Genomics of personality traits

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Personality traits are patterns of thoughts, feelings and behaviors that reflect the tendency to respond in certain ways under certain circumstances. [1]

Contents

Personality is influenced by genetic and environmental factors and associated with mental health. [2] Beside the environment factor, genetic variants can be detected for personality traits. These traits are polygenic. Significant genetic variants are present for most of the behavioral traits. There is a consistency in detection of genetic variants and genomic association for traits derived from pedigree. [3]

Personality trait research has been conducted both for humans and non-human animals like dogs.

Trait theory

For humans, the Big Five personality traits, also known as the five-factor model (FFM) or the OCEAN model, is the prevailing model for personality traits. When factor analysis (a statistical technique) is applied to personality survey data, some words or questionnaire items used to describe aspects of personality are often applied to the same person. For example, someone described as conscientious is more likely to be described as "always prepared" rather than "messy". This theory uses descriptors of common language and therefore suggests five broad dimensions commonly used to describe the human personality and psyche.

The five factors are:

Methods

The methods mostly used in genomics of personality traits' studies are two: analytic methods and non-analytic ones (such as questionnaires).

Analytic

Analytical techniques that can be used to measure genomics of personality include:

  1. GWAS, genome wide association study is a method used to define markers (these markers are single nucleotide polymorphism, SNPs) across the genomes [3] in order to better understand the contribution of genetics to personality traits. Since SNPs occur in the DNA between genes, GWAS technique aims to find those genes that are associated with certain personality traits, for example neuroticism was reported to be associated with intronic variant in MAGI1 and openness with variants near RASA1. [2] Recently, UK Biobank achieved several SNPs that are associated with neuroticism. The first GWAS studies on all five human personality factors (i.e. neuroticism, extraversion, openness to experience, conscientiousness and agreeableness) used a sample of 3972 individuals from an isolated population on Sardinia, Italy, and found 362 129 SNPs.
  2. DNA genotyping, which can be performed through different kits, for example:
    • The CanineHD BeadChip [3] containing 173,662 validated SNPs derived from the Dog Genome Sequencing Project. This chip has 99.99% of reproducibility, it is a PCR-free protocol, it provides a uniform genome-wide coverage by the 70 markers placed on the platform, it has a high-throughput (up to 12 samples in parallel) and it can be applied to the interrogation of genetic variation in any domestic dog breed. The full set of SNPs that it contains can be analysed with the purpose of explaining the proportion of the phenotypic traits' variances and to show the "genomic heritabilities" of the traits (considering the total of the autosomal and X-linked estimates). For example, the study [3] that used this approach revealed a significant genetic variance present for most of the behavioural traits examined.
    • The Infinium OmniExpress-24 BeadChip array [3] containing 710,000 SNPs.
    • The data obtained from the DNA genotyping can be filtered by many software, such the Genome Studio one, which is able to analyze SNP data across 5 million markers and probes and that can detect sample outliers. Moreover, the data can be then subjected to stringent quality controls, such that of PLINK v1.9.
  3. RNA sequencing can provide a more precise elucidation of common genetic influences on gene expression in the developing brain and the molecular differences that could confer susceptibility to neuropsychiatric disorders. With this technique combined to the GWAS, it was possible, [3] to provide the first eQTL dataset derived exclusively from the human fetal brain. One example of protocol used to do it is the following: [3] total RNA was treated with DNase and purified. Integrity of RNA was assessed and then RNA-Seq libraries were prepared using 1 μg of purified total RNA, depleting ribosomal RNA and modifying the RNA fragmentation times for lower RIN samples (<7). Also library size was assessed and then libraries were quantified. At the end, libraries were sequenced, generating at least 50 million read pairs (100 million reads) per sample.
