The nonapeptide oxytocin (OXT) and its receptor (OXTR) have been implicated in social cognition, empathy, emotion and stress regulation in humans. Previous studies reported associations between OXT and OXTR genetic polymorphisms and risk for disorders characterized by impaired socio-emotional functioning, such as schizophrenia and autism. Here we investigate the influence of two single nucleotide polymorphisms (SNPs) within the OXTR gene on a measure of socio-emotional functioning in schizophrenic patients. OXTR SNPs that were previously investigated in other studies were genotyped in 145 patients diagnosed with schizophrenia according to DSM-IV and 145 healthy controls matched for age and gender. The Interpersonal Reactivity Index (IRI) was used to assess cognitive (‘perspective taking’), affective (‘empathic concern’) and self-related (‘personal distress’) dimensions of empathy. No group differences in genotype frequencies were observed. MANCOVA revealed a significant main (F [1,282] = 10.464; p<0.01) and interaction effect (genotype by diagnosis: F [1,282] = 4.329; p<0.05) of OXTR SNP rs2254298(A>GG) with ‘empathic concern’. Within the schizophrenia group, linear regression analysis determined OXTR rs2254298 genotype, PANSS negative and general symptom score, and age of disease onset as being significantly associated with ‘empathic concern’. OXTR rs2254298 significantly impacted PANSS general psychopathology scores. No associations were found for OXTR rs53576, IRI ‘perspective taking’ or ‘personal distress’ ratings. Our preliminary findings support hypotheses about an involvement of OXTR rs2254298 in emotional empathy in schizophrenic and healthy individuals, warranting independent replication.
Citation: Montag C, Brockmann E-M, Lehmann A, Müller DJ, Rujescu D, Gallinat J (2012) Association between Oxytocin Receptor Gene Polymorphisms and Self-Rated ‘Empathic Concern’ in Schizophrenia. PLoS ONE 7(12): e51882. doi:10.1371/journal.pone.0051882
Editor: Andreas Reif, University of Wuerzburg, Germany
Received: June 29, 2012; Accepted: November 7, 2012; Published: December 20, 2012
Copyright: © 2012 Montag et al. 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.
Funding: This work was supported by Canadian Institues of Health Research Michael Smith New Investigator Salary Prize for Research in Schizophrenia to DJM, and Ontario Mental Health Foundation New Investigator Fellowship to DJM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.
Competing interests: The authors have declared that no competing interests exist.
Social-cognitive deficits are an important clinical feature of schizophrenia and have drawn much attention over the past decades  as disturbances of the ‘social brain’ essentially impact psychosocial proficiency ,  and might represent trait-markers for this disease . While a large body of evidence confirms impairments of theory of mind – and of various aspects of emotion processing , , research on empathy in the narrow sense has been published less frequently in schizophrenia , .
Across species, a broad spectrum of social and emotional behaviors is modulated by the neurohormone oxytocin (OXT) –. OXT is produced in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). Their magnocellular neurons mainly project to the neurohypophysis, whereas central OXT, after its axonal or somatodendritic release, can modulate functional activity in many brain regions including cortical areas, amygdala, striatum, nucleus accumbens, hippocampus, ventral tegmental area and brainstem nuclei –. Animal studies demonstrate that OXT stimulates not only reproductive behaviors, but also has positive effects on social recognition, affiliation and approach behavior while alleviating social stress and anxiety , , , , –. In humans, a substantial body of research indicates its regulative function for social cognition –, social memory –, prosocial behavior –, attachment  and trust . Specifically, OXT has been shown to dampen the hypothalamic-pituitary-adrenal-axis (HPA-axis) ,  and to reduce amygdala activation in response to social stressors –. Of note, OXT interacts with the dopaminergic system and thus stimulates the attribution of salience to social and emotional stimuli –.
Alterations of the central oxytocinergic system might play a role in the pathogenesis of disorders marked by social deficits such as schizophrenia or modulate their presentation . This assumption is supported by preliminary evidence about beneficial effects of high plasma OXT levels – or intranasal OXT administration on psychotic symptoms – and also on theory of mind, social perception ,  or verbal memory  in schizophrenia. Evidence from animal studies suggests a role of OXT as a mediator of second-generation antipsychotic action , , and its ability to restore glutamatergic dysfunction induced by NMDA-receptor-antagonists , .
Beside peripheral OXT concentrations, variations of the OXTR gene might contribute to explain variability of core socio-emotional processes and related phenotypes. OXTR has been discussed as a candidate gene for autism spectrum vulnerability –, but until to date only few studies have investigated variations of oxytocinergic system genes in schizophrenia –. Souza et al. first reported the association of three OXT polymorphisms with the diagnosis of schizophrenia (rs4813625, rs3761248 in a case-control, and nominal over-transmission of rs2740204 in a family-based study) . OXT SNP rs2740204 was shown to be related to clozapine treatment response, while OXTR variants were associated to overall symptoms (rs237885, rs237887) and improvement in positive symptoms (rs11706648, rs4686301, rs237899) . Teltsh et al. determined three SNPs within the OXT-AVP cluster (rs4813626, rs2740204, AVP3011589) that were associated with schizophrenia in a family-based association study . Montag et al. identified OXTR SNP rs53576(A) as being linked to the disease in a case-control study of 406 schizophrenic and 406 healthy individuals; rs53576 was associated with PANSS general psychopathology, and rs237902 with negative symptoms .
However, this study sets out to explore potential associations of trait empathy in schizophrenic and healthy individuals with two selected OXTR SNPs - both situated in the third intron of OXTR - that were consistently linked to socio-emotional phenotypes before. Beside the single report of being associated with schizophrenia , OXTR rs53576 was suggested to mediate dispositional empathy , social stress reactivity –, prosocial attitude , social support seeking  and trust , while OXTR rs2254298 was associated with cognitive empathy in healthy individuals . OXTR rs2254298 ,  as well as rs53576 ,  were linked to attachment measures and parental sensitivity. Both OXTR SNPs were also hypothesized to be associated with unipolar depression  and with risk for autism spectrum disorder , , , , . Moreover, our selection of SNPs was guided by recent evidence from imaging studies indicating an impact of OXTR rs2254298 – and OXTR rs53576  on key oxytocinergic structures including the amygdala and the hypothalamus. Trait empathy was examined using the Interpersonal Reactivity Index  which covers three essential dimensions of empathic responding - the cognitive facet of empathy (‘perspective taking’) as well as altruistic concern (‘empathic concern’) and the self-directed, aversive experience of social distress (‘personal distress’). We hypothesized that OXTR risk allele carriers would show deficits in self-rated empathic dimensions.
Materials and Methods
The study was approved by the local ethics committee (Charité Universitätsmedizin Berlin, Germany). All subjects gave written informed consent. The study was conducted according to the principles expressed in the Declaration of Helsinki. All potential participants who declined to participate or otherwise did not participate were eligible for treatment and were not disadvantaged in any other way by not participating in the study.
Only patients with an unaltered capacity to consent were included in the study. Capacity to consent was confirmed during the screening process by both the treating physician, who was not involved in the study, and C.M. according to the criteria developed by .
