and reach them more effectively.

    Genetics certainly isn’t the be all end all of personality and behavior, but greater understanding of the predispositions of such can help us towards greater self-understanding and empathy with others.

  1. October 31, 2012 at 4:54 PM
  2. August 29, 2014 at 4:27 PM

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