  4. Whole-Genome Bisulfite Sequencing (WGBS) to examine DNA methylation in cellular subpopulations isolated from human brain tissue. This analysis is important, because DNA methylation differences between neuronal and non-neuronal populations have been widely reported and many neuropsychiatric diseases preferentially affect neuronal subpopulations present in particular brain regions. [4] An example of WGBS protocol is the following: [4] samples were fragmented and then they were bisulfite converted after size selection. Amplification was performed after the bisulfite conversion using Kapa Hifi Uracil + polymerase at the following cycling conditions: 98 °C 45 s/8 cycles: 98 °C 15 s, 65 °C 30 s, 72 °C 30 s/72 °C 1 min. Final libraries were run for quality control purposes. Then, libraries were quantified by qPCR. Libraries were also sequenced using a 125 bp paired-end single indexed run.
  5. Karyotyping is performed to determine fetal sex. Sex is a parameter considered as a covariate in some studies [5] of characterization of personality traits.
  6. Candidate gene approach focus on genes whose function suggests an association with a trait. Originally, it was assumed that few key genes were responsible for the observed heritable variance of personality features. Even though the complexity behind the polygenicity of personality traits was demonstrated, candidate gene studies are still performed today. The small number of genes selected for this type of studies are included in neurotransmission patterns, like the ones involving dopamine and serotonin. The most studied candidate genes and polymorphism related to personality, with the most informative meta-analyses, are DRD4 and 5HTT. DRD4 encodes for the D4 dopamine receptor, while 5HTT encodes for a serotonin transporter responsible for the reuptake of this neurotransmitter. [1] According to some publications, SNPs in DRD4 are associated with extraversion and novelty seeking. [6] Also variations in 5HTT are associated with neuroticism and harm avoidance. [7]
  7. Family and twins studies: The studies of genomics of personality traits involves families and specifically twins, because they have a high heritability of the traits. The families and twins studies have showed that personality traits are moderately heritable, and can predict various lifetime outcomes, including psychopathology. The identical twins have a heritability of 40%, [1] suggesting that the additive genetic effects are responsible for the variance of personality traits for a moderate portion. Family and adoption studies have yielded of approximately 30%. [1] The sex is not involved in heritability of personality traits, on the other end environmental differences can increase or decrease the importance of genetic factors. Twins data shows that genetic influences contribute to personality stability and are relatively constant with age whereas environmental influence on personality increases with age. In addition, twin and family studies show strong genetic correlations across diverse cognitive domains, suggesting pleiotropy, and across levels of ability, substantiating the view of general intelligence as an etiological continuum. [2] The families have members affected by psychiatric disorder, because these diseases can be considered as extremes of normal tendencies and personal traits. It is intended to foster a biological analysis of behavior in order to study neurological disorder and find a correlation with human personality, meaning that heritable variation in personality traits would share a common genetic basis with psychiatric diseases. The geneticists define the phenotype of the patients following the Human Phenotype Ontology (HPO) [8] which provides a standardized vocabulary of phenotypic abnormalities encountered in human disease. The study of complex trait in genetics presents a gap defined as "missing heritability", [9] so a single genetic variations cannot account for much of the heritability of diseases, behaviors, and other phenotypes. For example, a person susceptibility to disease may depend more on the combined effect of all the genes in the background than on the disease genes in the foreground, or the role of genes may have been severely overestimated.