Schizophrenic subjects (n = 145), aged between 18 and 69 years, recruited from the Department of Psychiatry, Charité Universitätsmedizin Berlin, Campus Mitte, participated in the study. Diagnosis was confirmed using the Structured Clinical Interview for DSM-IV (SCID-I; German version) ; symptom severity was assessed with the Positive and Negative Syndrome Scale . Healthy control subjects (n = 145) were recruited by newspaper advertisements and screened by trained psychiatrists with a structured interview (M.I.N.I.) . All together, normal controls were matched to the patients’ sample according to age and gender. All participants were of European descent and not related to each other. Exclusion criteria for both groups were DSM-IV axis-I or axis-II disorders (except schizophrenia for the patient group). Controls reporting axis-I mental disorders in their first- or second degree relatives were excluded. The partial overlap of the study sample with the participants of a previous study  was limited by the availability of data on empathy, and only a fraction of participants could be retrieved to take part in the current project. Moreover, OXTR SNP rs2254298 had not been genotyped at the time, when  was prepared. EDTA blood was taken from all participants for genotyping. Clinical types of schizophrenia according to DSM-IV-TR were as follows: paranoid (n = 128), undifferentiated (n = 5), disorganized (n = 4), catatonic (n = 3), residual (n = 1), and in n = 4 schizoaffective disorder was reported.
DNA extraction was done with the QIAamp Blood Maxi Kit (QIAamp DNA Blood Midi/Maxi Handbook, Firma Qiagen, Hilden, Germany, 2005). DNA concentration was adjusted using the PicoGreen quantitation reagent (Invitrogen, Karlsruhe, Germany). One ng DNA was genotyped using the iPLEX assay on the MassARRAY MALDI-TOF mass spectrometer (SEQUENOM, Hamburg, Germany). Genotyping call rates in cases and controls were all >99%. Allele frequencies were similar to CEU sample frequencies (www.hapmap.org).
Interpersonal Reactivity Index
The Interpersonal Reactivity Index (IRI)  assesses aspects of empathic responding, which were determined by factor analysis. We used the German translation (‘Saarbrücker Persönlichkeitsfragebogen’; SPF) . For analysis, three relevant IRI-subscales were used: ‘Perspective taking’ refers to the tendency to spontaneously adopt the psychological point of view of others and to reason about their mental states. The ‘empathic concern’ scale comprises respondents’ prosocial feelings of warmth, compassion and concern for others. ‘Personal distress’ measures self-oriented feelings of anxiety and discomfort in response to the distress of others. Construct validity, internal consistency the IRI scales  and its feasibility in schizophrenic patients were supported in several studies , , .
General Cognitive Function
A multiple choice vocabulary test (Mehrfachwahlwortschatztest, MWT-B)  was applied to estimate verbal intelligence.
These were carried out as indicated in the results section using PASW for Windows 20.0® and code for mediation analysis available from http://www.afhayes.com/ . Statistical significance was set at p<0.05. Genotypes were tested to conform to the Hardy-Weinberg-equilibrium using HWSIM Software (http://krunch.med.yale.edu/hwsim/). Allelic and genotypic distributions and odds ratios (OR) between patients and controls were examined by Pearson χ2 test on 2×2 contingency tables. Multivariate analysis of variance and linear regression analyses were performed as described in the following section. Because of the low minor allele frequency of OXTR rs2254298 AA genotype (n = 2 in each group) and of OXTR rs53576 AA genotype (schizophrenia: n = 7; controls: n = 13) they were combined with the heterozygotes for statistical analyses in a presumably dominant genetic model.
Demographic data and disease characteristics of schizophrenic participants are given in Table 1. Schizophrenia patients and healthy controls differed significantly in verbal IQ and educational years. All genotype frequencies of rs2254298 and rs53576 were in accordance with the Hardy-Weinberg-equilibrium in the schizophrenic, healthy and combined samples (p>0.05). As for OXTR rs2254298, A-allele frequencies were 0.11 in the schizophrenia and 0.10 in the healthy sample; for OXTR rs53576, A-allele frequencies were 0.32 in the schizophrenia and 0.29 in the healthy sample. Chi-squared tests revealed no significant differences of genotype distributions and allele frequencies for the studied SNPs between groups, and frequencies were also unrelated to gender in the overall sample (χ2 test, p>0.05). However, in the patients group, the AA- or AG-genotype of rs2254298 was significantly more common in males than in females (χ2 = 5.379, p = 0.020).
As for the IRI results, schizophrenia patients showed significantly lower scores for ‘perspective taking’ scores and higher scores for ‘personal distress’ than healthy individuals (Table 2). T-tests revealed no differences between sexes in either group (t-test for independent samples, p>0.05).
OXTR Polymorphisms, IRI Dimensions of Empathy and Diagnostic Group
Schizophrenic patients carrying one or two OXTR rs2254298 A-alleles showed significantly more ‘empathic concern’ than those carrying two G-alleles (Table 3; Figure 1). Multivariate analysis of covariance (MANCOVA) was computed to determine main and interaction effects of rs2254298 and rs53576 genotypes, and diagnosis as factors, as well as the covariate verbal IQ on the three relevant IRI scores as dependent variables (‘perspective taking’, ‘empathic concern’, ‘personal distress’). Homoscedasticity of samples was confirmed by Box-M and Levene tests (p>0.05). Significant overall effects were detected for OXTR rs2254298, diagnostic group, and IQ; the interaction between OXTR rs2254298 genotype and diagnosis was significant (Table 4). Post-hoc analyses indicated higher IRI ‘empathic concern’ in the combined OXTR AA/AG-genotype (mean = 27.1, SD = 4.1) compared to GG (mean = 25.1, SD = 4.0). The variable diagnostic group showed significant impact on ‘perspective taking’ (SZ: mean = 23.1, SD = 4.7; HC: mean = 24.6, SD = 3.8) and on ‘personal distress’ (SZ: mean = 20.1, SD = 4.6; HC: mean = 15.8, SD = 4.3). Diagnosis showed no significant main effect on ‘empathic concern’, but schizophrenic patients carrying one or two A-alleles of OXTR rs2254298 showed highest ‘empathic concern’ compared to all the other groups. Verbal IQ was positively associated with IRI ‘perspective taking’. As the introduction of gender as an additional factor would have led to small cell sizes and heterogeneity of covariance matrices, another MANCOVA was performed to determine the influence of gender, OXTR rs2254298 and diagnosis on ‘empathic concern’ scores, while controlling for cognition more strictly (factors: OXTR rs2254298, gender and diagnosis; covariates: verbal IQ and educational years). While females showed significantly higher values of IRI ‘empathic concern’ and ‘personal distress’, the significant impact of OXTR rs2254298 on ‘empathic concern’ remained, and there was no significant interaction between gender and OXTR rs2254298. (supporting information: Table S1).
Self-rated IRI ‘empathic concern’ scores are significantly higher in schizophrenic patients endowed with an OXTR SNP rs2254298 AA- or AG-genotype compared to GG-genotype carriers (n = 145; mean, SD; t-test for independent samples, ***: p<0.001), while no significant differences between genotypes are detected in healthy controls (n = 145; p>0.05).
