Genetic variation in the vasopressin receptor 1a gene
(AVPR1A) associates with pair-bonding behavior
Hasse Walum*†‡, Lars Westberg†§, Susanne Henningsson§, Jenae M. Neiderhiser¶, David Reiss?, Wilmar Igl*,
Jody M. Ganiban**, Erica L. Spotts††, Nancy L. Pedersen*, Elias Eriksson§, and Paul Lichtenstein*
*Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, S-171 77 Stockholm, Sweden;§Department of Pharmacology,
Institute of Neuroscience and Physiology, University of Gothenburg, Box 431, S 405 30 Gothenburg, Sweden;¶Department of Psychology,
Pennsylvania State University, University Park, PA 16802;?Yale Child Study Center, Yale University, New Haven, CT 06520; **Department
of Psychology, The George Washington University, Building GG 2125 G St NW, Washington, DC 20052; and††Behavioral and Social
Research Program, National Institute on Aging, Bethesda, MD 20892-9205
Edited by Solomon H. Snyder, Johns Hopkins University School of Medicine, Baltimore, MD, and approved July 14, 2008 (received for review March 28, 2008)
Pair-bonding has been suggested to be a critical factor in the
evolutionary development of the social brain. The brain neuropep-
tide arginine vasopressin (AVP) exerts an important influence on
pair-bonding behavior in voles. There is a strong association
between a polymorphic repeat sequence in the 5? flanking region
of the gene (avpr1a) encoding one of the AVP receptor subtypes
(V1aR), and proneness for monogamous behavior in males of this
species. It is not yet known whether similar mechanisms are
important also for human pair-bonding. Here, we report an asso-
ciation between one of the human AVPR1A repeat polymorphisms
(RS3) and traits reflecting pair-bonding behavior in men, including
partner bonding, perceived marital problems, and marital status,
and show that the RS3 genotype of the males also affects marital
quality as perceived by their spouses. These results suggest an
association between a single gene and pair-bonding behavior in
humans, and indicate that the well characterized influence of AVP
on pair-bonding in voles may be of relevance also for humans.
monogamy ? neuropeptide ? polymorphism ? social behavior
neuropeptide arginine vasopressin (AVP), acting through the re-
ceptor subtype V1aR, plays a key role in the regulation of pair-
bonding behavior in male rodents, as revealed by a series of elegant
studies on closely related vole species, i.e., montane voles (Microtus
montanus), meadow voles (Microtus pennsylvanicus), and prairie
voles (Microtus ochrogaster) (2). In prairie voles, which in contrast
social, pair-bond formation and related behaviors are facilitated by
AVP and prevented by a V1aR antagonist (3). Supporting the
theory that the striking difference in pair-bonding between mo-
nogamous and nonmonogamous voles is related to the influence of
AVP on this behavior, the neuroanatomical distribution of V1aR
with sexual and social fidelity among prairie voles (5). Moreover,
partner preference is enhanced in the nonmonogamous meadow
vole when the V1aR density is increased in relevant brain areas by
using viral vector gene transfer (6). Although there are no major
differences in the coding sequence of the gene encoding V1aR
(avpr1a) between prairie, montane or meadow voles, the former
species displays a 428-base pair sequence in the 5? flanking region
that is not found in the latter two species. When the avpr1a of the
inserted into the nonmonogamous species mouse (7), more pro-
nounced social behavior, similar to that displayed by prairie voles,
is generated. Furthermore, variation in the 5? flanking region of
rimate social organization is often characterized by bonded
relationships, and recent analyses suggest that it may have been
prairie vole avpr1a affects brain expression of the gene and alters
intraspecific variation in partner preference (8).
Human AVPR1A is situated on chromosome 12q14–15 (9).
