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Epistatic interactions between oxytocin- and dopamine-related genes and trust
Epistatic interactions between oxytocin- and dopamine-related genes and trust
https://orcid.org/0000-0001-9091-7477
Koyama Yuna Conceptualization Formal analysis Visualization Writing – original draft 1
Nawa Nobutoshi Writing – review & editing 1
Ochi Manami Data curation Writing – review & editing 2 3
Surkan Pamela J. Writing – review & editing 4
https://orcid.org/0000-0002-1074-3954
Fujiwara Takeo Conceptualization Data curation Funding acquisition Project administration Supervision Writing – review & editing 1 2 *
1 Department of Public Health, Tokyo Medical and Dental University (TMDU), Tokyo, Japan
2 Department of Social Medicine, National Center for Child Health and Development, Tokyo, Japan
3 Department of Health and Welfare Services, National Institute of Public Health, Saitama, Japan
4 Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America
Kavushansky Alexandra Editor
Technion Israel Institute of Technology, ISRAEL
Competing Interests: There are no conflicts of interest to declare.

* E-mail: fujiwara.hlth@tmd.ac.jp
19 9 2024
2024
19 9 e030872823 12 2023
29 7 2024
© 2024 Koyama et al
2024
Koyama et al
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Trust is an essential human trait. Although research suggests that the interplay between oxytocinergic and dopaminergic systems affects trust formation, little research has focused on epistatic (i.e., gene by gene) interaction effects of oxytocin- and dopamine-related genes on trust. Using a sample of 348 adults (114 men), we aimed to investigate the associations between genetic variants in oxytocin- and dopamine-related genes and the general, neighborhood, and institutional trust with consideration of sex differences. Three-way interaction between oxytocin-related gene genotypes, dopamine-related genotypes, and sex was found for the oxytocin receptor gene (OXTR)rs1042778 and the Catechol-O-Methyltransferase gene (COMT) rs4680 genotypes (p = 0.02) and for OXTR rs2254298 and the dopamine D2 receptor gene (DRD2) rs1800497 genotypes (p = 0.01). Further sex-stratified analyses revealed that the interaction between OXTR rs1042778 and COMT rs4680 genotypes was associated with neighborhood trust among men (p = 0.0007). Also, the interaction between OXTR rs2254298 and DRD2 rs1800497 genotypes was associated with institutional trust among men (p = 0.005). Post-hoc analyses found that men with OXTR rs1042778 TG/TT and COMT rs4680 GG genotypes reported higher neighborhood trust than those with GG + AG/AA (B = 13.49, SE = 4.68, p = 0.02), TG/TT + AG/AA (B = 23.00, SE = 5.99, p = 0.001), and GG + GG (B = 18.53, SE = 5.25, p = 0.003). Similarly, men with OXTR rs2254298 AG/AA and DRD2 rs1800497 CC genotypes showed higher institutional trust than those with AG/AA + TT/TC (B = 15.67, SE = 5.30, p = 0.02). We could not find any interacting associations among women. While we note that our sample size and candidate gene approach have a potential risk of chance findings, our study provides an important foundation toward further exploration of sex-specific epistatic interaction effects of oxytocin- and dopamine-related genes on trust, indicating the importance of both systems in trust formation.

http://dx.doi.org/10.13039/100007786 National Center for Child Health and Development Research Development Grant for Child Health and Development (24-12) https://orcid.org/0000-0002-1074-3954
Fujiwara Takeo This work was supported by the Research Development Grant for Child Health and Development from the National Center for Child Health and Development (24-12). There was no additional external funding received for this study. Data AvailabilityThe data analysed in the current study is not publicly available since it is the part of a population-based study conducted by the corresponding author. It is available if approved from the ethics committee of the National Centre for Child Health and Development upon reasonable request (phone number: +81-3-3416-0181). The data can not be deposit to somewhere, either public repository, within the manuscript, or as supplemental file because current data contains genetic information, and in combination with other sociodemographic background, individual can be indetify. Based on Japanese law to protect personal information (APPI), it is not possible to depisit the data which can be identify, called sensitive information.
Data Availability

The data analysed in the current study is not publicly available since it is the part of a population-based study conducted by the corresponding author. It is available if approved from the ethics committee of the National Centre for Child Health and Development upon reasonable request (phone number: +81-3-3416-0181). The data can not be deposit to somewhere, either public repository, within the manuscript, or as supplemental file because current data contains genetic information, and in combination with other sociodemographic background, individual can be indetify. Based on Japanese law to protect personal information (APPI), it is not possible to depisit the data which can be identify, called sensitive information.
==== Body
pmcIntroduction

Trust is an essential human trait and is the basis for two distinctive behaviors that are fundamental to society: group-minded conformity and cooperation across broader interdependent networks [1]. Group conformity promotes group cohesion and strengthens punitive responses to social norm violators in the face of external threats [1]. It is rooted in in-group trust that is based on knowledge about a particular object, for example, neighbors (i.e., neighborhood trust) and public or private institutions such as police and media (i.e., institutional trust). Cooperation, on the other hand, provides an opportunity for people to share risks and gain novel benefits, at the cost of possible exploitation of the benefits by free-riders and cheaters [1]. Cooperation necessitates trust across diverse groups even in the absence of prior knowledge about the members of these groups [1,2]. Thus, cooperation is rooted in general trust, the general tendency to rely on others [3,4]. General trust, neighborhood trust, and institutional trust are interrelated [5], and have been shown to be heritable traits [6], suggesting the existence of shared genetic predisposition. However, it is not known which gene or genes are involved in the formation of trust.

Oxytocin, a nine amino-acid neuropeptide synthesized primarily in the hypothalamus, has known as a “social hormone” owing to its involvement in social behaviors such as parenting and mating [7,8], as well as trust [9]. The oxytocin receptor gene (OXTR) and the cluster of differentiation 38 gene (CD38) are two major genes in the oxytocin signaling pathway [10] and have been widely studied for their relationships with social behaviors [11–13]. However, there have been discrepancies reported in the literature to date. For example, in one study OXTR rs53576 A allele carriers showed more social connectedness [14] while in another study A allele carriers exhibited lower empathy [15] and lower levels of optimism and self-esteem [16] and GG genotyped individuals showed higher trust [17]. For CD38, one study reported that CD38 rs3796863 AA/AC genotypes were associated with more altruistic behaviors [18], while another reported no association [19]. Nonetheless, possessing the CD38 rs3796863 C allele has also been associated with more positive social relationships [20]. Another study showed that CD38 rs3796863 CC risk alleles were related to less parental touch and the lower risk allele was associated with longer durations of parent-infant gaze synchrony and greater parental care [21]. One possible explanation for this discrepancy may lie in sex differences and all of these studies stratified by sex or have examined sex interaction effects. While some studies found different associations between genotypes and social behaviors between men and women [14,17,20], others reported no differences between the sexes [15,18,19].