OXTR Polymorphisms, Disease Characteristics and Empathy in Schizophrenia Patients
Within the patient group, carriers of AA/AG- versus GG-genotypes of OXTR SNP rs2254298 and OXTR SNP rs53576, respectively, did not differ with respect to age, verbal IQ, educational years, age at disease onset, duration of illness, first- and second-generation antipsychotic daily dose and cumulative treatment years with antipsychotics (t-test for independent samples, p>0.05). As for the impact of OXTR SNPs rs2254298 and rs53576 on psychopathological symptom severity, t-tests for independent samples indicated significantly higher values on the PANSS general psychopathology score in patients endowed with one or two A-alleles of rs2254298 (T = −2.355; p = 0.020) (Figure 2). No significant group differences were detected for the other PANSS scores and for rs53576.
Schizophrenic patients carrying AA- or AG-genotypes of OXTR rs2254298 show significantly higher PANSS general psychopathology scores than GG-carriers (n = 145; mean, SD; t-test for independent samples, *: p<0.05).
To explore the association between OXTR polymorphisms and self-rated empathy, linear regression analyses were performed. Dependent variables were the three IRI scores, independent variables were OXTR rs2254289 and rs53576 polymorphisms, gender, age at first manifestation, duration of illness, PANSS positive, negative and general scores. As for IRI ‘empathic concern’, the model predicted 18.1% of total variance (F[8; 136] = 4.979, p<0.001). Significant predictors of ‘empathic concern’ were OXTR rs2254298 genotype (β = −0.307, p<0.001), age at first manifestation (β = 0.197, p = 0.017), PANSS negative score (β = −0.414, p<0.001) and PANSS general psychopathology score (β = 0.313, p = 0.025). OXT rs53576 polymorphism, gender, duration of illness and PANSS positive score were not significant as independent predictors. The model was not significant for IRI ‘perspective taking’ or IRI ‘personal distress’ as dependent variables.
To explore possible indirect effects of OXTR rs2254298 polymorphisms on ‘empathic concern’ through partial mediation by PANSS general or negative scores, or age of onset of schizophrenia, mediation analysis  was conducted. OXTR rs2254298 significantly predicted PANSS general psychopathology scores (β = −0.193, p = 0.020), but it showed only a trend on PANSS negative symptoms (β = −0.151, p = 0.070) and no effect on age of onset of schizophrenia (β = −0.037, p = 0.663). Comparisons of the direct effects of OXTR rs2254298 on IRI ‘empathic concern’ (β = −0.280, p<0.001) and β-values from simultaneous regression of IRI ‘empathic concern’ on OXTR rs2254298 including each of the 3 potential mediators as additional independents did not indicate mediation effects (with PANSS general psychopathology: β = −0.287, p<0.001; with PANSS negative: β = −0.315, p<0.001; with age of onset: β = −0.273, p<0.001). Moreover, no significant indirect effect could be determined by calculating Sobel’s Z-values in a multiple mediator model (p>0.05) .
The potential relationship of allelic variations of OXTR rs2254298 and rs53576 with various psychopathological or temperamental conditions has been investigated in several studies. In this study, we compared basic empathy dimensions and two SNPs within the OXTR gene in schizophrenic patients and healthy controls. Group comparisons of the IRI empathy scores revealed significantly lower self-report ‘perspective taking’ and higher ‘personal distress’ scores in schizophrenia patients compared to controls, replicating our previous finding in a larger independent sample . However, the main result is a significant main effect of OXTR rs2254298 as well as a significant interaction between diagnosis and OXTR rs2254298 on IRI ‘empathic concern’, with schizophrenic patients carrying an AA- or AG-genotype showing highest IRI values.
Our findings might corroborate previous research indicating a possible genetic contribution of OXTR polymorphisms a) to social cognitive functioning and empathy , ,  and possibly b) to schizophrenia risk and psychopathology –. Of note, frequencies of both OXTR polymorphisms did not differ between schizophrenic patients and controls in this small sample, thus partially contradicting the findings of . While the negative finding with respect to OXTR rs53576 might be attributed to lower statistical power, OXTR rs2254298 was neither targeted in previous studies of schizophrenic individuals , ,  nor identified as associated with the disease in a large Arab-Israeli pedigree study . For this reason, no final statement can be made about a possible contribution of OXTR rs2254298 polymorphisms to schizophrenia vulnerability so far.
Regarding a broader spectrum of disorders of social cognition, preliminary evidence points to an involvement of OXTR rs2254298, whose A-allele was considered a risk for autism spectrum disorder in Chinese Han families  and in a Japanese case-control study . Interestingly, studies in European and Israeli samples rather identified the rs2254298 G-allele as the risk variant ,  though three family-based studies did not report significant direct associations of SNP rs2254298 with autism , , . Of note, IRI results in patients with Asperger syndrome rather suggest difficulties at ‘perspective taking’ and the inference of epistemological mental states and not primarily involve trait interpersonal warmth and sympathy ; also for this reason our finding cannot be held indicative of a shared vulnerability between the two disease entities. In contrast, it can be speculated that OXTR polymorphisms might differentially modulate behavioral domains in various disorders in interaction with additional specific pathogenetic factors, genetic variants or medication. This might also explain why the empathy-related phenotype in our study was differentially expressed across genotypes in both experimental groups.
Notably, OXTR rs22454298 showed an association only with the IRI ‘empathic concern’ subscale and not with cognitive empathy (IRI ‘perspective taking’) or self-centered aversive arousal in socio-emotional contexts (IRI ‘personal distress’) that both differed significantly between schizophrenic patients and controls. The impact of OXTR polymorphisms on prosocial attitudes in schizophrenia extends reports of an influence of peripheral OXT levels on prosocial symptom scores , emotion recognition , , , social cognition  and trust  in schizophrenia. In partial contrast to our result, recent evidence from a sample of healthy Chinese individuals indicated an association of OXTR rs2254298 with scores of cognitive empathy, but not with the emotional subscales of the IRI - similar to our study, no associations were detected for rs53576 . However, studies cannot easily be compared due to their different ethnic and cultural backgrounds, and discrepancies between Caucasian and Asian samples as for rs2254298 were reported by several authors , , . Investigating OXTR SNP rs53576, Rodrigues et al.  used a composite measure of all other-oriented, cognitive and emotional IRI scales and observed significantly higher values in healthy GG-carriers. Also Krueger et al.  reported higher IRI dispositional empathy and interpersonal trust in 108 healthy men carrying rs53576(GG). Using the same questionnaire, our result substantiates a possible influence of OXTR rs2254298(A>GG), but not OXTR rs53576, on emotional empathy also in schizophrenia.
Although evidence is still conflicting with regard to directionality –, the association of OXTR rs2254298(A>GG) with ‘empathic concern’ is consistent with studies of other patient populations indicating respective links with measures of emotional vulnerability , . Also, the OXTR rs2254298 GG-genotype seemed to be protective with respect to depressive and anxious symptoms in adolescent girls whose mothers had suffered from depression . In contrast, Feldman et al.  reported that parents homozygous for the rs2254298 GG-genotype had lower plasma OXT compared with A allele carriers, and the frequency of parental touch correlated positively with plasma OXT. Recent genetic imaging studies reported an association of OXTR rs2254298(A) with larger bilateral amygdala volumes in healthy Japanese  and healthy female adolescents . Tost et al.  detected a significant decrease in hypothalamus - but not amygdala - gray matter by voxel-based morphometry, a deficient deactivation of the dACG during emotion processing in Caucasian rs2254298 A-carriers, and a relative decoupling of hypothalamus functional connectivity from dACG and amygdala in male A-allele carriers. While ethnical and methodological aspects of these findings are still discussed , results do not contradict a putative link between OXTR rs2254298(A) and a relatively higher emotional reactivity as seen in our study. In schizophrenia, oxytocinergic input may interact with structural ,  and functional abnormalities of the amygdala  and its interconnections with dopaminergic structures and prefrontal cortex - and thus contribute to aberrant emotional salience attribution and alterations of social reward circuitry. Variations in the OXT system may therefore partly explain psychotic core symptoms together with specific socio-emotional deficits in schizophrenia , .