Whereas there is no sequence in the human AVPR1A 5? flanking
region homologous to the one found in prairie voles, humans do
have three repetitive sequences in this region that are polymor-
phic: A (GT)25dinucleotide repeat, a complex (CT)4-TT-(CT)8-
(GT)24repeat (RS3), and a (GATA)14tetranucleotide repeat
(RS1) (10). Although as yet not consistently replicated, previous
studies have revealed associations between AVPR1A repeat
polymorphisms and autism (11–13), age at first sexual inter-
course (14), and altruism (15), suggesting that these repetitive
sequences may have an impact on human social behavior.
The aim of this study was to investigate whether variability in
the 5? flanking region of AVPR1A affects pair-bonding behavior
in humans as it does in prairie voles. To this end, the three repeat
women from the Twin and Offspring Study in Sweden (TOSS),
comprised of 552 same-sex twin-pairs and their spouses/partners
(16). All subjects were assessed with respect to various indices of
the quality of the marital relationship, including a new scale–the
Partner Bonding Scale (PBS)–which is comprised of items that
correspond to the behavioral patterns observed when measuring
features of pair-bonds among nonhuman primates.
The allele and genotype distributions of the three repeat poly-
morphisms (RS1, RS3, and GT25) were similar to what has been
reported in previous studies (10, 11, 17) and did not deviate from
Hardy–Weinberg equilibrium. After correction for multiple
tests, there was a significant global P value for an association
between the RS3-repeat polymorphism and the outcome of the
PBS for men (P ? 0.01 after a Bonferroni correction of the six
tests), but not for women (Table 1). No associations were found
for the other AVPR1A polymorphisms. When comparing the
mean scores of the PBS for each RS3 allele (Table 2), this value
was found to be significantly lower for men carrying allele 334
than for those not carrying this allele (F1,130? 16.35, P ? 0.0001,
Author contributions: H.W., L.W., S.H., J.M.N., D.R., J.M.G., E.L.S., N.L.P., E.E., and P.L.
designed research; W.I. contributed new reagents/analytic tools; H.W. analyzed data; and
H.W. and L.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Freely available online through the PNAS open access option.
†H.W. and L.W. contributed equally to this work.
‡To whom correspondence should be addressed. E-mail: email@example.com.
This article contains supporting information online at www.pnas.org/cgi/content/full/
© 2008 by The National Academy of Sciences of the USA
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vol. 105 ?
no. 37 ?
d ? 0.27; P ? 0.001 after correction for the 11 tests). In addition,
a dose-dependent effect of the number of 334 alleles on the PBS
score (Table 3) was found, with carriers of two alleles showing
the lowest scores. The size of these effects were d ? 0.27 between
men not carrying any 334 allele and 334 heterozygotes, and d ?
0.38 between men not carrying any 334 allele and 334 homozy-
gotes. After Bonferroni correction, no RS3 allele other than the
The association between the RS3 polymorphism and the
scores of the PBS prompted us to examine to what extent an
influence of this polymorphism on marital quality could be
detected when using other measures than the PBS. To this end,
we first assessed whether carriers of allele 334 reported more
marital problems than men without it, by using an item collected
from a life event questionnaire based on the Social Readjust-
ment Rating Scale (18), asking whether the male subjects had
experienced marital crisis or threat of divorce during the last
year. In line with our assumption, carriers of the RS3 allele 334
responded affirmatively more often to this question (Table 3).
Fifteen percent of the men carrying no 334 allele reported
allele reported marital crisis, suggesting that being homozygous
for the 334 allele doubles the risk of marital crisis compared with
having no 334 allele.
The validity analysis, reported in the Materials and Methods
section, showed that unmarried individuals scored significantly
lower than married subjects on the PBS. Thus, we hypothesized
that men carrying the RS3 allele 334 more often were involved
in a relationship without being married. The allele 334 was
indeed associated with marital status (Table 3); the frequency of
nonmarried men being higher among 334 homozygotes (32%)
than among men with no 334 alleles (17%).