Non analytic

Non-analytic methods mainly use approach is that of questionnaire, here discuss:

Questionnaires:

As previously mentioned, questionnaires were often used as another tool to analyze the association of a behaviour to genetic variances.

In some studies, questionnaires were indirectly given at the owners of the animals involved in the experiment [3] and in other studies they were directly given to the patients involved. [1] [4] These questionnaires were:

  1. C-BARQ, which stands for Canine Behavioural Assessment and Research Questionnaire. It is a survey-based approach used in a large number of studies on dog behaviour, where the dog owner's answers to validated questionnaires to assess the personality traits of the dog. C-BARQ was developed at the University of Pennsylvania and its reliability, validity and standardized test scores support its use as a tool in behavioural researches. The C-BARQ survey contains 101 questions regarding the dog's behavioural response to various situations, with answers marked on a five-step scale. Depending on the results obtained from the compilation of the survey the dogs are divided into 11-14 behavioural traits' groups. [3]
  2. Demographic questionnaires about general information of the dogs, such as sex, neuter status, housing, coat colour, health status, exercise per day and "Role" (based on the activities of the dog). [3] The data obtained from questionnaires can be analysed by the Mixed Linear Model (REML) approach, that provides a consistent and accurate estimation of non-normally-distributed traits. This approach can be implemented using software as ASReml. [3]
  3. Self-report questionnaires, which investigate several aspects of participants' life. Some examples are the following: [1] [4]
    • The Eysenck Personality Questionnaire (EPQ), defines 3 traits of personality: psychoticism (characterized by aggressiveness and interpersonal hostility), extraversion (manifested in outgoing, energetic behaviour) and neuroticism (typified by emotional stability).
    • The Tridimensional Personality Questionnaire (TPQ) defines 3 traits of personality that are based on the biochemical bases of temperament: novelty seeking, harm avoidance and reward dependence.
    • TheTemperament and Character Inventory (TCI) defines 4 personality: persistence (or perseverance despite fatigue or frustration), self-directedness (the ability to modify behaviour in order to achieve personal goals), cooperativeness (the tendency to exhibit agreeable relations with others) and self-transcendence (associated with experiencing spiritual aspects of the self).
    • The Five Factor model (NEO-PI) is based on biological mechanisms shaping 5 higher-order traits (the big five): neuroticism (proneness to experience negative affect), extraversion (motivation to engage with others), openness to experience (inventive or curious behaviour), agreeableness (friendliness and compassion toward others) and conscientiousness (attentive and organized behaviour). This questionnaire is the most commonly used for genetic studies and it has also derivative types, such as the NEO-PI-R and NEO-FFI.
    • UK Biobank self-report questionnaire has several questions related to loneliness and social isolation and it permit to identify cases and controls and then also to compare genetic differences.

Some examples of questions are: 'Do you often feel lonely?', to which individuals answered 'yes' (recorded as cases) or 'no' (controls); other questions are based on the quality of social interactions as: 'How often are you able to confide in someone close to you?' (cases were defined as those who answered 'Never or almost never', controls were defined as those who answered 'Almost daily'). [1]

Correlation with psychiatric disorders

Scientists demonstrated that most of personality traits cluster together and they also cluster with most neuropsychiatric disorders and are therefore related. In research, scientists used linkage disequilibrium regression score to investigate the correlation between personality traits and psychiatric disorder. According to LDSC, there is a positive correlation between major depression disorder and neuroticism and a small correlation between schizophrenia and neuroticism; these correlation have also been confirmed in twins studies. Also, neuroticism and openness show strong genetic correlation. Besides, scientists found that there is a positive correlation between first principal component and all psychiatric disorders, but first principal component showed negative correlation with conscientiousness and agreeableness. [1]

Personality features are highly linked with mental, social and physical outcome. For example, scientists realized that schizophrenia and bipolar disorders cluster with openness. Moreover, they demonstrated that ADHD shows the highest correlation with personality trait especially extraversion. Recently, the negative correlation between neuroticism and loneliness was identified as well as a strong correlation between anxiety and neuroticism. Plus, narcissism, psychopathy and Machiavellianism have association with low agreeableness. In general, neuroticism and other personality traits show negative correlation, while openness, extraversion, agreeableness and conscientiousness shows positive correlation. [2]

Example for the genes that they find to be correlative are:

Within 8p23.1, MTMR9 has intronic variant which has association with extraversion and also with neuroticism shows inverse association. Another one is 12q23.3, WSCD2 which is found for extraversion, by using GWAS, it had been shown that this locus has association with bipolar disorder. In addition, L3MBTL2 is associated with both schizophrenia and neuroticism. [2] Another gene is DRD4 which has association with both ADHD and novelty seeking behavior. [10]

Examples

  1. Genetic basis of Dog Personality Traits: in different genomes of dogs, several SNPs are found close to genes with known neurological or behavioral functions. The TH (tyrosin hydroxylase) gene, whose product is LDOPA, the precursor of the neurotransmitter dopamine, is located 1 Mb from the SNP on CFA18 associated with agitated behaviour. Mutation in this gene cause hyperactivity disorder. The TH gene has been associated with activity, impassivity, and inattention in two dog breeds. The SNP associated with NoiseFear is located 0.27 Mb from CADPS2 on CFA20. CADPS2 is a member of a gene family encoding calcium-binding proteins that regulate the exocytosis of neuropeptide encompassing (dense-core) vesicles from neurons and neuron endocrine cells. The gene and its variants have been associated with autism in humans and noise phobia reported for dogs with this SNPs. [3] Similar SNPs in dogs and in humans are correlated with the same gene which has different outcomes in terms of personality traits.
  2. Intelligence is one of the traits that are affected by genetics. Inherited DNA differences are responsible for substantial individual differences in intelligence test scores the 10% variance in intelligence scores explained by the SNP heritability. [9]
  3. From twins studies it is possible to consider neuroticism as a heritable trait, as shown in a meta-analysis of data from over 29 000 twin pairs, in which they found this correlation in 16 twin pairs, independently from the sex of individuals. [1]