The fact that OXTR rs2254298 specifically impacted other-oriented feelings, but not self-oriented distress, does at first glance not comply with evidence regarding the mitigating role of OXT in emotion regulation per se through its effect on HPA activation . However, it can be hypothesized that the ability to form social bonds and to interpersonally exchange support represents a focal point for OXT-mediated stress regulation. For instance, though previous research confirmed lower stress reactivity in healthy OXTR rs53576(GG) individuals compared to A-allele carriers , other studies administrating OXT during stressful experimental situations suggested an interaction between OXT-mediated stress reduction and the presence of social support . This effect was found to be more prominent in individuals with the rs53576(GG) genotype . Moreover, OXT administration in females in a crucial interpersonal situation - namely during the exposure to infant laughter and crying - increased functional connectivity between the amygdala and neural networks subserving emotion regulation, thus probably reducing negative emotional arousal and aversion , .
Schizophrenic patients carrying an A-allele of OXTR rs2254298 showed significantly higher scores of PANSS general psychopathology, but not of positive or negative symptoms. Although the group of A-carriers comprised comparably more males, patients showed higher scores of ‘empathic concern’. Linear regression analysis identified not gender, but OXTR rs2254298(A), late age of onset of schizophrenia, low PANSS negative, and high PANSS general psychopathology scores as predictors of high self-rated ‘empathic concern’. OXTR rs2254298(A) significantly predicted PANSS general scores. Although mediation analysis in our sample did not confirm significant indirect effects, OXTR rs2254298 A-carriers might represent the more “affective” pole of our schizophrenia sample, with PANSS general scores reflecting the predominance of affective, anxious and psychomotor symptoms. This explanation might be in accord with reports of OXTR rs2254298 impacting the risk for affective disorders –. On the other hand, no significant impact of OXTR polymorphisms was detectable on schizophrenic core symptoms measured with the PANSS positive and negative subscales. While this also could be attributed to insufficient statistical power, results stand in partial contrast to the positive accounts of a therapeutic OXT administration on schizophrenic core - in particular, positive - symptoms , , . Our results might support the view that the oxytocinergic system exerts its effects on schizophrenic psychopathology by impacting lower-level dispositions, such as anxiety, social motivation and perceptual selectivity ,  and not by a selective influence on social cognition and related core symptoms like delusions or ideas of reference . Moreover, future research might elucidate the functional interplay of OXTR polymorphisms and the short-term regulation of peripheral and central OXT levels during socio-emotional processing and its importance for social dysfunction .
Several limitations of the study should be noted. OXTR SNPs were selected on the basis of previous publications. As their functional significance including the existence of influential loci in linkage disequilibrium, as well as regulation and physiology of the cerebral OXT receptor are still not known, genetic associations must not suggest causality. As large effects of genetic variations cannot be expected in complex phenotypes, the limited number of SNPs restricts the validity of our result, while important confounding mechanisms like epistatic factors, polymorphisms of other candidate genes, epigenetic regulation and gene-environment interactions , ,  had to be ignored. Low case numbers prevented a detailed comparison of male and female subsamples, although earlier research indicates pronounced sexual dimorphisms in the OXT system , , , ,  and its genetic variations , , . Also, peripheral OXT levels were not measured, which could have strengthened our result, as preliminary evidence points to a complex relationship of genetic markers, OXT plasma and CSF levels as well as socio-emotional behaviors , .
Also the categorical approach to schizophrenia does not give consideration to this highly heterogeneous disease entity . Ratings of empathy, psychopathology and also peripheral or central OXT levels might be confounded by medication , , , and a dysfunctional interplay of OXT with neurotransmitters like dopamine ,  or serotonin  may disturb feedback regulation between OXT secretion and social context  and prevent the detection of subtle effects of OXTR genetic polymorphisms on behavioral measures.
Finally, we used a single self-rating instrument, although of proven validity in schizophrenia , to assess empathic dimensions. Our results therefore have to be regarded with caution because of their preliminary nature. In conclusion, we give tentative evidence on the involvement of OXTR genetic variants in empathic functioning in schizophrenia. With respect to the high clinical relevance of social cognition in this disorder  and the possible role of OXT as a new pharmacological agent  we suggest that an independent substantiation of our results is warranted.
MANCOVA of 3 IRI scores in schizophrenia patients (SZ, n = 145) and healthy controls (HC, n = 145); factors: OXTR rs2254298 (GG vs. A carriers), gender and diagnosis, covariate: verbal IQ and educational years.
Conceived and designed the experiments: CM JG DJM. Performed the experiments: CM EMB AL DR. Analyzed the data: CM EMB DJM AL. Contributed reagents/materials/analysis tools: DR. Wrote the paper: CM EMB JG DJM AL.
- 1. Ochsner KN (2008) The social-emotional processing stream: five core constructs and their translational potential for schizophrenia and beyond. Biol Psychiatry 64: 48–61. doi: 10.1016/j.biopsych.2008.04.024
- 2. Brüne M, Abdel-Hamid M, Lehmkämper C, Sonntag C (2007) Mental state attribution, neurocognitive functioning, and psychopathology: what predicts poor social competence in schizophrenia best? Schizophr Res 92: 151–159. doi: 10.1016/j.schres.2007.01.006
- 3. Smith MJ, Horan WP, Karpouzian TM, Abram SV, Cobia DJ, et al. (2012) Self-reported empathy deficits are uniquely associated with poor functioning in schizophrenia. Schizophr Res 137(1–3): 196–202. doi: 10.1016/j.schres.2012.01.012
- 4. Bora E, Yücel M, Pantelis C (2009) Theory of mind impairment: a distinct trait-marker for schizophrenia spectrum disorders and bipolar disorder? Acta Psychiatr Scand 120: 253–264. doi: 10.1111/j.1600-0447.2009.01414.x
- 5. Brüne M (2005) “Theory of mind” in schizophrenia: a review of the literature. Schizophr Bull 31: 21–42. doi: 10.1093/schbul/sbi002
- 6. Sprong M, Schothorst P, Vos E, Hox J, van Engeland H (2007) Theory of mind in schizophrenia: meta-analysis. Br J Psychiatry 191: 5–13. doi: 10.1192/bjp.bp.107.035899
- 7. Montag C, Dziobek I, Richter IS, Neuhaus K, Lehmann A, et al. (2011) Different aspects of theory of mind in paranoid schizophrenia: Evidence from a video-based assessment. Psychiatry Res 186(2–3): 203–209. doi: 10.1016/j.psychres.2010.09.006
- 8. Cohen AS, Minor KS (2010) Emotional experience in patients with schizophrenia revisited: meta-analysis of laboratory studies. Schizophr Bull 36: 143–150. doi: 10.1093/schbul/sbn061
- 9. Chan RC, Li H, Cheung EF, Gong QY (2010) Impaired facial emotion perception in schizophrenia: a meta-analysis. Psychiatry Res 178: 381–390. doi: 10.1016/j.psychres.2009.03.035
- 10. Derntl B, Finkelmeyer A, Toygar TK, Hülsmann A, Schneider F, et al. (2009) Generalized deficit in all core components of empathy in schizophrenia. Schizophr Res 108: 197–206. doi: 10.1016/j.schres.2008.11.009
- 11. Achim AM, Ouellet R, Roy MA, Jackson PL (2011) Assessment of empathy in first-episode psychosis and meta-analytic comparison with previous studies in schizophrenia. Psychiatry Res 190: 3–8. doi: 10.1016/j.psychres.2010.10.030
- 12. Neumann ID (2008) Brain oxytocin: a key regulator of emotional and social behaviours in both females and males. J Neuroendocrinol 20: 858–865. doi: 10.1111/j.1365-2826.2008.01726.x
- 13. Lim MM, Young LJ (2006) Neuropeptidergic regulation of affiliative behavior and social bonding in animals. Horm Behav 50: 506–517. doi: 10.1016/j.yhbeh.2006.11.003
- 14. Bartz JA, Hollander E (2006) The neuroscience of affiliation: forging links between basic and clinical research on neuropeptides and social behavior. Horm Behav 50: 518–528. doi: 10.1016/j.yhbeh.2006.06.018
- 15. Heinrichs M, Domes G (2008) Neuropeptides and social behaviour: effects of oxytocin and vasopressin in humans. Prog Brain Res 170: 337–350. doi: 10.1016/s0079-6123(08)00428-7
- 16. Gimpl G, Fahrenholz F (2001) The oxytocin receptor system: structure, function, and regulation. Physiol Rev 81: 629–683.