These current contradictory findings could potentially be explained by the dopamine system. Dopamine is one of the abundant neurotransmitters in the brain and plays a critical role in the regulation of movement, memory function, motivation, reinforcement learning, reward, attention, emotion, and cognitive function [22]. Oxytocin and dopamine receptors are co-expressed in regions of the brain related to social functioning, such as the striatum and prefrontal cortex, and are associated with similar social and affiliative behaviors [23,24]. Thus, some posit that the dopamine system modulates the effect of oxytocin on social behaviors by enhancing the hedonic value of social interactions and by adjusting one’s assessment of the risk of engaging in trust behaviors [23]. For example, carrying certain oxytocin (OXT) genotypes was associated with reduced D2/D3 dopamine receptor availability that represents dopamine release in the ventral and dorsal striatum in the face of social cues [25]. Also, intranasal administration of oxytocin regardless of genotype enhanced the activation of the ventral tegmental area, the core region of the mesolimbic dopamine system, in response to social cues, reflecting the salience of social stimuli that predict rewards [26]. These findings suggest a significant interplay between the oxytocinergic and dopaminergic systems in humans. Others have also reported interaction effects of CD38 rs3796863 and the Catechol-O-Methyltransferase gene (COMT) rs4680, genes affecting COMT activity and therefore the degradation of dopamine, on human amygdala activation during social stimuli [27]. However, studies using social behaviors or social cognition as outcomes have been conducted only in rats [28,29]. Therefore, the nature of interactions between oxytocin- and dopamine-related genes on social cognition, especially trust, in humans is not known in a non-experimental context.

Given these findings, the purpose of this study was to examine interactions between genotypes of oxytocin-related genes (OXTR and CD38) and dopamine-related genes (DRD2 and COMT) in relation to the level of trust (i.e., general trust, neighborhood trust, and institutional trust) among community-dwelling adults. Considering the possibility that the social functions of oxytocin [30] and dopamine [31] may differ between women and men as previously reported, the analyses were stratified by sex.

Materials and methods

Participants

Study participants were recruited at the three-month infant health check-up of their child or grandchild, thus including mothers, fathers, and their parents (i.e., the grandparents of the infants). Infants were between 3 and 10 months of age at the time of recruitment, which took place from March 1st, 2013 to March 31st, 2014 at their three-month infant health check-up in Tokyo (an urban area) or Okinawa (a suburban area), Japan. A total of 364 individuals from 115 families participated. After excluding participants whom we could not conduct genetic tests and thus lacked genetic information (n = 16), the analytic sample totaled 348. Two hundred thirty-four participants (67.2%) were women (i.e., mothers/grandmothers) and between 21 and 77 years old (median: 48.5), and 114 participants were men (i.e., fathers/grandfathers) and between 22 and 73 years old (median: 39.0). Approximately one-third of the women had completed junior college or vocational school (35.5%) while 58.8% of the men graduated college or more, which are the most common educational level of females and males respectively. Other demographic data are shown in Table 1. The study was approved by the ethics committee of the National Centre for Child Health and Development (No. 651) and all participants provided written informed consent.

10.1371/journal.pone.0308728.t001 Table 1 Sample characteristics.

 	Women
(n = 234)	Men
(n = 114)	
Age (median, min/max values)	48.5	21.0/77.0	39.0	22.0/73.0	
Prefecture of residence (N, %)					
    Tokyo	108	46.2	58	50.9	
    Okinawa	126	53.8	56	49.1	
Educational attainment (N, %)					
    < High school	66	28.2	28	24.6	
    Some college	83	35.5	18	15.8	
    University/graduate school	80	34.2	67	58.8	
    Missing	5	2.1	1	0.9	
Household income (JPY) (N, %)					
    < 4 million	85	36.3	33	28.9	
    4–8 million	74	31.6	44	38.6	
    8 million +	48	20.5	33	28.9	
    Missing	27	11.5	4	3.5	
General trust (mean, SD)	63.3	21.3	62.9	21.8	
Neighborhood trust (mean, SD)	59.1	21.2	56.0	22.2	
Institutional trust (mean, SD)	68.2	17.6	61.7	19.7	
Abbreviations: JPY, Japanese yen.

Genotyping

Deoxyribonucleic acid (DNA) was extracted from 2 ml of passive drool saliva samples collected at the study site using the Oragnere® saliva sampling kit (DNA Genotek Inc., Ottawa, Canada), which can keep DNA at room temperature. Genotyping of the gene variants of interest (OXTR rs53576 (within intron 3 of OXTR), rs2254298 (within intron 3 of OXTR), rs1042778 (within the 3’-untranslated region (3’ UTR) of OXTR), CD38 rs3796863 (within intron 7 on chromosome 4p15), COMT rs4680 (within chromosome 22q11.21,16), and DRD2 rs1800497 (within exon 8 of the ankyrin repeat domain, which is one gene downstream of DRD2)) was performed with the TaqMan™ allele-specific amplification method (Life Technologies, Carlsbad, CA), as previously described [32]. The above-mentioned genes were chosen considering the previously reported association with social functioning. OXTR rs53576 genotypes were previously identified as predictors of social connectedness [14] and trust [17]. OXTR rs2254298 was associated with social cognition [33]. OXTR rs1042778 was associated with sociality [34]. CD38 rs3796863 was associated with communal behaviors [20]. COMT rs4680 and DRD2 rs1800497 were chosen since COMT and DRD2 were shown to have interacted with the oxytocin system in social functions [27,29]. All genotype frequencies were confirmed to be in Hardy-Weinberg equilibrium (S1 Table). The population was divided into four groups according to the genotypes of single nucleotide polymorphisms (SNPs) in genes related to the oxytocin (OXTR and CD38) and dopamine (COMT and DRD2) systems. According to a power calculation with the “pwr” package in R [35], 36 to 46 participants in each group were needed to detect a medium to large effect size (f2 = 0.12 to 0.16) with 80% power for an F-test with 4 groups, at the significant level set to 0.001 (= 0.05/ 8 gene combinations, 3 trust types, 2 sex; based on the Bonferroni correction). In order to keep the sample size comparable for each genotype, the sample was divided into 1) a group consisting of homozygotes for the minor allele and heterozygotes for the minor and major alleles, and 2) another group consisting only of homozygotes for the major allele. Since SNP data for OXTR rs2254298 and CD38 rs3796863 were not available from 2 and 3 participants, respectively, sample sizes vary for each analysis on these SNPs.

Trust

Participant trust (i.e., general, neighborhood, and institutional trust) was assessed based on a self-reported questionnaire. Questionnaires were mailed to participants prior to the visit and completed questionnaires were collected at the study site. Participants responded to 10 trust-related questions, reflecting the level of trust in others in general, in their neighbors, and in government agencies. Scale items were developed based on validated scales for measuring trust [36,37]. All items for each dimension of trust are presented in S2 Table. The score for each item was normalized to 0–1 and summed to obtain general, neighborhood, and institutional trust scores (Cronbach’s alpha, general: 0.70; neighborhood: 0.82; institutional: 0.84), which were further normalized to 0–100. The correlations among each dimension of trust were as follows: general and neighborhood trust: 0.45; general and institutional trust: 0.38; neighborhood and institutional trust: 0.32 (all p-values < 0.05). Higher scores indicate higher levels of trust.

Statistical analysis

In order to detect the epistatic interaction effects, we applied multivariate linear regression with an interaction term between oxytocinergic and dopaminergic genes, as well as the interaction with sex. The analysis was conducted for men and women, separately where the significant three-way interaction existed. Additionally, an analysis of variance (ANOVA) was performed to examine the mean differences in trust scores across groups characterized by each genotype. ANOVA was followed by Tukey’s multiple comparison post hoc tests to identify groups with significantly different levels of trust with the R package “multcomp” [38]. To take into account clustering at the family level and age differences, the sandwich variance estimator was applied, and age was adjusted for all models. All analyses were conducted using R version 4.0.5 [39].

Results

Interactions between oxytocin- and dopamine-related gene genotypes were explored (S3 Table). We could not find any significant interaction in the general population. However, the interaction between OXTR rs1042778, COMT rs4680, and sex on neighborhood trust (unstandardized coefficient (B) = 26.38, t = 2.40, p = 0.02), and between OXTR rs2254298, DRD2 rs1800497, and sex on institutional trust (B = -21.04, t = -2.54, p = 0.01) were found. Therefore, we further examined these genotypes by sex.