Limitations

See also

Related Research Articles

Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their genetic inheritance (nature) and the environmental conditions of their development (nurture). The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French. The complementary combination of the two concepts is an ancient concept. Nature is what people think of as pre-wiring and is influenced by genetic inheritance and other biological factors. Nurture is generally taken as the influence of external factors after conception e.g. the product of exposure, experience and learning on an individual.

<span class="mw-page-title-main">Heritability</span> Estimation of effect of genetic variation on phenotypic variation of a trait

Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"

Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.

In psychology, trait theory is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of traits, which can be defined as habitual patterns of behavior, thought, and emotion. According to this perspective, traits are aspects of personality that are relatively stable over time, differ across individuals, are relatively consistent over situations, and influence behaviour. Traits are in contrast to states, which are more transitory dispositions.

<span class="mw-page-title-main">Human behaviour genetics</span> Field that examines the role of genetic and environmental influences on human behaviour

Human behaviour genetics is an interdisciplinary subfield of behaviour genetics that studies the role of genetic and environmental influences on human behaviour. Classically, human behavioural geneticists have studied the inheritance of behavioural traits. The field was originally focused on determining the importance of genetic influences on human behaviour. It has evolved to address more complex questions such as: how important are genetic and/or environmental influences on various human behavioural traits; to what extent do the same genetic and/or environmental influences impact the overlap between human behavioural traits; how do genetic and/or environmental influences on behaviour change across development; and what environmental factors moderate the importance of genetic effects on human behaviour. The field is interdisciplinary, and draws from genetics, psychology, and statistics. Most recently, the field has moved into the area of statistical genetics, with many behavioural geneticists also involved in efforts to identify the specific genes involved in human behaviour, and to understand how the effects associated with these genes changes across time, and in conjunction with the environment.

<span class="mw-page-title-main">Big Five personality traits</span> Personality model consisting of five broad dimensions

The Big Five personality traits, sometimes known as "the Five-Factor model of personality", is a grouping of five unique characteristics used to study personality. It has been developed from the 1980s onward in psychological trait theory.

A tag SNP is a representative single nucleotide polymorphism (SNP) in a region of the genome with high linkage disequilibrium that represents a group of SNPs called a haplotype. It is possible to identify genetic variation and association to phenotypes without genotyping every SNP in a chromosomal region. This reduces the expense and time of mapping genome areas associated with disease, since it eliminates the need to study every individual SNP. Tag SNPs are useful in whole-genome SNP association studies in which hundreds of thousands of SNPs across the entire genome are genotyped.

Peter McGuffin is a psychiatrist and geneticist from Belfast, Northern Ireland.

In the study of psychology, neuroticism has been considered a fundamental personality trait. In the Big Five approach to personality trait theory, individuals with high scores for neuroticism are more likely than average to be moody and to experience such feelings as anxiety, worry, fear, anger, frustration, envy, jealousy, pessimism, guilt, depressed mood, and loneliness. Such people are thought to respond worse to stressors and are more likely to interpret ordinary situations, such as minor frustrations, as appearing hopelessly difficult. The responses can include maladaptive behaviors, such as dissociation, procrastination, substance use, etc., which aids in relieving the negative emotions and generating positive ones.

<span class="mw-page-title-main">Genome-wide association study</span> Study of genetic variants in different individuals

In genomics, a genome-wide association study, is an observational study of a genome-wide set of genetic variants in different individuals to see if any variant is associated with a trait. GWA studies typically focus on associations between single-nucleotide polymorphisms (SNPs) and traits like major human diseases, but can equally be applied to any other genetic variants and any other organisms.