Next we investigated whether the genotype of the men influ-
enced marital quality as perceived by their spouses. For this
purpose, we used the Dyadic Consensus, Dyadic Satisfaction,
Dyadic Cohesion, and Affectional Expression subscales from the
Dyadic Adjustment Scale (DAS) (19), measures frequently used
to evaluate the quality of marital relationships. As hypothesized,
the marital quality, as perceived by the wives, was significantly
associated with the RS3 genotype of their husbands. Women
married to men with one or two 334 alleles scored significantly
lower on the Affection Expression, Dyadic Consensus, and
Dyadic Cohesion subscales than did women married to men
without the 334 allele (Table 4), and effect sizes ranged from d ?
0.14–0.20. However, the difference between carriers of one or
two 334 alleles that was observed when analyzing the outcome
of the PBS for the men was not found for the rating conducted
estimates (?) was obtained; suggesting that the behaviors as-
sessed by the PBS mediate the association of the 334 allele with
the wives’ reported quality of the marital relationship.
The results from the current study suggest an association be-
tween a AVPR1A polymorphism and human pair-bonding be-
havior possibly analogous to that reported for voles (8). One of
the most common RS3 alleles, the allele 334, was associated with
perceived partner bonding in men as assessed by using the PBS.
This association could be detected also by assessing marital
problems and marital status in men, and the perception of the
quality of the marital relationship expressed by their spouses.
That an association between the studied gene and items reflect-
that the influence of vasopressin on social behavior is more
prominent in male than in female voles (20).
Although the functional importance of the RS3 polymorphism
of the AVPR1A remains to be clarified, an association between
the length of the RS3 repeat and the amount of hippocampal
mRNA in human postmortem tissue has been reported (15).
Moreover, a recent study in healthy subjects suggests that the 334
allele is associated with increased activation of amygdala, a brain
region known to be of importance for pair-bonding behavior
(17). The conclusion of our study (that the 334 allele of the RS3
polymorphism influences brain function) is well in line with
The possible influence of AVP on social interactions has led
researchers to suggest an involvement of this transmitter in
conditions characterized by social deficits, for example, autism
and autism-related conditions. This theory has gained support
from studies assessing the possible association between AVPR1A
and risk for autism (11–13) and other traits related to interper-
sonal relationships (15). Although it is difficult to compare the
results of these studies to those of our study, it is of interest to
note that one of these studies suggests the 334 allele to be
over-transmitted to subjects with autism (11). The observation
that a gene variant, which according to our data, is negatively
associated with the ability to interact within a relationship, may
enhance the risk for a condition characterized by impaired social
impairments of social relatedness and communication is obvi-
The effect size (d) for the influence of the studied allele on
PBS scores when comparing men who carry one or two 334
alleles with those who do not carry any was 0.27. This is
comparable with what has been reported in large metaanalyses
of the association between a DRD4 polymorphism and the
a serotonin transporter polymorphism and neuroticism (d ?
0.23) (20), despite the fact that the outcome of the PBS, unlike
Table 2. Association between different RS3 alleles and the
Partner Bonding Scale in men
Analyses were performed by comparing individuals carrying one or two of
an allele with individuals not carrying this allele. Freq, Frequency, denoting
number of individuals carrying one or two of the given allele. Mean, Mean
Table 1. Association between the different microsatellite
polymorphisms in the AVPR1A 5? flanking region and the
Partner Bonding Scale
Only genotypes for which n ? 10 were included in the analyses.
www.pnas.org?cgi?doi?10.1073?pnas.0803081105Walum et al.
novelty seeking and neuroticism to some extent is influenced not
only by the informant but also by his/her partner.