We found an interaction between OXTR rs1042778 and COMT rs4680 on neighborhood trust scores among men (B = 28.05, t = 3.38, p = 0.0007), but not among women (B = 1.42, t = 0.18, p = 0.86; Table 2). Men with OXTR rs1042778 TG/TT and COMT rs4680 GG genotypes showed higher neighborhood trust compared to any other genotyped groups (vs GG + AG/AA: mean difference ± SE = 13.49 ± 4.68, t = 2.88, p = 0.02; vs TG/TT + AG/AA: mean difference ± SE = 23.00 ± 5.99, t = 3.84, p = 0.001; vs GG + GG: mean difference ± SE = 18.53 ± 5.25, t = 3.53, p = 0.003; Fig 1A and S4 Table).

10.1371/journal.pone.0308728.g001 Fig 1 Mean and distribution of trust scores across genotyped groups among males.

A) Neighbourhood trust scores across male groups genotyped by OXTR rs1042778 and COMT rs4680. B) Institutional trust scores across males genotyped by OXTR rs2254298 and DRD2 rs1800497. Orange and black dots represent individual and mean scores, respectively. Error bars denote standard errors estimated with a sandwich variance estimator. * and ** correspond to a p-value < 0.05 and < 0.01, respectively (adjusted with Tukey’s method).

10.1371/journal.pone.0308728.t002 Table 2 Epistatic interaction effects between OXTR rs1042778 and COMT rs4680 on neighbourhood trust by sex.

 	Female	Male	
 	B	P-value	B	P-value	
OXTR rs1042778 (TG/TT, ref: GG)	0.21	0.97	-9.52	0.10	
COMT rs4680 (GG, ref: TG/TT)	1.09	0.72	-5.04	0.31	
OXTR rs1042778 × COMT rs4680	1.42	0.86	28.05	0.0007	
Bold signifies p < 0.05.

All models were adjusted for age.

Standard errors were calculated with a sandwich variance estimator. B stands for unstandardized coefficient.

An interaction between OXTR rs2254298 and DRD2 rs1800497 genotypes was found among men (B = -19.46, t = -2.82, p = 0.005), but not among women (B = -0.08, t = -0.02, p = 0.99; Table 3). Men with OXTR rs2254298 AG/AA and DRD2 rs1800497 CC genotype showed higher institutional trust than those with OXTR rs2254298 AG/AA and DRD2 rs1800497 TT/TC (mean difference ± SE = 15.67 ± 5.30, t = 2.96, p = 0.02; Fig 1B and S4 Table).

10.1371/journal.pone.0308728.t003 Table 3 Epistatic interaction effects between OXTR rs2254298 and DRD2 rs1800497 on institutional trust by sex.

 	Female	Male	
 	B	P-value	B	P-value	
OXTR rs2254298 (GG, ref: AG/AA)	2.78	0.37	11.66	0.01	
DRD2 rs1800497 (GG, ref: AG/AA)	-3.43	0.25	15.67	0.004	
OXTR rs2254298 × DRD2 rs1800497	-0.08	0.99	-19.46	0.005	
Bold signifies p < 0.05.

All models were adjusted for age.

Standard errors were calculated with a sandwich variance estimator. B stands for unstandardized coefficient.

Discussion

In this study, we observed interactions between OXTR rs1042778 and COMT rs4680 related to neighborhood trust, and between OXTR rs2254298 and DRD2 rs1800497 related to institutional trust in men, but not in women. To the best of our knowledge, this is the first study to examine the gene-by-gene interaction of oxytocin- and dopamine-related genes on different levels of trust among humans in a non-experimental setting, with consideration of potential sex differences and variations regarding the type of trust.

COMT is an enzyme responsible for the methylation of dopamine and regulates dopamine degradation [19,27]. COMT rs4680 polymorphisms are associated with enzyme activity, and A allele carriers have demonstrated reduced enzyme activity, leading to reductions in the degradation of dopamine [19,27]. Reductions in dopamine degradation further indicate higher synaptic dopamine availability [19,27], suggestive of higher dopaminergic functioning. In the present study, we found evidence of an interaction between OXTR rs1042778 and COMT rs4680 on neighborhood trust in men. OXTR rs1042778 TG/TT and COMT rs4680 GG genotypes were associated with the highest level of neighborhood trust compared to their counterparts. The OXTR rs1042778 T allele has been associated with poor sociability [40,41], suggestive of lower levels of trust, albeit without a clear biological role of the polymorphism. Therefore, we had expected that OXTR rs1042778 TG/TT genotype carriers would show lower levels of trust, which was not the case in our analysis. Previously reported associations between the OXTR rs1042778 T allele with anti-social and aggressive behaviors [42], and lower sociability concerning the general population [34,40,43] might be explained by T allele carriers’ higher sensitivity to social stimuli, which was indicated by heightened amygdala reactivity to angry facial expressions [42]. The association between OXTR and social attention was also shown in an animal experiment [44], suggesting this as a well-conserved social response across species. Given that we assessed neighborhood trust (i.e., trust toward well-known people), and that the T allele may be linked to higher sensitivity to social environmental stimuli, it is plausible that the association between the T allele and higher neighborhood trust would be observed in Japan, where the degree of social conformity is relatively high [45]. Our results extended the current literature by suggesting that the OXTR rs1042778 polymorphism alters levels of trust when combined with GG on COMT rs4680, i.e., when dopamine functioning is normal compared with heightened.

DRD2 encodes the D2 subtype of the dopamine receptor (DRD2). DRD2 rs1800497, the most extensively studied polymorphism, can be a marker of the number of dopamine receptors in the striatum [46,47]. Specifically, the T allele is associated with a decrease in the number of DRD2 [46,47], and thus a decreased level of dopamine functioning. The current study revealed that men with OXTR rs2254298 AG/AA and DRD2 rs1800497 TT/TC showed lower institutional trust than men with OXTR rs225498 AG/AA and DRD2 rs1800497 CC. Similar to the OXTR rs1042778 T allele, the OXTR rs2254298 G allele has been tied with poor sociability and, thus lower levels of trust [40,41]. Therefore, OXTR rs2254298 AG/AA genotypes would indicate higher levels of trust. Our findings showed social functions of OXTR rs2254298 A allele might be stronger in the absence of strong dopamine functions, i.e., with DRD2 rs1800497 TT/TC genotypes.

Several prior studies have reported oxytocin-dopamine interactions on emotional responses in individuals. A study of European young men showed that men with CD38 rs3796863 CC (previously identified as a risk genotype) and COMT rs4680 AA, and men with CD38 rs3796863 AA/AC and COMT rs4680 GG showed stronger activation of the amygdala, which governs the emotional process, during the presentation of social stimuli than their counterparts carrying CD38 rs3796863 AA/AC and COMT rs4680 AA, and CD38 rs3796863 CC and COMT rs4680 GG, respectively [27]. Another study found that participants with more striatal dopamine transporter availability were more prone to neuroticism only among OXTR rs53576 AA carriers [48]. We did not observe exactly the same association. However, the association between risk alleles on oxytocin-related genes and poor social functioning in people with low to standard levels of dopamine functioning is consistent with our findings. Furthermore, this association was attenuated, albeit not reversed in our study sample, among people with high dopamine functioning levels.