In multivariate quantitative genetics, a genetic correlation is the proportion of variance that two traits share due to genetic causes, the correlation between the genetic influences on a trait and the genetic influences on a different trait estimating the degree of pleiotropy or causal overlap. A genetic correlation of 0 implies that the genetic effects on one trait are independent of the other, while a correlation of 1 implies that all of the genetic influences on the two traits are identical. The bivariate genetic correlation can be generalized to inferring genetic latent variable factors across > 2 traits using factor analysis. Genetic correlation models were introduced into behavioral genetics in the 1970s–1980s.

In psychology, novelty seeking (NS) is a personality trait associated with exploratory activity in response to novel stimulation, impulsive decision making, extravagance in approach to reward cues, quick loss of temper, and avoidance of frustration. That is, Novelty seeking refers to the tendency to pursue new experiences with intense emotional sensations. It is a multifaceted behavioral construct that includes thrill seeking, novelty preference, risk taking, harm avoidance, and reward dependence. The novelty-seeking trait is considered a heritable tendency of individuals to take risks for the purpose of achieving stimulation and seeking new environments and situations that make their experiences more intense. This trait has been associated with the level of motive and excitement in response to novelty. Persons with high levels of novelty seeking have been described as more impulsive and disorderly than low novelty seekers and have a higher propensity to get involved in risky activities, such as starting to misuse drugs, engaging in risky sexual activities, and suffering accidental injuries. It is measured in the Tridimensional Personality Questionnaire as well as the later version Temperament and Character Inventory and is considered one of the temperament dimensions of personality. Like the other temperament dimensions, it has been found to be highly heritable. Another related term, Variety seeking or variety-seeking buying behavior describes a consumer's desire to search for alternative products even if she or he is satisfied with a current product. For example, someone may drink tea with lunch one day but choose orange juice the next day specifically to get something different. High NS has been suggested to be related to low dopaminergic activity.

Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences, the field broadly investigates the extent to which genetic and environmental factors influence individual differences, and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.

The missing heritability problem is the fact that single genetic variations cannot account for much of the heritability of diseases, behaviors, and other phenotypes. This is a problem that has significant implications for medicine, since a person's susceptibility to disease may depend more on the combined effect of all the genes in the background than on the disease genes in the foreground, or the role of genes may have been severely overestimated.

The alternative five model of personality is based on the claim that the structure of human personality traits is best explained by five broad factors called impulsive sensation seeking (ImpSS), neuroticism–anxiety (N-Anx), aggression–hostility (Agg-Host), sociability (Sy), and activity (Act). The model was developed by Marvin Zuckerman and colleagues as a rival to the well-known five factor model of personality traits and is based on the assumption that "basic" personality traits are those with a strong biological-evolutionary basis. One of the salient differences between these two models is that the alternative five model lacks any equivalent to the dimension called openness to experience in the five factor model.

The biological basis of personality it is the collection of brain systems and mechanisms that underlie human personality. Human neurobiology, especially as it relates to complex traits and behaviors, is not well understood, but research into the neuroanatomical and functional underpinnings of personality are an active field of research. Animal models of behavior, molecular biology, and brain imaging techniques have provided some insight into human personality, especially trait theories.

Predictive genomics is at the intersection of multiple disciplines: predictive medicine, personal genomics and translational bioinformatics. Specifically, predictive genomics deals with the future phenotypic outcomes via prediction in areas such as complex multifactorial diseases in humans. To date, the success of predictive genomics has been dependent on the genetic framework underlying these applications, typically explored in genome-wide association (GWA) studies. The identification of associated single-nucleotide polymorphisms underpin GWA studies in complex diseases that have ranged from Type 2 Diabetes (T2D), Age-related macular degeneration (AMD) and Crohn's disease.

Genome-wide complex trait analysis (GCTA) Genome-based restricted maximum likelihood (GREML) is a statistical method for heritability estimation in genetics, which quantifies the total additive contribution of a set of genetic variants to a trait. GCTA is typically applied to common single nucleotide polymorphisms (SNPs) on a genotyping array and thus termed "chip" or "SNP" heritability.

In statistical genetics, linkage disequilibrium score regression is a technique that aims to quantify the separate contributions of polygenic effects and various confounding factors, such as population stratification, based on summary statistics from genome-wide association studies (GWASs). The approach involves using regression analysis to examine the relationship between linkage disequilibrium scores and the test statistics of the single-nucleotide polymorphisms (SNPs) from the GWAS. Here, the "linkage disequilibrium score" for a SNP "is the sum of LD r2 measured with all other SNPs".