- 17. Landgraf R, Neumann ID (2004) Vasopressin and oxytocin release within the brain: a dynamic concept of multiple and variable modes of neuropeptide communication. Front Neuroendocrinol 25: 150–176. doi: 10.1016/j.yfrne.2004.05.001
- 18. Huber D, Veinante P, Stoop R (2005) Vasopressin and oxytocin excite distinct neuronal populations in the central amygdala. Science 308: 245–248. doi: 10.1126/science.1105636
- 19. Veenema AH, Neumann ID (2008) Central vasopressin and oxytocin release: regulation of complex social behaviours. Prog Brain Res 170: 261–276. doi: 10.1016/s0079-6123(08)00422-6
- 20. Ross HE, Cole CD, Smith Y, Neumann ID, Landgraf R, et al. (2009) Characterization of the oxytocin system regulating affiliative behavior in female prairie voles. Neuroscience 162: 892–903. doi: 10.1016/j.neuroscience.2009.05.055
- 21. Knobloch HS, Charlet A, Hoffmann LC, Eliava M, Khrulev S, et al. (2012) Evoked axonal oxytocin release in the central amygdala attenuates fear response. Neuron 73: 553–566. doi: 10.1016/j.neuron.2011.11.030
- 22. Donaldson ZR, Young LJ (2008) Oxytocin, vasopressin, and the neurogenetics of sociality. Science 322: 900–904. doi: 10.1126/science.1158668
- 23. Ferguson JN, Aldag JM, Insel TR, Young LJ (2001) Oxytocin in the medial amygdala is essential for social recognition in the mouse. J Neurosci 21: 8278–8285.
- 24. Bale TL, Davis AM, Auger AP, Dorsa DM, McCarthy MM (2001) CNS region-specific oxytocin receptor expression: importance in regulation of anxiety and sex behavior. J Neurosci 21: 2546–2552.
- 25. Campbell P, Ophir AG, Phelps SM (2009) Central vasopressin and oxytocin receptor distributions in two species of singing mice. J Comp Neurol 516: 321–333. doi: 10.1002/cne.22116
- 26. Kéri S, Benedek G (2009) Oxytocin enhances the perception of biological motion in humans. Cogn Affect Behav Neurosci 9: 237–241. doi: 10.3758/cabn.9.3.237
- 27. Domes G, Heinrichs M, Michel A, Berger C, Herpertz SC (2007) Oxytocin improves “mind-reading” in humans. Biol Psychiatry 61: 731–733. doi: 10.1016/j.biopsych.2006.07.015
- 28. Bartz JA, Zaki J, Bolger N, Hollander E, Ludwig NN, et al. (2010) Oxytocin selectively improves empathic accuracy. Psychol Sci 21: 1426–1428. doi: 10.1177/0956797610383439
- 29. Savaskan E, Ehrhardt R, Schulz A, Walter M, Schachinger H (2008) Post-learning intranasal oxytocin modulates human memory for facial identity. Psychoneuroendocrinology 33: 368–374. doi: 10.1016/j.psyneuen.2007.12.004
- 30. Guastella AJ, Mitchell PB, Mathews F (2008) Oxytocin enhances the encoding of positive social memories in humans. Biol Psychiatry 64: 256–258. doi: 10.1016/j.biopsych.2008.02.008
- 31. Bartz JA, Zaki J, Ochsner KN, Bolger N, Kolevzon A, et al. (2010) Effects of oxytocin on recollections of maternal care and closeness. Proc Natl Acad Sci U S A 107: 21371–21375. doi: 10.1073/pnas.1012669107
- 32. Zak PJ, Stanton AA, Ahmadi S (2007) Oxytocin increases generosity in humans. PLoS One 2: e1128. 10.1371/journal.pone.0001128 [doi].