These findings on the interaction between oxytocin- and dopamine-related gene genotypes suggest that oxytocin-related genes determine the basis of trust in an individual by altering one’s tendency for social affiliation and the ability to process social information [10]. One’s ability to social process can be modified by a propensity to engage in risk-taking behaviors [2], which may be facilitated by levels of dopamine functioning. Some of the social functions governed by dopamine are attributable to reward-prediction errors that bias behavioral selection toward stimuli that predict a reward [49]. Thus, lower levels of dopamine functioning may strengthen the association between the oxytocin risk allele and lower levels of trust since people with lower levels of dopamine functioning tend not to take risks and do not view social interactions as rewarding. In contrast, higher levels of dopamine functioning may weaken the association between the oxytocin risk allele and lower levels of trust because people with higher levels of dopamine functioning tend to take risks and trust people in general (as they are motivated by their ability to get more rewards from social interactions).

Prior research suggests that oxytocin [30] and dopamine [31] have sex-specific associations with social behaviors, which may explain the differential associations by sex we observed in the current study. In particular, it has been hypothesized that there is an inverted U-shaped association between brain oxytocin level and social functions that explains sex differences in sensitivity to oxytocin administration, i.e. suggesting that females can enhance social behaviors more sensitively with oxytocin administration, while males require higher doses of oxytocin to change their behaviors [30,50]. Considering sex differences in social functioning from an evolutionary viewpoint, this sex difference in sensitivity seems reasonable, as females are more empathic and sensitive to social signals and choose fewer close social relationships, whereas males prefer aggressive behavior, risk-taking, and more extensive but less intimate relationships [51]. The current focus is on gene variants related to oxytocin and dopamine systems that do not necessarily correspond to the level of exogenously administered and centrally available oxytocin and dopamine and their levels of functioning. Therefore, an alternative explanation would be that existing sex differences in signaling and neural pathways could modify social behaviors. The current study did not uncover any sex-specific mechanisms and we cannot rule out the possibility of chance findings due to the small sample size in each group. Therefore, replication studies with larger sample sizes to examine potential sex differences are needed.

We must be aware of some limitations. First, general trust was assessed with two questions. Although these items were based on prior research [36,37], they may not perfectly capture the concept of general trust with only two items. Further, assessing the act of trust in experimental settings, such as the Trust Game, should be considered [37]. Second, we could not examine the possible epistatic interaction effects on DNA methylation [52], and other epistatic interactions that were not assessed here (e.g., between COMT and DRD2 on emotionality [53]). Thus, future replication studies were warranted. Third, our study sample was exclusively Japanese. Generalizing the current findings needs caution with the consideration of cultural differences in trust and ethnic variations in genes. Fourth, we interpreted gene variants as estimated dopamine levels, i.e., there may be a discrepancy between our estimates of dopamine function deduced from genotypes versus the assessment of actual dopamine levels. However, considering the challenges of measuring dopamine levels in the living human brain, the use of gene variants may be advantageous because they are not subject to fluctuations due to biological responses to internal and external environmental changes (i.e., negative and positive feedback) and allow us to exclude reverse causation (e.g., that higher levels of trust lead to more social interactions, which result in higher peripheral oxytocin levels [54]). The use of human samples is another strength of our research considering that trust in humans and other animals has potentially different meanings and the neural system processes them differently.

Conclusions

Our study found an interaction between OXTR rs1042778 and COMT rs4680 on the level of neighborhood trust and an interaction between OXTR rs2254298 and DRD2 rs1800497 on institutional trust among men. Although we need caution in the interpretation due to the small sample size, our results provided preliminary findings that set the stage to further explore the epistatic interactions between oxytocin- and dopamine-related gene variants on social phenotypes, such as trust, by underscoring the importance of the dopamine system as well as the oxytocin system in the formation of trust. Given the growing significance of understanding how trust influences multidimensional human activities, further research is needed to fully elucidate the mechanisms of trust formation in humans.

Supporting information

S1 Table Frequency and distribution of genotypes of oxytocin- and dopamine-related genes.

(DOCX)

S2 Table Trust questionnaire items.

(DOCX)

S3 Table Epistatic interaction effects between oxytocin- and dopamine-related genotypes on trust.

(DOCX)

S4 Table Trust mean score by genotyped groups.

(DOCX)

We thank all study participants and their family members who took part in this study.

10.1371/journal.pone.0308728.r001
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Kavushansky Alexandra Academic Editor
© 2024 Alexandra Kavushansky
2024
Alexandra Kavushansky
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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PONE-D-23-41164Epistatic interactions between oxytocin- and dopamine-related genes and trustPLOS ONE

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Reviewer #1: No

Reviewer #2: Partly

Reviewer #3: No

**********

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Reviewer #1: I Don't Know

Reviewer #2: No

Reviewer #3: Yes

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

**********

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**********

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Reviewer #1: Please see the attached file.

Reviewer #2: Overall a nice paper but some clarification needed in places. Supp tables are overviews rather than data so this may needed added in to satisfy point 3 about data underlying findings.

Line 23: OXTR and COMT not defined in abstract

Line 24: DRD4 not defined in abstract

Line 46: Citation for sentence ending “… free-riders and cheaters”.

Line 54: CD not defined

Line 63: consider adding “as” to make clearer. “… sex differences as all of these studies….”

Line 80: COMT not defined

Line 82: clarification of use of word “endpoints”

Line 95: confusing first line of method. Once whole section is read meaning is clear, but it adds confusion with the first line wording as is. Perhaps “Study participants were recruited at the three-month infant health check-up of their child or grandchild”.

Line 99: is it standard for genetic information to be known about citizens in Japan? Maybe add a sentence here as this is unusual in other parts of the world.

Lines 100-102: add mean age of participants with the range

Line 102 – 103: for females junior college and vocational reported and for males graduated college reported. Consider reporting same education level for M&F e.g. how many females graduated college so that it is comparable. Or emphasises that these were the most common categories for both sexes.

Line 109: How were the saliva samples treated and stored?

Line 110: specify the type of variant (SNPs but also what type e.g. upstream, 5’ UTR etc).

Line 112: were PCR protocols optimised or were they identical to reference 30? Gel % and stain type, primers all the same?

Line 144: stats – was relatedness between individuals accounted for? i.e. if there was a mother and grandmother that were themselves mother and daughter. If participants were not related specify this in participant info section. If individuals were related, consider a MCMC-based Bayesian GLMM with priors to reduce chance of type 1 errors. If this stats test is not possible comment on how relatedness was accounted for in the analysis.

Line 145: unclear why multivariate linear regression was used in addition to ANOVA when the variables used were categorical (genes and sex) and therefore more suited to the ANOVA. If these are not categorical perhaps a data prep section would help with clarification here.

Line 151: reference needed for package

Line 158-159: no test statistic or dfs reported with results.

Line 162: which test does the B value come from. As far as I am aware you get t from LR and f from ANOVA. If another test was conducted this needs reported in the stats section. If B is something other than the test statistic this needs explained here. Same in Tables 2 and 3.

Line 162: Consider “…among women (B=1.42, p = 0.86; Table 2).” Rather than having brackets back to back. Same on line 166 and 172.

Line 164-165: report df for genotypes and for M&F for the genotypes on line 169-172.

Line 190 (OXTR discussion): consider also OXTR has been shown to be linked with social attention in rhesus macaques (Howarth et al., 2023; 10.1371/journal.pone.0288108) suggesting that this is a well conserved social response across species.

Line 219: A allele carries for OXTR rs53576 were also had lower level of optimism and self-esteem (Saphire-Bernstein et al., 2011; https://doi.org/10.1073/pnas.1113137108) and have poor social recognition (Skuse et al., 2014; 10.1073/pnas.1302985111).

Line 255: how might they not capture the concept of general trust?

Line 265: why is using humans a strength?

