C’è UNA BASE GENETICA DELL’ALTA SENSIBILITA’ ?
(Dalla newsletter Comfort Zone della drssa Elaine Aron)
Since the last newsletter, not one but two studies have come out that found certain genes significantly associated with high scores on the HSP Scale. One we knew about, but the other was a surprise. Up until now there was no direct evidence–no specific gene linked to scores on the test–that demonstrated that this trait is innate.
A Serotonin Transporter Gene and High Sensitivity
The first study was done in Denmark and so far has only been presented as a poster at a major conference. It found what the authors and ourselves had predicted, an association between sensitivity and the short allele of the serotonin transporter gene, which I will call the s-allele. “Allele” is another word for a gene’s variations, similar to the variation of left and right handedness. (There are actually three variations–you can have short-short, short-long, or long-long, and sometimes studies are of only of the short-short and sometimes of the short-long–this study only reported on the short-short.) The s-allele causes you to have less serotonin available and so it became linked with depression after the Selective Serotonin Reuptake Inhibitors or SSRIs were found to help alleviate depression. But even though the link was found very inconsistently, for years having the s-allele was seen as nothing but a liability or vulnerability.
Recently that has changed, and I’m pretty sure that is because of the idea of high sensitivity and the obvious argument that too many people have this trait, and too many (about the same percentage even) have the s-allele, for these to exist in the gene pool without any advantages. Hence what we were saying, that the s-allele might be about sensitivity to good or bad environments rather than be about depression itself, began to make sense to others.
Studies of s-allele carriers* have pointed to certain clear benefits of this variation through its combining of emotional reactivity and depth of processing. For example, s-allele carriers in gambling-based decision-making tasks outperformed others because they were more “emotionally risk averse” when there was a low probability of winning, but were emotionally eager to take a risk when there was a high probability. (I’ve always said that we feel that we are not very competitive, another sort of risk, because we only compete when we are fairly sure we will win, and then it doesn’t feel like there was any competition.) Plus s-allele carriers took substantially longer to reflect before making difficult choices. They also performed better on a delayed pattern recognition task and a task requiring recognizing letters in mirrored versus normal form.
Rhesus monkeys also have an s-allele for a serotonin transporter gene and carriers of this allele evidence similar “broadly superior performance,” on a variety of decision-making tasks. (If you click through to the article, skip to the Results or Discussion sections.)
Ten Dopamine Genes and High Sensitivity
The second new genetic study used a very different method, one of looking at essentially all the genes with alleles that affect the dopamine system. Dopamine is the other major neurotransmitter, besides serotonin. I’m not sure why they chose to study it, except that these genes are equally related to the “For Better and for Worse” effect of being responsive to the environment–that is, doing better than others in good conditions and worse than others in bad. The authors explain at the outset of the study that instead of using a familiar trait, such as introversion-extraversion or neuroticism (two of the favorites these days), they chose a trait that they think is “deeply rooted in the nervous system (the Highly Sensitive Personality, HSP).”
Hooray for their insight–and that it worked for them. They found a very surprising number of dopamine alleles associated with the trait. In all, a set of 10 genes predicted a medium to high chance of being highly sensitive. Genetic studies of most personality traits have not found anything close to that, suggesting that sensitivity comes much closer to being a trait that is actually inherited, not just the result of genes interacting with something else. At the moment, the role of these particular dopamine genes is not very well understood, and especially not by me! So I have to study it further.
What Does this Mean for You?
Together these studies provide very direct evidence that sensitivity, or something close to it, is inherited. (I’ll explain “something close to it” below.) First, this is the best answer to those who think we can just get over it. We can’t. “It’s innate.” Second, this innate thing is not basically something we should want to get over. “And besides, it has its many advantages.”
There’s your answer to them. “It’s innate and it has advantages.” What people want for us to get over are the disadvantages, but we can’t and don’t need to and shouldn’t want to or be asked to stop being highly sensitive. Now, reread this paragraph until you can say it, when appropriate, to your critics. (You could even print the studies and hand them out! Except most people would not understand them.)
“Something Close to It”
We cannot know for sure that it is exactly “sensitivity” that is being created genetically. Most personality traits and “styles of behaving” are inherited in some way. In fact, many specific acts are “heritable.” Divorce is heritable, and so is wearing skirts. But that does not mean that there is a Skirt Gene or a Divorce Gene–that is, it does not mean that there is a gene that ought to have that label on it. Genes determining gender, not a Skirt Gene, increase the chances that we will wear skirts.
Commonly studied, heritable personality traits such as Positive Emotionality, Negative Emotionality, and Constraint explained some of the rate of divorce.* That finding takes us a step closer to finding the genetic cause of divorce, in that it has something to do with inherited personality traits, but again, the relationship of the most commonly studied personality traits to any known genetic variation has been low. For example, Negative Emotionality or Neuroticism is highly heritable, yet it has been difficult to identify a gene consistently associated with it. The same is true of extraversion and many other well-known traits.
Again, it seems that sensitivity is proving to be better associated with genes governing personality differences than most other personality traits have. (Sensation seeking is an exception, by the way, and it is another trait that HSPs can inherit.)
However, there are hundreds of genes affecting personality, so there won’t be one sensitivity gene, and the different gene combinations are going to make for different “flavors” of sensitivity. To make matters even more complicated, these genes all interact with each other and the environment: In this study of the genes associated with HS, some of the likelihood of scoring high on the HSP Scale seemed to be determined, at least statistically, by stressful life events at the time of taking the test.
Further, as other researchers catch on to the general idea, they may have other names for the trait, emphasizing certain aspects of sensitivity and wanting to name it for that “something else close to it.” They are already picking apart the HSP Scale (the “self-test”), saying it measures two or three different things, and that might be true in some way. That’s part of the scientific process. The point is that it could turn out that what we call sensitivity could be slightly more accurately called something else. But whatever it is precisely termed in the end, it isn’t a vulnerability to any disorder and it cannot be reduced to any of the already well known traits such as introversion. Sometimes I wish I had started out with “highly responsive,” although I’m not sure it would have made matters clearer, and many fewer people would have recognized themselves in the title The Highly Responsive Person!
This is a scientific journey of exploration and we will have to be patient and go with the flow. But it is something more than science for us. It is our identity now. Fortunately, there is so much variation in the trait’s genetics that if a study says most HSPs have this or that gene or behavior but you do not, you don’t have to worry that you are not really an HSP. You score high on the “self-test,” and that self-test is a pretty close fit with known variations in both the dopamine and serotonin systems. That is, your whatever-it-is-but-sensitivity-for-now innate trait, in whatever quirky way it operates, is real.