- 33. Macdonald K, Macdonald TM (2010) The peptide that binds: a systematic review of oxytocin and its prosocial effects in humans. Harv Rev Psychiatry 18: 1–21. doi: 10.3109/10673220903523615
- 34. Striepens N, Kendrick KM, Maier W, Hurlemann R (2011) Prosocial effects of oxytocin and clinical evidence for its therapeutic potential. Front Neuroendocrinol 32: 426–450. doi: 10.1016/j.yfrne.2011.07.001
- 35. Buchheim A, Heinrichs M, George C, Pokorny D, Koops E, et al. (2009) Oxytocin enhances the experience of attachment security. Psychoneuroendocrinology 34: 1417–1422. doi: 10.1016/j.psyneuen.2009.04.002
- 36. Kéri S, Kiss I (2011) Oxytocin response in a trust game and habituation of arousal. Physiol Behav 102: 221–224. doi: 10.1016/j.physbeh.2010.11.011
- 37. Neumann ID (2002) Involvement of the brain oxytocin system in stress coping: interactions with the hypothalamo-pituitary-adrenal axis. Prog Brain Res 139: 147–162. doi: 10.1016/s0079-6123(02)39014-9
- 38. Heinrichs M, Baumgartner T, Kirschbaum C, Ehlert U (2003) Social support and oxytocin interact to suppress cortisol and subjective responses to psychosocial stress. Biol Psychiatry 54: 1389–1398. doi: 10.1016/s0006-3223(03)00465-7
- 39. Kirsch P, Esslinger C, Chen Q, Mier D, Lis S, et al. (2005) Oxytocin modulates neural circuitry for social cognition and fear in humans. J Neurosci 25: 11489–11493. doi: 10.1523/jneurosci.3984-05.2005
- 40. Domes G, Heinrichs M, Glascher J, Buchel C, Braus DF, et al. (2007) Oxytocin attenuates amygdala responses to emotional faces regardless of valence. Biol Psychiatry 62: 1187–1190. doi: 10.1016/j.biopsych.2007.03.025
- 41. Baumgartner T, Heinrichs M, Vonlanthen A, Fischbacher U, Fehr E (2008) Oxytocin shapes the neural circuitry of trust and trust adaptation in humans. Neuron 58: 639–650. doi: 10.1016/j.neuron.2008.04.009
- 42. Petrovic P, Kalisch R, Singer T, Dolan RJ (2008) Oxytocin attenuates affective evaluations of conditioned faces and amygdala activity. J Neurosci 28: 6607–6615. doi: 10.1523/jneurosci.4572-07.2008
- 43. Baskerville TA, Douglas AJ (2010) Dopamine and oxytocin interactions underlying behaviors: potential contributions to behavioral disorders. CNS Neurosci Ther 16: e92–123. doi: 10.1111/j.1755-5949.2010.00154.x
- 44. Rosenfeld AJ, Lieberman JA, Jarskog LF (2011) Oxytocin, Dopamine, and the Amygdala: A Neurofunctional Model of Social Cognitive Deficits in Schizophrenia. Schizophr Bull 37(5): 1077–1087. doi: 10.1093/schbul/sbq015
- 45. Skuse DH, Gallagher L (2011) Genetic influences on social cognition. Pediatr Res 69: 85R–91R. doi: 10.1203/pdr.0b013e318212f562
- 46. Skuse DH, Gallagher L (2009) Dopaminergic-neuropeptide interactions in the social brain. Trends Cogn Sci 13: 27–35. doi: 10.1016/j.tics.2008.09.007
- 47. Lee PR, Brady DL, Shapiro RA, Dorsa DM, Koenig JI (2007) Prenatal stress generates deficits in rat social behavior: Reversal by oxytocin. Brain Res 1156: 152–167. doi: 10.1016/j.brainres.2007.04.042
- 48. Rubin LH, Carter CS, Drogos L, Pournajafi-Nazarloo H, Sweeney JA, et al. (2010) Peripheral oxytocin is associated with reduced symptom severity in schizophrenia. Schizophr Res 124: 13–21. doi: 10.1016/j.schres.2010.09.014
- 49. Rubin LH, Carter CS, Drogos L, Jamadar R, Pournajafi-Nazarloo H, et al. (2011) Sex-specific associations between peripheral oxytocin and emotion perception in schizophrenia. Schizophr Res 130: 266–270. doi: 10.1016/j.schres.2011.06.002
- 50. Sasayama D, Hattori K, Teraishi T, Hori H, Ota M, et al. (2012) Negative correlation between cerebrospinal fluid oxytocin levels and negative symptoms of male patients with schizophrenia. Schizophr Res 139: 201–206. doi: 10.1016/j.schres.2012.06.016
- 51. Feifel D, Macdonald K, Nguyen A, Cobb P, Warlan H, et al. (2010) Adjunctive intranasal oxytocin reduces symptoms in schizophrenia patients. Biol Psychiatry 68: 678–680. doi: 10.1016/j.biopsych.2010.04.039
- 52. Pedersen CA, Gibson CM, Rau SW, Salimi K, Smedley KL, et al. (2011) Intranasal oxytocin reduces psychotic symptoms and improves Theory of Mind and social perception in schizophrenia. Schizophr Res 132: 50–53. doi: 10.1016/j.schres.2011.07.027
- 53. Bujanow W (1974) Letter: Is oxytocin an anti-schizophrenic hormone? Can Psychiatr Assoc J 19: 323.
- 54. Averbeck BB, Bobin T, Evans S, Shergill SS (2011) Emotion recognition and oxytocin in patients with schizophrenia. Psychol Med 1–8.
- 55. Feifel D, Macdonald K, Cobb P, Minassian A (2012) Adjunctive intranasal oxytocin improves verbal memory in people with schizophrenia. Schizophr Res 139: 207–210. doi: 10.1016/j.schres.2012.05.018
- 56. Uvnäs-Moberg K, Alster P, Svensson TH (1992) Amperozide and clozapine but not haloperidol or raclopride increase the secretion of oxytocin in rats. Psychopharmacology (Berl) 109: 473–476. doi: 10.1007/bf02247726
- 57. Kiss A, Bundzikova J, Pirnik Z, Mikkelsen JD (2010) Different antipsychotics elicit different effects on magnocellular oxytocinergic and vasopressinergic neurons as revealed by Fos immunohistochemistry. J Neurosci Res 88: 677–685. doi: 10.1002/jnr.22226
- 58. Lee PR, Brady DL, Shapiro RA, Dorsa DM, Koenig JI (2005) Social interaction deficits caused by chronic phencyclidine administration are reversed by oxytocin. Neuropsychopharmacology 30: 1883–1894. doi: 10.1038/sj.npp.1300722
- 59. Feifel D, Reza T (1999) Oxytocin modulates psychotomimetic-induced deficits in sensorimotor gating. Psychopharmacology (Berl) 141: 93–98. doi: 10.1007/s002130050811
- 60. Wu S, Jia M, Ruan Y, Liu J, Guo Y, et al. (2005) Positive association of the oxytocin receptor gene (OXTR) with autism in the Chinese Han population. Biol Psychiatry 58: 74–77. doi: 10.1016/j.biopsych.2005.03.013
- 61. Gregory SG, Connelly JJ, Towers AJ, Johnson J, Biscocho D, et al. (2009) Genomic and epigenetic evidence for oxytocin receptor deficiency in autism. BMC Med 7: 62. doi: 10.1186/1741-7015-7-62
- 62. Jacob S, Brune CW, Carter CS, Leventhal BL, Lord C, et al. (2007) Association of the oxytocin receptor gene (OXTR) in Caucasian children and adolescents with autism. Neurosci Lett 417: 6–9. doi: 10.1016/j.neulet.2007.02.001
- 63. Liu X, Kawamura Y, Shimada T, Otowa T, Koishi S, et al. (2010) Association of the oxytocin receptor (OXTR) gene polymorphisms with autism spectrum disorder (ASD) in the Japanese population. J Hum Genet 55: 137–141. doi: 10.1038/jhg.2009.140
- 64. Ylisaukko-oja T, Alarcon M, Cantor RM, Auranen M, Vanhala R, et al. (2006) Search for autism loci by combined analysis of Autism Genetic Resource Exchange and Finnish families. Ann Neurol 59: 145–155. doi: 10.1002/ana.20722
- 65. Yrigollen CM, Han SS, Kochetkova A, Babitz T, Chang JT, et al. (2008) Genes controlling affiliative behavior as candidate genes for autism. Biol Psychiatry 63: 911–916. doi: 10.1016/j.biopsych.2007.11.015
- 66. Tansey KE, Brookes KJ, Hill MJ, Cochrane LE, Gill M, et al. (2010) Oxytocin receptor (OXTR) does not play a major role in the aetiology of autism: genetic and molecular studies. Neurosci Lett 474: 163–167. doi: 10.1016/j.neulet.2010.03.035
- 67. Wermter AK, Kamp-Becker I, Hesse P, Schulte-Korne G, Strauch K, et al. (2010) Evidence for the involvement of genetic variation in the oxytocin receptor gene (OXTR) in the etiology of autistic disorders on high-functioning level. Am J Med Genet B Neuropsychiatr Genet 153B: 629–639. doi: 10.1002/ajmg.b.31032
- 68. Campbell DB, Datta D, Jones ST, Batey LE, Sutcliffe JS, et al. (2011) Association of oxytocin receptor (OXTR) gene variants with multiple phenotype domains of autism spectrum disorder. J Neurodev Disord 3(2): 101–112. doi: 10.1007/s11689-010-9071-2
- 69. Souza RP, de L, V, Meltzer HY, Lieberman JA, Kennedy JL (2010) Schizophrenia severity and clozapine treatment outcome association with oxytocinergic genes. Int J Neuropsychopharmacol 13: 793–798. doi: 10.1017/s1461145710000167
- 70. Souza RP, Ismail P, Meltzer HY, Kennedy JL (2010) Variants in the oxytocin gene and risk for schizophrenia. Schizophr Res 121: 279–280. doi: 10.1016/j.schres.2010.04.019
- 71. Teltsh O, Kanyas-Sarner K, Rigbi A, Greenbaum L, et al.. (2011) Oxytocin and vasopressin genes are significantly associated with schizophrenia in a large Arab-Israeli pedigree. Int J Neuropsychopharmacol 1–11.