It is notable that an association was found between the RS3
repeat of the AVPR1A and indices of pair-bonding behavior in
a cohort in which all subjects had been married or cohabiting for
at least five years. Tentatively, such an association would be even
stronger in a population also comprising subjects not involved in
any long-term romantic relationships. It would also be of im-
portance to assess the possible influence of this polymorphism
on measures of pair-bonding that are more objective than
self-report, such as proneness for cohabiting versus living alone,
marriage, and divorce. However, of some interest in this context
is our observation that men that were homozygous for the 334
allele were more likely to be unmarried than other men, despite
the fact that the cohabiting individuals in our sample had been
in a relationship persisting for at least five years and that in the
vast majority of all of these couples, both individuals were
biological parents to a adolescent child, ranging in age from 11-
to 22-years-old. This finding is in line with the observation that
unmarried men displayed lower scores on the PBS (see Materials
and Methods) and may tentatively reflect a lower degree of
commitment in those being unmarried.
The relatively small effect size of the AVPR1A polymorphism
on traits tentatively reflecting pair-bonding in males observed in
this study clearly does not mean that this polymorphism may
serve as a predictor of human pair-bonding behavior on the
individual level. However, by demonstrating a modest but sig-
nificant influence of this gene on the studied behavior on the
group level, we have provided support for the assumption that
previous studies on the influence of the gene coding for V1aR on
pair-bonding in voles are probably of relevance also for humans.
Materials and Methods
Subjects. The study consisted of 552 twin pairs and their spouses from the
ality, attachment style, and the mental health of all study participants were
collected (16). Participants were mostly middle class and born between 1944
and 1971. Consistent with the population of Sweden, the vast majority were
article by Neiderhiser and coworkers (16). The same-sex twins included in the
study were required to have a relationship of at least five years with their
simplicity, both married and unmarried cohabiting individuals are referred to
a questionnaire that was followed by a home visit, during which additional
ples that were collected by using a DNA self-collection kit. Zygosity was
determined primarily by genotyping. There were 238 monozygotic (MZ) pairs
Table 3. Effect of 0, 1 or 2 334 alleles on male reports on the Partner Bonding Scale, marital crisis,
and marital status
Number of 334 alleles
Mean score for the Partner Bonding Scale in the three groups
Partner Bonding Scale48.0 (6.50)46.3 (6.16)45.5 (6.71)2, 1438.40 0.0004
Frequency and column-wise percentage of subjects reporting marital crisis/threat of divorce in the three groups
Have you experienced marital crisis or threat
of divorce during the last year?
2, 143 5.000.008
Frequency and column-wise percentage of subjects being married or cohabiting in the three groups
Values for the Partner Bonding Scale are means with standard deviation in brackets.
Table 4. Association between 334 alleles in men and their wives’ reports of marital qualities
One or two 334
Dyadic satisfactionUnadjusted 43.3 (3.14)43.2 (2.92)
?0.12 1, 1110.49 0.49
Mean, Mean value on the outcome for the different DAS Scales for wives with standard deviation within
brackets. Adjusted, Analysis with the Partner Bonding Scale included as a covariate. The category of subjects not
carrying any 334 allele was used as reference group when constructing the regression estimates (? ). Analyses of
adjusted values were only performed for the scales that were significantly associated with the 334 allele in the
Walum et al.
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and 314 dizygotic (DZ) pairs. In total, 2,186 adult individuals were included in Download full-text
the study, of which 1,899 provided usable DNA samples.
