Genetics of emotions - ADNTRO

Genetics of emotions

What are emotions?

Although emotions are abstract and subjective concepts, through methodical observation and the application of the scientific method it has been possible to draw interesting conclusions about them. The first to do this was Charles Darwin in 1872, by publishing his well-known book The expression of emotions in man and animals, where he describes the main expressive actions in humans and other animals and relates them to a series of emotions (fear, suffering, etc.) that he classifies as universal.

Much has been studied and written since Darwin laid the foundations for what would later become modern psychology. Some more modern definitions of emotions establish that they are psychophysiological reactions that represent modes of adaptation to certain stimuli perceived by an individual. Another common definition states that an emotion is a complete psychological state that involves three distinct components: a subjective experience, a physiological response, and a behavioral or expressive response.

If defining emotions is a complex task, classifying them is even more so. In 1972, psychologist Paul Eckman postulated the existence six basic emotions, understanding as basic those that appear from the moment of birth and that are universal throughout human cultures. These emotions are: fear, disgust, anger, surprise, happiness and sadness. However, there are lists that collect up to 250 different emotions, arising from the six basic emotions previously mentioned.

Are emotions conditioned by genes? Do they present any degree of heritability?

The fact that environmental factors, such as education, sociocultural level, etc. they significantly influence the development of different emotions. However, one might wonder if there is a genetic component that predisposes you to experience certain emotions more intensely than the majority of the population, or that, on the contrary, reduces or inhibits the expression of these emotions.

To answer these questions, we will select the most analyzed and studied basic emotion to date: happiness, and we will review published studies that attempt to resolve the issue of the heritability of happiness.

There is an experiment that is especially interesting, since it was carried out from Identical twins separated at birth and raised in different environments. For our purpose, this is the perfect population sample, since identical twins have exactly the same DNA, the same three billion base pairs, but being raised separately, they are exposed to different environments, which allows us deduce that the aspects of personality and emotions they share will be due at least in part to genes. Through the performance of tests, different personal characteristics (such as the degree of intelligence) and emotional characteristics (such as the feeling of well-being) of the twins separated at birth were measured and surprising coincidences were observed, therefore attributed to their shared genetics. All this allowed show that happiness presents an heritability significant. 

Genetic variants associated with happiness

Although studies with twins separated at birth and raised in different environments have shown that there is a certain degree of heritability in happiness, at this point, one might wonder what genetic variants are associated with this magnificent emotion.

To try to answer this question, again there are several studies that shed light on the subject. The structure and methodology of this type of study is similar in all cases: first a study sample of n participants is taken (the larger it is, the higher quality the study will have), then the level of subjective well-being is measured through questionnaires (which explore how a person perceives their life, the degree of life satisfaction, etc.) and finally GWAS studies are carried out, which allow identify predominant genetic variants in subjects with high subjective well-being.

In 2014, the magazine Journal of Affective Disorders published a work carried out with a sample of 445 people, in which the tendency to gratitude and forgiveness was measured through a questionnaire. Subsequently, a genetic variant was identified in the gene sequence COMT, consisting of a substitution of the amino acid Valine for the amino acid Methionine at position 158 (Val158Met). This variant was predominant in the subjects who, according to the test, showed a greater tendency to gratitude and forgiveness, (which in turn implied a higher level of personal well-being and a lower level of depressive symptoms). In this way, the presence of the variant Val158Met was associated in the gene COMT at a high level of subjective well-being.

Of all the experiments carried out to identify genes related to happiness, the most extensive and impressive was published in 2016 by the magazine Nature Genetics, and it was carried out on a sample of 298,420 people. As always, their level of subjective well-being was measured through questionnaires, a GWAS study was conducted and the existence of 3 SNPs was detected (rs3756290, rs2075677 and rs4958581 in the genes RAPGEF6, CSE1L and NMUR2, respectively) directly related to subjective well-being.

Finally, a study published in 2016 by the journal Frontiers in Human Neuroscience carried out on a sample of 243 white university students allowed to identify the presence of a SNP (rs3796863) in the gene sequence CD38, in charge of controlling the release of oxytocin. It was observed that individuals whose genotype coincided with the previously mentioned SNP showed intense feelings of alienation from parents and peers, as well as increased suicidal tendencies. Therefore, this genetic variant could be associated with lower levels of personal well-being and happiness.

Molecular mechanisms underlying the genetic variants associated with happiness

Once the fact that there are genetic variants that predispose to a higher level of personal well-being and happiness has been established, the second question we ask ourselves is What are the molecular mechanisms that determine that carriers of these variants are happier?

Continuing with the examples of the two previously mentioned studies in which genetic variants associated with a high level of well-being are located, the first one identified a genetic variant in the gene sequence COMT, and in the second a genetic variant was identified in each of the genes RAPGEF6, CSE1L and NMUR2. At the moment there are no more data on the biological mechanisms that determine that carriers of these variants have a better perception of emotional health. However, taking into account the role of the gene in which the variants in question are found, or the tissues in which that gene is expressed, we can begin to conjecture and hypothesize.

The Gen COMT encodes for catechol O-methyltransferase, one of the many enzymes that degrade catecholamines (such as dopamine, epinephrine, and norepinephrine) in humans. Intuitively, we might think that a genetic variant of the gene COMT it could imply a lower degradation of catecholamines, and therefore a greater sensation of subjective well-being. However, the case of genes RAPGEF6, CSE1L and NMUR2 it is less clear. They have been observed to be expressed in the brain, but also in the pancreas or adrenal glands. Thus, it is believed that the genetic variants detected could modify the normal function of hormone-producing tissues, thus modulating various aspects, such as the response to anxiety and stress, and therefore the level of subjective well-being and happiness.

Are you traveling with us?

It seems difficult to imagine that our genes can influence something as complex and abstract as aspects of personality and the way in which we experience different emotions. It is important to understand that genes are not determinants, they simply condition, along with environmental factors, the way we think and feel. We invite you to undertake an exciting journey with ADNTRO to discover your genetic personality.

Bibliography

Articles

  • Reza Suárez et al., "The influence of emotions on facial expressions according to Paul Ekman", Magazine Contributions to the Social Sciences, (April-June 2016).
  • Bouchard et al., "Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart", Science, vol 250, 1990, pp. 223-228.
  • Liu et al., "The association between well-being and the COMT gene: Dispositional gratitude and forgiveness as mediators" Journal of Affective Disorders, vol 214, May 2017, Pages 115-121.
  • Okbay et al., ”Genetic variants associated with subjective well-being, depressive symptoms, and neuroticism identified through genome-wide analyzes”. Nature Genetics, vol. 48, 2016, pp. 624-633.
  • McQuaid et al., "Oxytocin and Social Sensitivity: Gene Polymorphisms in Relation to Depressive Symptoms and Suicidal Ideation ”. Frontiers in Human Neuroscience, 2016. doi: 10.3389 / fnhum.2016.00358

Another resources:

  • Carlos López-Otín, “Life in four letters”. Editorial Planeta, 2019.

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