- 72. Montag C, Brockmann EM, Bayerl M, Rujescu D, Muller DJ, et al.. (2012) Oxytocin and oxytocin receptor gene polymorphisms and risk for schizophrenia: A case-control study. World J Biol Psychiatry. 10.3109/15622975.2012.677547 [doi].
- 73. Rodrigues SM, Saslow LR, Garcia N, John OP, Keltner D (2009) Oxytocin receptor genetic variation relates to empathy and stress reactivity in humans. Proc Natl Acad Sci U S A 106: 21437–21441. doi: 10.1073/pnas.0909579106
- 74. Chen FS, Kumsta R, von Dawans B, Monakhov M, Ebstein RP, et al. (2011) Common oxytocin receptor gene (OXTR) polymorphism and social support interact to reduce stress in humans. Proc Natl Acad Sci U S A 108: 19937–19942. doi: 10.1073/pnas.1113079108
- 75. Norman GJ, Hawkley L, Luhmann M, Ball AB, Cole SW, et al.. (2012) Variation in the oxytocin receptor gene influences neurocardiac reactivity to social stress and HPA function: a population based study. Horm Behav 61: 134–139. S0018–506X(11)00271–6 [pii];10.1016/j.yhbeh.2011.11.006 [doi].
- 76. Kogan A, Saslow LR, Impett EA, Oveis C, Keltner D, et al. (2011) Thin-slicing study of the oxytocin receptor (OXTR) gene and the evaluation and expression of the prosocial disposition. Proc Natl Acad Sci U S A 108: 19189–19192. doi: 10.1073/pnas.1112658108
- 77. Kim HS, Sherman DK, Sasaki JY, Xu J, Chu TQ, et al. (2010) Culture, distress, and oxytocin receptor polymorphism (OXTR) interact to influence emotional support seeking. Proc Natl Acad Sci U S A 107: 15717–15721. doi: 10.1073/pnas.1010830107
- 78. Krueger F, Parasuraman R, Iyengar V, Thornburg M, Weel J, et al.. (2012) Oxytocin receptor genetic variation promotes human trust behavior. Front Hum Neurosci 6: 4. 10.3389/fnhum.2012.00004 [doi].
- 79. Wu N, Li Z, Su Y (2012) The association between oxytocin receptor gene polymorphism (OXTR) and trait empathy. J Affect Disord. S0165–0327(12)00016-X [pii];10.1016/j.jad.2012.01.009 [doi].
- 80. Chen FS, Barth ME, Johnson SL, Gotlib IH, Johnson SC (2011) Oxytocin Receptor (OXTR) Polymorphisms and Attachment in Human Infants. Frontiers in Psychology 2: 200. doi: 10.3389/fpsyg.2011.00200
- 81. Feldman R, Zagoory-Sharon O, Weisman O, Schneiderman I, Gordon I, et al.. (2012) Sensitive Parenting is Associated with Plasma Oxytocin and Polymorphisms in the OXTR and CD38 Genes. Biol Psychiatry. S0006–3223(12)00003–0 [pii];10.1016/j.biopsych.2011.12.025 [doi].
- 82. Costa B, Pini S, Gabelloni P, Abelli M, Lari L, et al. (2009) Oxytocin receptor polymorphisms and adult attachment style in patients with depression. Psychoneuroendocrinology 34: 1506–1514. doi: 10.1016/j.psyneuen.2009.05.006
- 83. Bakermans-Kranenburg MJ, van Ijzendoorn MH (2008) Oxytocin receptor (OXTR) and serotonin transporter (5-HTT) genes associated with observed parenting. Soc Cogn Affect Neurosci 3: 128–134. doi: 10.1093/scan/nsn004
- 84. Lerer E, Levi S, Salomon S, Darvasi A, Yirmiya N, et al. (2008) Association between the oxytocin receptor (OXTR) gene and autism: relationship to Vineland Adaptive Behavior Scales and cognition. Mol Psychiatry 13: 980–988. doi: 10.1038/sj.mp.4002087
- 85. Inoue H, Yamasue H, Tochigi M, Abe O, Liu X, et al. (2010) Association between the oxytocin receptor gene and amygdalar volume in healthy adults. Biol Psychiatry 68: 1066–1072. doi: 10.1016/j.biopsych.2010.07.019
- 86. Furman DJ, Chen MC, Gotlib IH (2011) Variant in oxytocin receptor gene is associated with amygdala volume. Psychoneuroendocrinology 36: 891–897. doi: 10.1016/j.psyneuen.2010.12.004
- 87. Tost H, Kolachana B, Verchinski BA, Bilek E, Goldman AL, et al. (2011) Neurogenetic effects of OXTR rs2254298 in the extended limbic system of healthy Caucasian adults. Biol Psychiatry 70: e37–e39. doi: 10.1016/j.biopsych.2011.06.034
- 88. Tost H, Kolachana B, Hakimi S, Lemaitre H, Verchinski BA, et al. (2010) A common allele in the oxytocin receptor gene (OXTR) impacts prosocial temperament and human hypothalamic-limbic structure and function. Proc Natl Acad Sci U S A 107: 13936–13941. doi: 10.1073/pnas.1003296107
- 89. Davis MH (1983) Measuring Individual Differences in Empathy: Evidence for a Multidimensional Approach. Journal of Personality and Social Psychology 44: 113–126. doi: 10.1037//0022-3522.214.171.124
- 90. Helmchen H, Lauter H (1995) [Ethical problems in biomedical research with cognitively impaired elderly patients]. Nervenarzt 66: 231–238.
- 91. Wittchen HU, Fydrich T, Zaudig M (1997) SKID-I und SCID-II. Strukturiertes Klinisches Interview für DSM-IV. Göttingen, Germany : Hogrefe, Verlag für Psychologie.