Figure 1 is blurry but downloadable version is fine

Reviewer #3: The study used a candidate gene family study approach to select variants in biological systems that have been strongly implicated in trust and test for an epistatic interaction to understand genetic contributions to self-report trust measures, stratified by sex. The justification for the biological systems selected is sound and well-explained. However, unfortunately the changing conventions and standards of evidence in the field of behavior genetics draw immediate concerns about the strength of this study.

Candidate gene association studies have received intense scrutiny for issues with replication, with genetics journals resistant to publishing these types of studies at all for the past dozen years (Hewitt, 2012). More recent meta-analytic evidence revisiting the topic of candidate gene approaches vs. genome wide association study (GWAS) also urges researchers to discontinue the use of candidate gene approaches (van de Weijer, 2022). For even longer, the best practice standard for candidate gene studies has insisted on sample sizes of at least 1,000 participants (Duncan & Keller, 2011). Although family studies with a candidate gene approach may have value, current scientific attitudes advocating for these types of approach say that sample sizes in the thousands are expected, and the evidence is more valuable if not relying solely on a candidate gene approach but instead working in concert with GWAS evidence (Friedman, et al., 2021).

Due to the interaction terms in this study and running analyses separately by gender, the already small sample size of 364 individuals has further reduced statistical power, leading to concern that the significant findings are false positives, as appears to be the case for most findings from studies of these types based on failures to replicate (Border et al., 2019, Hatoum et al., 2020; Johnson, et al., 2017; Farrell et al., 2015; Culverhouse, et al., 2018; Duncan & Keller, 2011; Duncan et al., 2019).

Based on the fundamental failure of this study to meet the current standards of behavior genetics research, I unfortunately cannot recommend publication. For serious consideration of this evidence, I would need to at least see an independent replication with a sample size in the thousands, but most geneticists would still be hesitant to give this evidence much confidence without supporting GWAS evidence. I would recommend the authors read the paper by Friedman et al., 2021 (https://doi.org/10.1016/j.tics.2021.06.007), if they have not already, and consider revising their approach to these research questions. I wish the researchers the best luck; conducting research in such a rapidly changing field undergoing major paradigm shifts is challenging but based on the researchers’ clear expertise in the biological systems of interest, I am confident they will produce other valuable work in the future.

**********

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Reviewer #2: Yes: Emmeline Howarth

Reviewer #3: No

**********

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Attachment Submitted filename: PLOS (1).pdf

10.1371/journal.pone.0308728.r002
Author response to Decision Letter 0
Submission Version1
25 Jun 2024

Rebuttal letter

Reviewer #1

The manuscript by Koyama et al. attempts to establish a link between the oxytocinergic and dopaminergic systems, hypothesizing an epistatic relationship between the corresponding genes. These gene sets play key roles in shaping behaviours of key societal significance. The study’s findings highlight the presence of an interaction between OXTRrs1042778 and COMTrs4680 concerning neighbourhood trust. An interaction was also observed between OXTRrs2254298 and DRD2rs1800497 impacting institutional trust, but exclusively among males. While these results, albeit limited, may be of interest to a specialized audience, the manuscript is not without its limitations.

Response:

Thank you so much for acknowledging the potential interests of our findings. We tried to address the points you raised in the following manners.

#1. Firstly, the authors devote scant attention to the literature on CD38 and its role in confidence, a subject extensively discussed by biologists and medical groups working in different fields. Moreover, references to most of the pivotal papers on the subject are conspicuously absent.

Response:

Thank you for your point. We searched the literature again to cover the crucial articles about CD38 and social relationships in the introduction.

“Another study showed that CD38 rs3796863 CC risk alleles were related to less parental touch and the lower risk allele was associated with longer durations of parent-infant gaze synchrony and greater parental care [21].” (Introduction: paragraph 2)

#2. Another limitation is the failure to analyse the results in relation to the sex of the subjects.

Response:

Thank you for pointing out the limitation. We conducted formal statistical tests of effect modification by sex (inclusion of interaction terms by sex) and stratified analyses where the interaction was significant with the potential sex differences in mind. However, as stated in the discussion, we could not exclude the potential chance findings due to the small sample size. Given this limitation, we toned down our discussion regarding the sex differences in the conclusion and abstract.

“Although we need caution in the interpretation due to the small sample size, our results provided preliminary findings that set the stage to further explore the epistatic interactions between oxytocin- and dopamine-related gene variants on social phenotypes, such as trust, by underscoring the importance of the dopamine system as well as the oxytocin system in the formation of trust.” (Conclusions)

“While we note that our sample size and candidate gene approach have a potential risk of chance findings, our study provides an important foundation toward further exploration of sex-specific epistatic interaction effects of oxytocin- and dopamine-related genes on trust, indicating the importance of both systems in trust formation.” (Abstract)

#3. A second, and arguably more critical limitation, is the exclusive focus on Japanese individuals in the analysis. While this is not problematic per se and may contribute valuable insights within the context of Japan, it makes the conclusions difficult to extrapolate to societies lacking the peculiar characteristics of Japanese society. These factors hinder the extension of the study’s results to a broader audience. The authors acknowledge additional limitations at the conclusion of an extensive discussion.

Response:

Thank you for raising the important limitation in the current study. Since trust is one of the phenotypes that is strongly affected by social contexts and genes are heavily rooted in ethnic differences, we further acknowledged and added this limitation regarding the generalizability to the discussion.

“Third, our study sample was exclusively Japanese. Generalizing the current findings needs caution with the consideration of cultural differences in trust and ethnic variations in genes.” (Discussion: paragraph 7)

Reviewer #2:

#1. Overall a nice paper but some clarification needed in places. Supp tables are overviews rather than data so this may needed added in to satisfy point 3 about data underlying findings.

Response:

Thank you for your kind compliments on our overall manuscript. We revised the manuscript regarding your points as follows.

#2. Line 23: OXTR and COMT not defined in abstract

#3. Line 24: DRD4 not defined in abstract

Response:

Thank you for your point. We added the full names for the first abbreviations in the abstract.

“Three-way interaction between oxytocin-related gene genotypes, dopamine-related genotypes, and sex was found for the oxytocin receptor gene (OXTR)rs1042778 and the Catechol-O-Methyltransferase gene (COMT) rs4680 genotypes (p = 0.02) and for OXTR rs2254298 and the dopamine D2 receptor gene (DRD2) rs1800497 genotypes (p = 0.01).” (Abstract)

#4. Line 46: Citation for sentence ending “… free-riders and cheaters”.

Response:

We added the reference for that sentence.

“Cooperation, on the other hand, provides an opportunity for people to share risks and gain novel benefits, at the cost of possible exploitation of the benefits by free-riders and cheaters [1].” (Introduction: paragraph 1)

#5. Line 54: CD not defined

Response:

We added the full name for CD38.

“The oxytocin receptor gene (OXTR) and the cluster of differentiation 38 gene (CD38) are two major genes in the oxytocin signaling pathway [10] and have been widely studied for their relationships with social behaviors [11–13].” (Introduction: paragraph 2)

#6. Line 63: consider adding “as” to make clearer. “… sex differences as all of these studies….”

Response:

Thank you for your suggestion. We connected two sentences so that our implied contents would be better conveyed.

“One possible explanation for this discrepancy may lie in sex differences and all of these studies stratified by sex or have examined sex interaction effects.” (Introduction: paragraph 2)

#7. Line 80: COMT not defined

Response:

We added the full name for the abbreviation.

“Others have also reported interaction effects of CD38 rs3796863 and the Catechol-O-Methyltransferase gene (COMT) rs4680, genes affecting COMT activity and therefore the degradation of dopamine, on human amygdala activation during social stimuli [27].” (Introduction: paragraph 3)

#8. Line 82: clarification of use of word “endpoints”

Response:

In order to clarify the meaning of a sentence, we changed the word from “endpoints” to “outcomes”.