Partner Bonding Scale. The pair bond is a critical element in the study of the
evolution of primate social organization (21). Pair bonds among nonhuman
primates are generally assessed by measures of partner specific affiliative
interaction, proximity, and reciprocity between two individuals (22–24). Fur-
thermore, the strength and stability of the bond is related to its persistence
the DAS (19), a frequently used assessment of the quality of marital relation-
ships and similar dyads, the Support Seeking and Giving (SSG) (26) assessment
measuring subjects’ engagement with other people, and the Marital Instabil-
occurrence of partner exclusive actions (for example, ‘‘How often do you kiss
your mate?’’). Proximity measures, which in nonhuman primates are mea-
sured as the amount of spatial closeness between two individuals, were
assessed by two types of items: The proband’s experiences of closeness to
other people (for example, ‘‘I don’t like when other people come too close to
me’’) and items concerning the proband’s motivation to spend time together
in common interests outside the family?’’). Because one requirement for
inclusion in the TOSS dataset was that the adult individuals were part of a
dyadic relationship that had persisted for at least five years, no information
‘‘Have you discussed a divorce or separation with a close friend?’’) were used
as individual indicators of future persistence of the relationship. No relevant
measures of reciprocity could be found in the TOSS dataset. Thus, of a total of
49 items, 18 questions (7 DAS, 10 SSG, and 1 MIS) were considered relevant
with loadings ?0.4 on the first principal component were excluded [see
supporting information (SI) Table S1] resulting in the final PBS, which were
created as the sum of 13 items (7 DAS, 5 SSG, and 1 MIS), with scores ranging
from 5 to 66. The reliability, as measured with Cronbach’s alpha, was 0.79.
Validity estimates of the PBS and the original subscales of the validated
questionnaires showed plausible patterns of moderate to high correlation
coefficients (r ? .40–.75). These results were confirmed by our findings on
known-groups validity, which showed significant differences between mar-
ried and nonmarried subjects (F1,105? 28.28, P ? 0.0001), with nonmarried
subjects scoring lower on the PBS. We also observed that subjects that had
experienced during the last year marital crisis/threat of divorce scored signif-
icantly lower on the PBS than those who had not (F1,162? 186.22, P ? 0.0001).
By using the fact that the studied population comprised twin pairs, we finally
for dizygotic (DZ) males. The corresponding figures were 0.47 and 0.33 for
females. Heritability according to Falconer’s formula (h2? 2(rMZ? rDZ)) (28)
was 0.27 for men and 0.28 for women, similar to what has been observed for
marital satisfaction (29) and divorce (30).
Microsatellite Genotyping. The GT25repeat polymorphism was amplified with
primers 5?-TGTCAGACAAAACGCTGTTC-3? (forward) and 5?-TGTGGCTTTA-
AAAGTTATCCAG-3? (reverse), the RS3 repeat polymorphism was amplified
with primers 5?-TCCTGTAGAGATGTAAGTGC-3? (forward) and 5?-gtttcttTCT-
GGAAGAGACTTAGATGG-3? (reverse) (11, 12, 17), and the RS1 repeat poly-
morphism was amplified with primers 5?-AGGGACTGGTTCTACAATCTGC-3?
rescently labeled DNA fragments were analyzed by size with automated
capillary electrophoresis by using an ABI PRISM 3730 Genetic Analyzer (Ap-
Statistical Analysis. Statistical associations between the continuous and cate-
gorical predictors on the one hand and continuous and binary criteria on the
other were estimated by using Generalized Linear Mixed Effects Models
(GLMM). As earlier studies have shown that the effects of vasopressin on
for men and women separately.
To take the correlated data structure into account and to avoid estimation
problems, different variance-covariance matrices were modeled for monozy-
gotic twins, spouses to monozygotic twins, dizygotic twins, and spouses to
dizygotic twins. Each of these four groups had a cluster size of n ? 2. The
correlations between individuals in these groups were calculated by using
R-side random effects with an unstructured variance-covariance matrix. The
an identity link function between the predictor term and the criterion. Di-
chotomous outcomes were assumed to be binary distributed with a logit link
function. The parameters were estimated based on the residual log pseudo-
likelihood (RSPL), which is equivalent to restricted maximum likelihood (31).
All statistical analysis was performed by using the Statistical Analysis System
(SAS), Version 9.1.3 (32), and generalized linear mixed effects models were
implemented by using the PROC GLIMMIX procedure.
ACKNOWLEDGMENTS. This project was supported by National Institute of
Grant J2004–0036:1, and a postdoctoral fellowship sponsored by the Brain
Foundation, Sweden (to L.W.).
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