- 92. Kay SR, Fiszbein A, Opler LA (1987) The positive and negative syndrome scale (PANSS) for schizophrenia. Schizophr Bull 13: 261–276. doi: 10.1093/schbul/13.2.261
- 93. Sheehan DV, Lecrubier Y, Sheehan KH, Amorim P, Janavs J, et al. (1998) The Mini-International Neuropsychiatric Interview (M.I.N.I.): the development and validation of a structured diagnostic psychiatric interview for DSM-IV and ICD-10. J Clin Psychiatry 59 Suppl 2022–33. doi: 10.1016/s0924-9338(97)83296-8
- 94. Paulus C. (1992) Empathie, Kompetenz und Altruismus. Available: www uni-saarland de/fak5/ezw/abteil/motiv/paper/empathie htm.
- 95. Montag C, Heinz A, Kunz D, Gallinat J (2007) Self-reported empathic abilities in schizophrenia. Schizophr Res 92: 85–89. doi: 10.1016/j.schres.2007.01.024
- 96. Lehrl S, Triebig G, Fischer B (1995) Multiple choice vocabulary test MWT as a valid and short test to estimate premorbid intelligence. Acta Neurol Scand 91: 335–345. doi: 10.1111/j.1600-0404.1995.tb07018.x
- 97. Preacher KJ, Hayes AF (2008) Asymptotic and resampling strategies for assessing and comparing indirect effects in multiple mediator models. Behavior Research Methods 40: 879–891. doi: 10.3758/brm.40.3.879
- 98. Brüne M (2012) Does the oxytocin receptor (OXTR) polymorphism (rs2254298) confer “vulnerability” for psychopathology or “differential susceptibility”? Insights from evolution. BMC Med 10: 38. doi: 10.1186/1741-7015-10-38
- 99. Rogers K, Dziobek I, Hassenstab J, Wolf OT, Convit A (2007) Who cares? Revisiting empathy in Asperger syndrome. J Autism Dev Disord 37: 709–715. doi: 10.1007/s10803-006-0197-8
- 100. Goldman M, Marlow-O’Connor M, Torres I, Carter CS (2008) Diminished plasma oxytocin in schizophrenic patients with neuroendocrine dysfunction and emotional deficits. Schizophr Res 98: 247–255. doi: 10.1016/j.schres.2007.09.019
- 101. Kéri S, Kiss I, Kelemen O (2009) Sharing secrets: oxytocin and trust in schizophrenia. Soc Neurosci 4: 287–293. doi: 10.1080/17470910802319710
- 102. Kawamura Y, Liu X, Akiyama T, Shimada T, Otowa T, et al. (2010) The association between oxytocin receptor gene (OXTR) polymorphisms and affective temperaments, as measured by TEMPS-A. J Affect Disord 127: 31–37. doi: 10.1016/j.jad.2010.04.014
- 103. Lucht MJ, Barnow S, Sonnenfeld C, Rosenberger A, Grabe HJ, et al. (2009) Associations between the oxytocin receptor gene (OXTR) and affect, loneliness and intelligence in normal subjects. Prog Neuropsychopharmacol Biol Psychiatry 33: 860–866. doi: 10.1016/j.pnpbp.2009.04.004
- 104. Thompson RJ, Parker KJ, Hallmayer JF, Waugh CE, Gotlib IH (2011) Oxytocin receptor gene polymorphism (rs2254298) interacts with familial risk for psychopathology to predict symptoms of depression and anxiety in adolescent girls. Psychoneuroendocrinology 36: 144–147. doi: 10.1016/j.psyneuen.2010.07.003
- 105. Yamasue H, Suga M, Yahata N, Inoue H, Tochigi M, et al. (2011) Reply to: Neurogenetic effects of OXTR rs2254298 in the extended limbic system of healthy Caucasian adults. Biol Psychiatry 70: e41–e42. doi: 10.1016/j.biopsych.2011.07.021
- 106. Wright IC, Rabe-Hesketh S, Woodruff PW, David AS, Murray RM, et al. (2000) Meta-analysis of regional brain volumes in schizophrenia. Am J Psychiatry 157: 16–25.
- 107. Tomasino B, Bellani M, Perlini C, Rambaldelli G, Cerini R, et al. (2011) Altered microstructure integrity of the amygdala in schizophrenia: a bimodal MRI and DWI study. Psychol Med 41: 301–311. doi: 10.1017/s0033291710000875
- 108. Derntl B, Finkelmeyer A, Voss B, Eickhoff SB, Kellermann T, et al. (2012) Neural correlates of the core facets of empathy in schizophrenia. Schizophr Res 136: 70–81. doi: 10.1016/j.schres.2011.12.018
- 109. Riem MM, van Ijzendoorn MH, Tops M, Boksem MA, Rombouts SA, et al. (2012) No Laughing Matter: Intranasal Oxytocin Administration Changes Functional Brain Connectivity during Exposure to Infant Laughter. Neuropsychopharmacology 37(5): 1257–1266. doi: 10.1038/npp.2011.313
- 110. Riem MM, Bakermans-Kranenburg MJ, Pieper S, Tops M, Boksem MA, et al. (2011) Oxytocin Modulates Amygdala, Insula, and Inferior Frontal Gyrus Responses to Infant Crying: A Randomized Controlled Trial. Biol Psychiatry 70(3): 291–297. doi: 10.1016/j.biopsych.2011.02.006
- 111. Macdonald K, Feifel D (2012) Oxytocin in schizophrenia: a review of evidence for its therapeutic effects. Acta Neuropsychiatr 24: 130–146. doi: 10.1111/j.1601-5215.2011.00634.x
- 112. Churchland PS, Winkielman P (2012) Modulating social behavior with oxytocin: How does it work? What does it mean? Horm Behav 61(3): 392–399. doi: 10.1016/j.yhbeh.2011.12.003
- 113. Bartz JA, Zaki J, Bolger N, Ochsner KN (2011) Social effects of oxytocin in humans: context and person matter. Trends Cogn Sci 15: 301–309. doi: 10.1016/j.tics.2011.05.002
- 114. Frith CD (2004) Schizophrenia and theory of mind. Psychol Med 34: 385–389. doi: 10.1017/s0033291703001326
- 115. Meyer-Lindenberg A, Domes G, Kirsch P, Heinrichs M (2011) Oxytocin and vasopressin in the human brain: social neuropeptides for translational medicine. Nat Rev Neurosci 12: 524–538. doi: 10.1038/nrn3044
- 116. Kimura T, Saji F, Nishimori K, Ogita K, Nakamura H, et al. (2003) Molecular regulation of the oxytocin receptor in peripheral organs. J Mol Endocrinol 30: 109–115. doi: 10.1677/jme.0.0300109
- 117. Carter CS (2007) Sex differences in oxytocin and vasopressin: implications for autism spectrum disorders? Behav Brain Res 176: 170–186. doi: 10.1016/j.bbr.2006.08.025
- 118. Murakami G, Hunter RG, Fontaine C, Ribeiro A, Pfaff D (2011) Relationships among estrogen receptor, oxytocin and vasopressin gene expression and social interaction in male mice. Eur J Neurosci 34: 469–477. doi: 10.1111/j.1460-9568.2011.07761.x
- 119. Goldman MB, Gomes AM, Carter CS, Lee R (2011) Divergent effects of two different doses of intranasal oxytocin on facial affect discrimination in schizophrenic patients with and without polydipsia. Psychopharmacology (Berl) 216(1): 101–110. doi: 10.1007/s00213-011-2193-8