“However, studies using social behaviors or social cognition as outcomes have been conducted only in rats [28,29].” (Introduction: paragraph 3)

#9. Line 95: confusing first line of method. Once whole section is read meaning is clear, but it adds confusion with the first line wording as is. Perhaps “Study participants were recruited at the three-month infant health check-up of their child or grandchild”.

Response:

Thank you for your suggestion and for pointing out the potential confusion. We followed your suggestion and clarified the recruiting process.

“Study participants were recruited at the three-month infant health check-up of their child or grandchild, thus included mothers, fathers, and their parents (i.e., the grandparents of the infants).” (Materials and methods: Participants)

#10. Line 99: is it standard for genetic information to be known about citizens in Japan? Maybe add a sentence here as this is unusual in other parts of the world.

Response:

Thank you for pointing out the potential unclear sentence. It is not standard for Japanese citizens to know genetic information. The genetic information was obtained exclusively among the study participants by our team. We made this point clearer.

“After excluding participants whom we could not conduct genetic tests and thus lacked genetic information (n = 16), the analytic sample totaled 348.” (Materials and methods: Participants)

#11. Lines 100-102: add mean age of participants with the range

Response:

We added the median age of participants in addition to the range of ages with the consideration of skewed distributions.

“Two hundred thirty-four participants (67.2%) were women (i.e., mothers/grandmothers) and between 21 and 77 years old (median: 48.5), and 114 participants were men (i.e., fathers/grandfathers) and between 22 and 73 years old (median: 39.0).” (Materials and methods: Participants)

#12. Line 102 – 103: for females junior college and vocational reported and for males graduated college reported. Consider reporting same education level for M&F e.g. how many females graduated college so that it is comparable. Or emphasises that these were the most common categories for both sexes.

Response:

We picked up these categories since they are the most common educational level categories of females and males. We made emphasis on this point.

“Approximately one-third of the women had completed junior college or vocational school (35.5%) while 58.8 % of the men graduated college or more, which are the most common educational level of females and males respectively.” (Materials and methods: Participants)

#13. Line 109: How were the saliva samples treated and stored?

Response:

Saliva samples kept in a saliva sampling kit were stored at room temperature. This is described in Method as follows:

“Deoxyribonucleic acid (DNA) was extracted from 2 ml of passive drool saliva samples collected at the study site using the Oragnere® saliva sampling kit (DNA Genotek Inc., Ottawa, Canada), which can keep DNA at room temperature.” (Materials and methods: Genotyping)

#14. Line 110: specify the type of variant (SNPs but also what type e.g. upstream, 5’ UTR etc).

Response:

We added the explanation of location to the SNPs.

“Genotyping of the gene variants of interest (OXTR rs53576 (within intron 3 of OXTR), rs2254298 (within intron 3 of OXTR), rs1042778 (within the 3’-untranslated region (3’ UTR) of OXTR), CD38 rs3796863 (within intron 7 on chromosome 4p15), COMT rs4680 (within chromosome 22q11.21,16), and DRD2 rs1800497 (within exon 8 of the ankyrin repeat domain, which is one gene downstream of DRD2)) was performed with the TaqMan™ allele-specific amplification method (Life Technologies, Carlsbad, CA), as previously described [32].” (Materials and methods: Genotyping)

#15. Line 112: were PCR protocols optimised or were they identical to reference 30? Gel % and stain type, primers all the same?

Response:

Reference 30 analyzed the same sample of our study. Therefore, the PCR protocols are identical to that of reference 30. (now updated as reference 32)

#16. Line 144: stats – was relatedness between individuals accounted for? i.e. if there was a mother and grandmother that were themselves mother and daughter. If participants were not related specify this in participant info section. If individuals were related, consider a MCMC-based Bayesian GLMM with priors to reduce chance of type 1 errors. If this stats test is not possible comment on how relatedness was accounted for in the analysis.

Response:

Thank you for pointing out the important statistical considerations and further suggestions. We took into account the sample clustering within families by estimating standard error using a robust variance estimator as stated in the statistical analysis section.

“To take into account clustering at the family level and age differences, the sandwich variance estimator was applied, and age was adjusted for all models.” (Materials and methods: Statistical analysis)

#17. Line 145: unclear why multivariate linear regression was used in addition to ANOVA when the variables used were categorical (genes and sex) and therefore more suited to the ANOVA. If these are not categorical perhaps a data prep section would help with clarification here.

Response:

First, essentially, we note that linear regression and ANOVA do the same mathematical calculations and have no superiority to each other. We mentioned our statistical procedure as multivariate linear regression simply because we run with the R function “lm”, which provides the same results as the R function “aov”, a function designed solely for ANOVA. Second, we preferred linear regression outputs here since this provided a difference score, which notified the readers of the strength of impact given the trust score range. This was followed up with a graphical description, giving the information about scores of each group.

#18. Line 151: reference needed for package

Response:

We added the citations where applicable.

“According to a power calculation with the “pwr” package in R [35],36 to 46 participants in each group were needed to detect a medium to large effect size (f2 = 0.12 to 0.16) with 80% power for an F-test with 4 groups, at the significant level set to 0.001 (= 0.05/ 8 gene combinations, 3 trust types, 2 sex; based on the Bonferroni correction).” (Materials and methods: Genotyping)

“ANOVA was followed by Tukey’s multiple comparison post hoc tests to identify groups with significantly different levels of trust with the R package “multcomp” [38].” (Materials and methods: Statistical analysis)

33. Champely S. pwr: Basic Functions for Power Analysis. 2020. Available: https://CRAN.R-project.org/package=pwr

36. Westfall THFB. Simultaneous Inference in General Parametric Models. Biometrical Journal. 2008;50: 3446–3363.

#19. Line 158-159: no test statistic or dfs reported with results.

Response:

I added the effect size and t-statistics in addition to the p-values in the result.

“However, the interaction between OXTR rs1042778, COMT rs4680, and sex on neighborhood trust (unstandardized coefficient (B) = 26.38, t = 2.40, p = 0.02), and between OXTR rs2254298, DRD2 rs1800497, and sex on institutional trust (B = -21.04, t = -2.54, p = 0.01) were found.” (Results: paragraph 1)

#20. Line 162: which test does the B value come from. As far as I am aware you get t from LR and f from ANOVA. If another test was conducted this needs reported in the stats section. If B is something other than the test statistic this needs explained here. Same in Tables 2 and 3.

Response:

B corresponds to the unstandardized effect size in the linear regression. I made a note for the first appearing B in the text and put a footnote to the table to explain what B stands for.

“However, the interaction between OXTR rs1042778, COMT rs4680, and sex on neighborhood trust (unstandardized coefficient (B) = 26.38, t = 2.40, p = 0.02), and between OXTR rs2254298, DRD2 rs1800497, and sex on institutional trust (B = -21.04, t = -2.54, p = 0.01) were found.” (Results: paragraph 1)

#21. Line 162: Consider “…among women (B=1.42, p = 0.86; Table 2).” Rather than having brackets back to back. Same on line 166 and 172.

Response:

I checked throughout the result section and made changes as you suggested where applicable.

#22. Line 164-165: report df for genotypes and for M&F for the genotypes on line 169-172.

Response:

I showed t-statistics and p-values in the results section. P-values are derived from t-statistics and the degree of freedom; therefore we avoided showing the degree of freedom here since it is redundant.

#23. Line 190 (OXTR discussion): consider also OXTR has been shown to be linked with social attention in rhesus macaques (Howarth et al., 2023;10.1371/journal.pone.0288108) suggesting that this is a well conserved social response across species.