The GWAS catalog is a free online database that compiles data of genome-wide association studies (GWAS), summarizing unstructured data from different literature sources into accessible high quality data. It was created by the National Human Genome Research Institute (NHGRI) in 2008 and have become a collaborative project between the NHGRI and the European Bioinformatics Institute (EBI) since 2010. As of September 2018, it has included 71,673 SNP–trait associations in 3,567 publications.

References

  1. 1 2 3 4 5 6 7 8 9 Sanchez-Roige S, Gray JC, MacKillop J, Chen CH, Palmer AA (March 2018). "The genetics of human personality". Genes, Brain and Behavior. 17 (3): e12439. doi:10.1111/gbb.12439. PMC   7012279 . PMID   29152902.
  2. 1 2 3 4 5 6 Lo MT, Hinds DA, Tung JY, Franz C, Fan CC, Wang Y, et al. (January 2017). "Genome-wide analyses for personality traits identify six genomic loci and show correlations with psychiatric disorders". Nature Genetics. 49 (1): 152–156. doi:10.1038/ng.3736. PMC   5278898 . PMID   27918536.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 Ilska J, Haskell MJ, Blott SC, Sánchez-Molano E, Polgar Z, Lofgren SE, et al. (June 2017). "Genetic Characterization of Dog Personality Traits". Genetics. 206 (2): 1101–1111. doi:10.1534/genetics.116.192674. PMC   5487251 . PMID   28396505.
  4. 1 2 3 4 Rizzardi LF, Hickey PF, Rodriguez DiBlasi V, Tryggvadóttir R, Callahan CM, Idrizi A, et al. (February 2019). "Neuronal brain-region-specific DNA methylation and chromatin accessibility are associated with neuropsychiatric trait heritability". Nature Neuroscience. 22 (2): 307–316. doi:10.1038/s41593-018-0297-8. PMC   6348048 . PMID   30643296.
  5. ↑ O'Brien HE, Hannon E, Hill MJ, Toste CC, Robertson MJ, Morgan JE, et al. (November 2018). "Expression quantitative trait loci in the developing human brain and their enrichment in neuropsychiatric disorders". Genome Biology. 19 (1): 194. doi: 10.1186/s13059-018-1567-1 . PMC   6231252 . PMID   30419947.
  6. ↑ Benjamin J, Li L, Patterson C, Greenberg BD, Murphy DL, Hamer DH (January 1996). "Population and familial association between the D4 dopamine receptor gene and measures of Novelty Seeking". Nature Genetics. 12 (1): 81–4. doi:10.1038/ng0196-81. PMID   8528258. S2CID   24226671.
  7. ↑ Lesch KP, Bengel D, Heils A, Sabol SZ, Greenberg BD, Petri S, et al. (November 1996). "Association of anxiety-related traits with a polymorphism in the serotonin transporter gene regulatory region". Science. 274 (5292): 1527–31. Bibcode:1996Sci...274.1527L. doi:10.1126/science.274.5292.1527. PMID   8929413. S2CID   35503987.
  8. ↑ Niemi ME (2019-07-19). Common genetic variants contribute to risk of rare severe neurodevelopmental disorders (Thesis thesis). University of Cambridge. doi:10.17863/cam.37830.
  9. 1 2 3 4 Plomin R, von Stumm S (March 2018). "The new genetics of intelligence". Nature Reviews. Genetics. 19 (3): 148–159. doi:10.1038/nrg.2017.104. PMC   5985927 . PMID   29335645.
  10. ↑ van Oers K, Mueller JC (December 2010). "Evolutionary genomics of animal personality". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 365 (1560): 3991–4000. doi:10.1098/rstb.2010.0178. PMC   2992743 . PMID   21078651.
  11. 1 2 Hill WD, Arslan RC, Xia C, Luciano M, Amador C, Navarro P, et al. (December 2018). "Genomic analysis of family data reveals additional genetic effects on intelligence and personality". Molecular Psychiatry. 23 (12): 2347–2362. doi:10.1038/s41380-017-0005-1. PMC   6294741 . PMID   29321673.
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