No links between genetic variation and developing theory of mind: A preregistered replication attempt of candidate gene studies

Theory of Mind: A Brief Review of Candidate Genes

Deficits in theory of mind (ToM), known as the ability to understand the other's mind, have been associated with several psychopathological outcomes. The present systematic review aims to summarize the results of genetic studies that investigated gene polymorphisms associated with mentalization performance tasks in children and adults. The systematic review was carried out following PRISMA guidelines, and the literature search was conducted in PubMed and EBSCOhost using the following keywords: 'theory of mind, mentalizing, mindreading' and 'gene, genetic basis'. Nineteen studies met the eligibility criteria for inclusion. Most of the literature focused on the role of DRD4, DAT1, OXTR, OXT, COMT, ZNF804A, AVP, AVPR, SCL6A4, EFHC2, MAO-A, and the family of GTF2I genes in influencing ToM. However, controversial results emerged in sustaining the link between specific genetic polymorphisms and mentalization abilities in children and adults. Available data show heterogeneous outcomes, with studies reporting an association between the same family genes in subjects of the same age and other studies reporting no correlation. This does not allow us to draw any solid conclusions but paves the way for exploring genes involved in ToM tasks.

Association of verbal and non-verbal theory of mind abilities with non-coding variants of OXTR in youth with autism spectrum disorder and typically developing individuals: a case-control study

BACKGROUND

The ability to attribute mental states to others is called theory of mind (ToM) and is a substantial component of social cognition. This ability is abnormally developed in individuals with autism spectrum disorder (ASD). Several studies over the past decade have identified the oxytocin receptor gene (OXTR) and its variants as promising components for explaining the molecular mechanisms underlying Theory of Mind (ToM). The main aim of this study is to examine the association between rs2268498 and rs53576, two functional single nucleotide polymorphisms (SNPs), and verbal and non-verbal ToM in children and adolescents with ASD and a group of typically developing youth.

METHODS

The study involved 44 children and adolescents with high-functioning ASD aged 8 to 18 years old and 44 TD individuals who were matched on age and sex. In all participants, blood samples were collected and rs2268498 and rs53576 were genotyped. Happe's Strange Stories test and the moving shapes paradigm were used to measure verbal and non-verbal ToM in all participants.

RESULTS

The results of permutation tests and logistic regression suggested that in TD group, rs2268498 AA carriers showed significant higher scores in variables representing verbal ToM (ToM stories and appropriateness score) whereas, in ASD group, rs53576 AA carriers exhibited significant better performance in parameters related to non-verbal ToM (ToM general rule and intentionality score). The results of hierarchical clustering in both groups support the findings by distinguishing between language-related and language-independent aspects of ToM.

CONCLUSIONS

In the present study, we examined the association between rs2268498 and rs53576 and social functioning in individuals with ASD and TD group. We found preliminary evidence that rs2268498 and rs53576 are associated with ToM related abilities in healthy individuals as well as in autistic individuals. Accordingly, rs2268498 and rs53576 may play an important role in predicting ToM capabilities. It will be necessary to conduct further research to address the association of genetic variants with a deficit in ToM in individuals with ASD.

Detection, processing and reinforcement of social cues: regulation by the oxytocin system

Many social behaviours are evolutionarily conserved and are essential for the healthy development of an individual. The neuropeptide oxytocin (OXT) is crucial for the fine-tuned regulation of social interactions in mammals. The advent and application of state-of-the-art methodological approaches that allow the activity of neuronal circuits involving OXT to be monitored and functionally manipulated in laboratory mammals have deepened our understanding of the roles of OXT in these behaviours. In this Review, we discuss how OXT promotes the sensory detection and evaluation of social cues, the subsequent approach and display of social behaviour, and the rewarding consequences of social interactions in selected reproductive and non-reproductive social behaviours. Social stressors - such as social isolation, exposure to social defeat or social trauma, and partner loss - are often paralleled by maladaptations of the OXT system, and restoring OXT system functioning can reinstate socio-emotional allostasis. Thus, the OXT system acts as a dynamic mediator of appropriate behavioural adaptations to environmental challenges by enhancing and reinforcing social salience and buffering social stress.

Understanding altruistic behavior: The joint role of prefrontal damage and OXTR genotype

Altruism is a type of prosocial behavior that is carried out in the absence of personal benefit or even at an expense to self. Trait altruism varies greatly across individuals, and the reasons for this variability are still not fully understood. Growing evidence suggests that altruism may be partly determined by the oxytocin receptor (OXTR) gene, which regulates the emotions underlying altruistic attitudes, such as empathy and trust. Neuroimaging and lesion studies have also implied several higher-order brain regions, including the prefrontal cortex, in altruistic behaviors. Yet the existing reports are contradictory and suggest that the top-down control exercised by the prefrontal cortex may promote both altruistic and self-interested behaviors and, thus, could obscure one's natural proclivity towards altruism encoded by OXTR. Here, we hypothesized that extensive prefrontal damage would result in an increased influence of the OXTR genotype on one's altruistic attitudes and actions. To test this hypothesis, we recruited 115 male combat veterans with penetrating traumatic brain injury to the prefrontal cortex and other brain regions, as well as 35 demographically matched control subjects without brain injury. Participants completed a self-report altruism questionnaire and were genotyped for four OXTR single nucleotide polymorphisms implicated in prosocial behavior, including rs53576, rs1042778, rs2254298 and rs7632287. Consistent with the previous studies, we found that individuals homozygotic for the G allele of rs53576 and rs7632287 were significantly more altruistic than carriers of at least one "vulnerable" A allele. Remarkably, in patients with prefrontal cortex damage, greater lesion extent was associated with significantly lower altruism scores in carriers of the A allele of rs7632287, but not in G-homozygotes, suggesting that significant disruption of the prefrontal cortex increased the influence of genetic polymorphisms on prosocial behavior. This study presents the first account of an interaction effect between the OXTR genotype and the location and extent of brain damage.

Oxytocin—a social peptide? Deconstructing the evidence

In this paper, we analyse the claim that oxytocin is a ‘social neuropeptide’. This claim originated from evidence that oxytocin was instrumental in the initiation of maternal behaviour and it was extended to become the claim that oxytocin has a key role in promoting social interactions between individuals. We begin by considering the structure of the scientific literature on this topic, identifying closely interconnected clusters of papers on particular themes. We then analyse this claim by considering evidence of four types as generated by these clusters: (i) mechanistic studies in animal models, designed to understand the pathways involved in the behavioural effects of centrally administered oxytocin; (ii) evidence from observational studies indicating an association between oxytocin signalling pathways and social behaviour; (iii) evidence from intervention studies, mainly involving intranasal oxytocin administration; and (iv) evidence from translational studies of patients with disorders of social behaviour. We then critically analyse the most highly cited papers in each segment of the evidence; we conclude that, if these represent the best evidence, then the evidence for the claim is weak.

This article is part of the theme issue ‘Interplays between oxytocin and other neuromodulators in shaping complex social behaviours’.