Response:

Thank you for showing the important literature. I am aware of the importance of being supported in animal experiments and included the argument regarding the suggested literature in the discussion.

“The association between OXTR and social attention was also shown in an animal experiment [44], suggesting this as a well-conserved social response across species.” (Discussion: paragraph 2)

#24. Line 219: A allele carries for OXTR rs53576 were also had lower level of optimism and self-esteem (Saphire-Bernstein et al., 2011; https://doi.org/10.1073/pnas.1113137108) and have poor social recognition (Skuse et al., 2014; 10.1073/pnas.1302985111).

Response:

Thank you for showing the important literature to be included in the manuscript. We added this research.

“For example, in one study OXTR rs53576 A allele carriers showed more social connectedness [14] while in another study A allele carriers exhibited lower empathy [15] and lower levels o

Attachment Submitted filename: Response to Reviewers.docx

10.1371/journal.pone.0308728.r003
Decision Letter 1
Kavushansky Alexandra Academic Editor
© 2024 Alexandra Kavushansky
2024
Alexandra Kavushansky
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version1
30 Jul 2024

Epistatic interactions between oxytocin- and dopamine-related genes and trust

PONE-D-23-41164R1

Dear Dr. Fujiwara,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Alexandra Kavushansky, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

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10.1371/journal.pone.0308728.r004
Acceptance letter
Kavushansky Alexandra Academic Editor
© 2024 Alexandra Kavushansky
2024
Alexandra Kavushansky
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
5 Aug 2024

PONE-D-23-41164R1

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References

1 Claessens S , Fischer K , Chaudhuri A , Sibley CG , Atkinson QD . The dual evolutionary foundations of political ideology. Nature human behaviour. 2020;4 : 336–345. doi: 10.1038/s41562-020-0850-9 32231279
2 Yamagishi T. Trust: The evolutionary game of mind and society. Springer; 2011.
3 McKnight DH , Choudhury V , Kacmar C . Developing and validating trust measures for e-commerce: An integrative typology. Information systems research. 2002;13 : 334–359.
4 Kramer RM . Trust and distrust in organizations: Emerging perspectives, enduring questions. Annu Rev Psychol. 1999;50 : 569–598. doi: 10.1146/annurev.psych.50.1.569 15012464
5 Robbins BG . From the general to the specific: How social trust motivates relational trust. Soc Sci Res. 2016;55 : 16–30. doi: 10.1016/j.ssresearch.2015.09.004 26680285
6 Cesarini D , Dawes CT , Fowler JH , Johannesson M , Lichtenstein P , Wallace B . Heritability of cooperative behavior in the trust game. Proc Natl Acad Sci U S A. 2008;105 : 3721–3726. doi: 10.1073/pnas.0710069105 18316737
7 Lieberwirth C , Wang Z . Social bonding: regulation by neuropeptides. Front Neurosci. 2014;8 : 171. doi: 10.3389/fnins.2014.00171 25009457
8 Oxytocin Feldman R. and social affiliation in humans. Horm Behav. 2012;61 : 380–391.22285934
9 Kosfeld M , Heinrichs M , Zak PJ , Fischbacher U , Fehr E . Oxytocin increases trust in humans. Nature. 2005;435 : 673–676. doi: 10.1038/nature03701 15931222
10 Feldman R , Monakhov M , Pratt M , Ebstein RP . Oxytocin Pathway Genes: Evolutionary Ancient System Impacting on Human Affiliation, Sociality, and Psychopathology. Biol Psychiatry. 2016;79 : 174–184. doi: 10.1016/j.biopsych.2015.08.008 26392129
11 Skuse DH , Gallagher L . Genetic influences on social cognition. Pediatr Res. 2011;69 : 85R–91R. doi: 10.1203/PDR.0b013e318212f562 21289535
12 Johnson ZV , Young LJ . Oxytocin and vasopressin neural networks: Implications for social behavioral diversity and translational neuroscience. Neurosci Biobehav Rev. 2017;76 : 87–98. doi: 10.1016/j.neubiorev.2017.01.034 28434591
13 Pearce E , Wlodarski R , Machin A , Dunbar RIM . Variation in the β-endorphin, oxytocin, and dopamine receptor genes is associated with different dimensions of human sociality. Proc Natl Acad Sci U S A. 2017;114 : 5300–5305.28461468
14 Chang S-C , Glymour MM , Rewak M , Cornelis MC , Walter S , Koenen KC , et al . Are genetic variations in OXTR, AVPR1A, and CD38 genes important to social integration? Results from two large U.S. cohorts. Psychoneuroendocrinology. 2014;39 : 257–268. doi: 10.1016/j.psyneuen.2013.09.024 24209975
15 Rodrigues SM , Saslow LR , Garcia N , John OP , Keltner D . Oxytocin receptor genetic variation relates to empathy and stress reactivity in humans. Proc Natl Acad Sci U S A. 2009;106 : 21437–21441. doi: 10.1073/pnas.0909579106 19934046
16 Saphire-Bernstein S , Way BM , Kim HS , Sherman DK , Taylor SE . Oxytocin receptor gene (OXTR) is related to psychological resources. Proc Natl Acad Sci U S A. 2011;108 : 15118–15122. doi: 10.1073/pnas.1113137108 21896752
17 Nishina K , Takagishi H , Inoue-Murayama M , Takahashi H , Yamagishi T . Polymorphism of the Oxytocin Receptor Gene Modulates Behavioral and Attitudinal Trust among Men but Not Women. PLoS One. 2015;10 : e0137089. doi: 10.1371/journal.pone.0137089 26444016
18 Liu J , Gong P , Li H , Zhou X . A field study of the association between CD38 gene and altruistic behavior: Empathic response as a mediator. Psychoneuroendocrinology. 2017;85 : 165–171. doi: 10.1016/j.psyneuen.2017.08.010 28865941
19 Huetter FK , Moehlendick B , Knop D , Siffert W . Lack of association of common polymorphisms linked to empathic behavior with self-reported trait empathy in healthy volunteers. Horm Behav. 2020;126 : 104841. doi: 10.1016/j.yhbeh.2020.104841 32828797
20 Sadikaj G , Moskowitz DS , Zuroff DC , Bartz JA . CD38 is associated with communal behavior, partner perceptions, affect and relationship adjustment in romantic relationships. Sci Rep. 2020;10 : 12926. doi: 10.1038/s41598-020-69520-y 32820186
21 Feldman R , Zagoory-Sharon O , Weisman O , Schneiderman I , Gordon I , Maoz R , et al . Sensitive parenting is associated with plasma oxytocin and polymorphisms in the OXTR and CD38 genes. Biol Psychiatry. 2012;72 : 175–181. doi: 10.1016/j.biopsych.2011.12.025 22336563
22 Klein MO , Battagello DS , Cardoso AR , Hauser DN , Bittencourt JC , Correa RG . Dopamine: Functions, Signaling, and Association with Neurological Diseases. Cell Mol Neurobiol. 2019;39 : 31–59. doi: 10.1007/s10571-018-0632-3 30446950
23 Skuse DH , Gallagher L . Dopaminergic-neuropeptide interactions in the social brain. Trends Cogn Sci. 2009;13 : 27–35. doi: 10.1016/j.tics.2008.09.007 19084465
24 Baskerville TA , Douglas AJ . Dopamine and oxytocin interactions underlying behaviors: potential contributions to behavioral disorders. CNS Neurosci Ther. 2010;16 : e92–123. doi: 10.1111/j.1755-5949.2010.00154.x 20557568
25 Love TM , Enoch M-A , Hodgkinson CA , Peciña M , Mickey B , Koeppe RA , et al . Oxytocin gene polymorphisms influence human dopaminergic function in a sex-dependent manner. Biol Psychiatry. 2012;72 : 198–206. doi: 10.1016/j.biopsych.2012.01.033 22418012
26 Groppe SE , Gossen A , Rademacher L , Hahn A , Westphal L , Gründer G , et al . Oxytocin influences processing of socially relevant cues in the ventral tegmental area of the human brain. Biol Psychiatry. 2013;74 : 172–179. doi: 10.1016/j.biopsych.2012.12.023 23419544
27 Sauer C , Montag C , Reuter M , Kirsch P . Imaging oxytocin × dopamine interactions: an epistasis effect of CD38 and COMT gene variants influences the impact of oxytocin on amygdala activation to social stimuli. Front Neurosci. 2013;7 : 45.23554586
28 Kohli S , King MV , Williams S , Edwards A , Ballard TM , Steward LJ , et al . Oxytocin attenuates phencyclidine hyperactivity and increases social interaction and nucleus accumben dopamine release in rats. Neuropsychopharmacology. 2019;44 : 295–305. doi: 10.1038/s41386-018-0171-0 30120410
29 László K , Péczely L , Géczi F , Kovács A , Zagoracz O , Ollmann T , et al . The role of D2 dopamine receptors in oxytocin induced place preference and anxiolytic effect. Horm Behav. 2020;124 : 104777. doi: 10.1016/j.yhbeh.2020.104777 32439347
30 Dumais KM , Veenema AH . Vasopressin and oxytocin receptor systems in the brain: Sex differences and sex-specific regulation of social behavior. Front Neuroendocrinol. 2016;40 : 1–23. doi: 10.1016/j.yfrne.2015.04.003 25951955
31 Trainor BC . Stress responses and the mesolimbic dopamine system: social contexts and sex differences. Horm Behav. 2011;60 : 457–469. doi: 10.1016/j.yhbeh.2011.08.013 21907202
32 Fujiwara T , Weisman O , Ochi M , Shirai K , Matsumoto K , Noguchi E , et al . Genetic and peripheral markers of the oxytocin system and parental care jointly support the cross-generational transmission of bonding across three generations. Psychoneuroendocrinology. 2019;102 : 172–181. doi: 10.1016/j.psyneuen.2018.12.004 30572177
33 Wade M , Hoffmann TJ , Wigg K , Jenkins JM . Association between the oxytocin receptor (OXTR) gene and children’s social cognition at 18 months. Genes Brain Behav. 2014;13 : 603–610. doi: 10.1111/gbb.12148 24916666
34 Creswell KG , Wright AGC , Troxel WM , Ferrell RE , Flory JD , Manuck SB . OXTR polymorphism predicts social relationships through its effects on social temperament. Soc Cogn Affect Neurosci. 2015;10 : 869–876. doi: 10.1093/scan/nsu132 25326040
35 Champely S. pwr: Basic Functions for Power Analysis. 2020. Available: https://CRAN.R-project.org/package=pwr.
36 Yamagishi T , Yamagishi M . Trust and commitment in the United States and Japan. Motiv Emot. 1994;18 : 129–166.
37 Oecd. OECD Guidelines on Measuring Trust. OECD; 2017.
38 Westfall THFB . Simultaneous Inference in General Parametric Models. Biometrical Journal. 2008;50 : 3446–3363. doi: 10.1002/bimj.200810425 18481363
39 R core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2023. Available: https://www.r-project.org/.
40 Schneiderman I , Kanat-Maymon Y , Ebstein RP , Feldman R . Cumulative risk on the oxytocin receptor gene (OXTR) underpins empathic communication difficulties at the first stages of romantic love. Soc Cogn Affect Neurosci. 2014;9 : 1524–1529. doi: 10.1093/scan/nst142 23974948
41 Wu N , Li Z , Su Y . The association between oxytocin receptor gene polymorphism (OXTR) and trait empathy. J Affect Disord. 2012;138 : 468–472. doi: 10.1016/j.jad.2012.01.009 22357335
42 Waller R , Corral-Frías NS , Vannucci B , Bogdan R , Knodt AR , Hariri AR , et al . An oxytocin receptor polymorphism predicts amygdala reactivity and antisocial behavior in men. Soc Cogn Affect Neurosci. 2016;11 : 1218–1226. doi: 10.1093/scan/nsw042 27036876
43 Israel S , Lerer E , Shalev I , Uzefovsky F , Riebold M , Laiba E , et al . The oxytocin receptor (OXTR) contributes to prosocial fund allocations in the dictator game and the social value orientations task. PLoS One. 2009;4 : e5535. doi: 10.1371/journal.pone.0005535 19461999
44 Howarth ERI , Szott ID , Witham CL , Wilding CS , Bethell EJ . Genetic polymorphisms in the serotonin, dopamine and opioid pathways influence social attention in rhesus macaques (Macaca mulatta). PLoS One. 2023;18 : e0288108. doi: 10.1371/journal.pone.0288108 37531334
45 Fukuyama F. Trust: The social virtues and the creation of prosperity. Free press New York; 1995.
46 Reuter M , Felten A , Penz S , Mainzer A , Markett S , Montag C . The influence of dopaminergic gene variants on decision making in the ultimatum game. Front Hum Neurosci. 2013;7 : 242. doi: 10.3389/fnhum.2013.00242 23759976
47 Zhang L , Hu L , Li X , Zhang J , Chen B . The DRD2 rs1800497 polymorphism increase the risk of mood disorder: evidence from an update meta-analysis. J Affect Disord. 2014;158 : 71–77. doi: 10.1016/j.jad.2014.01.015 24655768
48 Chang WH , Lee IH , Chen KC , Chi MH , Chiu N-T , Yao WJ , et al . Oxytocin receptor gene rs53576 polymorphism modulates oxytocin-dopamine interaction and neuroticism traits—a SPECT study. Psychoneuroendocrinology. 2014;47 : 212–220. doi: 10.1016/j.psyneuen.2014.05.020 25001970
49 Colombo M. Deep and beautiful. The reward prediction error hypothesis of dopamine. Stud Hist Philos Biol Biomed Sci. 2014;45 : 57–67. doi: 10.1016/j.shpsc.2013.10.006 24252364
50 Borland JM , Rilling JK , Frantz KJ , Albers HE . Sex-dependent regulation of social reward by oxytocin: an inverted U hypothesis. Neuropsychopharmacology. 2019;44 : 97–110. doi: 10.1038/s41386-018-0129-2 29968846
51 Archer J. The reality and evolutionary significance of human psychological sex differences. Biol Rev Camb Philos Soc. 2019;94 : 1381–1415. doi: 10.1111/brv.12507 30892813
52 Egli T , Vukojevic V , Sengstag T , Jacquot M , Cabezón R , Coynel D , et al . Exhaustive search for epistatic effects on the human methylome. Sci Rep. 2017;7 : 13669. doi: 10.1038/s41598-017-13256-9 29057891
53 Reuter M , Schmitz A , Corr P , Hennig J . Molecular genetics support Gray’s personality theory: the interaction of COMT and DRD2 polymorphisms predicts the behavioural approach system. Int J Neuropsychopharmacol. 2006;9 : 155–166. doi: 10.1017/S1461145705005419 15896265
54 Scatliffe N , Casavant S , Vittner D , Cong X . Oxytocin and early parent-infant interactions: A systematic review. International journal of nursing sciences. 2019;6 : 445–453. doi: 10.1016/j.ijnss.2019.09.009 31728399
