Research paperA genetically informative analysis of the association between dyadic adjustment, depressive symptoms, and anxiety symptoms
Introduction
Poor marital adjustment is associated with mood, anxiety, and substance use disorders in population samples (McShall and Johnson, 2015, Whisman, 1999, Whisman, 2007). Many of these studies have examined how marital adjustment contributes to subsequent psychopathology, while acknowledging that psychopathology may also impact relationship adjustment (Whisman and Uebelacker, 2009). This study was conducted to examine genetic and environmental influences on the covariation between marital adjustment and symptoms of depression and anxiety in a sample of male and female twins and their spouse or long-term partner.
Much of the research on intimate relationships and psychopathology has focused on depression (Beach and Whisman, 2012, Whisman and Baucom, 2012). Cross-sectional studies suggest that poor marital adjustment is associated with higher levels of depressive symptoms (Proulx et al., 2007, Whisman, 2001) and prevalence of major depression (McShall and Johnson, 2015, Whisman, 1999, Whisman, 2007). Longitudinal studies suggest poor marital adjustment is associated with increases in depressive symptoms (Beach et al., 2003, Whisman and Uebelacker, 2009) and incidence of depressive disorders (Overbeek et al., 2006, Whisman and Bruce, 1999) in two-wave studies, and bidirectional associations between poor marital adjustment and depressive symptoms in multi-wave studies (Davila et al., 2003, Kouros et al., 2008, Whitton et al., 2008).
These results are consistent with the perspective that poor dyadic adjustment may be causally related to depression (Beach et al., 1990). However, stronger inferences regarding potential causal associations can be made if it is shown that these associations are not due to shared variance with other variables that could be causally associated both with poor dyadic adjustment and depression (McNamee, 2003). Studies have tried to rule out potential rival explanations by statistically adjusting for potential confounding variables, including personality traits (Cao et al., 2017, Vento and Cobb, 2011, Whisman et al., 2006), quality of participants’ relationships with their relatives and friends (Whisman et al., 2018, 2000), and self-esteem and stressful life events (Cao et al., 2017). Although these studies are important, they are typically limited because of measurement error in the assessment of confounding variables. Furthermore, as researchers must select which variables to control, and generally can only select a few variables, the assessment of confounding variables is not comprehensive (i.e., there are other unmeasured variables that could account for the association) (Irons et al., 2015).
One alternative to statistical control of potential confounds is to leverage genetically informative twin studies to account for unmeasured confounding variables and better understand potential causal associations between variables (Rutter, 2007). Because monozygotic (MZ) twins share 100% of their genes, whereas dizygotic (DZ) twins share only 50% of their segregating genes on average, and because twins reared together are raised in the same families at the same time, twin studies allow researchers to control for unmeasured genetic and shared environmental factors (i.e., environmental factors that lead siblings raised in the same family to be similar). If observed (i.e., phenotypic) associations between variables remain statistically significant after taking genetic and shared environmental confounds into account, then findings are consistent with a causal relationship; such phenotypic associations have been described as quasi-causal (Turkheimer and Harden, 2014). However, this approach cannot provide definitive evidence of a causal relationship, as the association may be explained by nonshared environmental influences, such as stressful life events, that lead to both poor marital adjustment and depression in one twin.
Research suggests there are genetic influences on dyadic adjustment (Spotts et al., 2004b, Spotts et al., 2006) and psychopathology (Burmeister et al., 2008), and researchers have begun to use genetically informative samples to account for genetic confounds that may explain the association between dyadic adjustment and psychopathology (for a review, see Whisman and South, 2017). In a study of female twins, there were shared genetic influences on the covariation between wives’ self-reported dyadic adjustment and depressive symptoms (Spotts et al., 2004a). Further evidence for shared genetic effects came from husband-reported dyadic adjustment, suggesting that a wife's genetically influenced characteristics may impact her own and her husband's dyadic adjustment. There was also evidence of non-shared environmental influences on the covariation between husbands’ report of dyadic adjustment and wives’ depressive symptoms, which may reflect the influence of partners’ characteristics (i.e., twins being married to different partners). Also, in a sample of male and female twins, the association between marital support and depressive symptoms was statistically significant after adjusting for genetic effects of marital support on depressive symptoms, suggesting that the association between marital support and depressive symptoms was not an artifact of selection (Beam et al., 2011).
Dyadic adjustment has also been found to covary with anxiety. For example, poor marital adjustment is associated with symptoms of anxiety (Leach et al., 2013) and anxiety disorders (McLeod, 1994, Pankiewicz et al., 2012, Whisman, 1999, Whisman, 2007). Furthermore, poor marital adjustment at baseline was associated with increased risk for incidence of the broad category of anxiety disorders (and the specific diagnosis of social phobia) two to three years later (Overbeek et al., 2006). However, we are not aware of any twin studies that have evaluated genetic and environmental influences on the covariation between dyadic adjustment and anxiety.
This study was conducted to examine the association between dyadic adjustment and symptoms of depression and anxiety in a sample of Swedish twins and their spouse or long-term partner.1 Both male and female twins and their partners were included, which allowed us to evaluate gender and respondent differences in genetic and environmental influences on the associations between variables. In addition, this is the first study known to us to examine genetic and environmental influences on the covariation between dyadic adjustment and anxiety symptoms. Consistent with the perspective that poor marital adjustment increases risk for psychopathology (Beach et al., 1990), we predicted that dyadic adjustment would be negatively associated with depressive and anxiety symptoms for both female and male twins, and that nonshared environmental influences would primarily account for these associations.
Section snippets
Participants
Participants were drawn from Cohort 2 of the Twin and Offspring Study in Sweden (TOSS; Neiderhiser and Lichtenstein, 2008), which consists of same-sex twin pairs born between 1944–1971, identified through The Swedish Twin Registry. To be eligible, each member of the twin pair (a) had to be involved in a long-term (i.e., ≥5-year) relationship with a partner residing in the same home; and (b) have an 11- to 22-year-old adolescent child who was the same sex as the co-twin's child with no more than
Results
Twin- and partner-reported dyadic adjustment were highly correlated (r = 0.58, p < .001), suggesting that twins and partners were consistent in their assessment and reporting of the level of adjustment in their relationships. There was also evidence of similarity between partners in depression and anxiety; depressive symptoms of twins and their partners were positively correlated (r = 0.20, p < .001), as were anxiety symptoms of twins and partners (r = 0.07, p = .03).
Discussion
This study examined genetic and environmental influences on the covariation between dyadic adjustment and symptoms of depression and anxiety in a sample of Swedish male and female twins and their spouse or long-term partner. The use of a genetically informative sample allowed us to conduct several analyses to test causal inferences between dyadic adjustment and psychopathology in relationship partners (Rutter, 2007). First, consistent with a potential causal hypothesis (De Moor et al., 2008),
Declarations of interest
None.
Conflict of interest
All authors declare that they have no conflicts of interest.
Contributors
Mark Whisman developed the study concept and assisted in writing the manuscript; Alta du Pont and Soo Rhee conducted the data analyses and assisted in writing the manuscript; Erica Spotts, Paul Lichtenstein, Jody Ganiban, David Reiss, and Jenae Neiderhiser provided critical and meaningful feedback for revision of the manuscript. All authors contributed to and have approved the final manuscript.
Funding
This work was supported by the National Institutes of Health [grant number MH054610]. The funding source had no role in the study design; in the collection, analysis and interpretation of the data; or in the decision to submit the article for publication.
Acknowledgment
None.
Limitations
Longitudinal research in genetically informative samples would provide a stronger test of the causal association between dyadic adjustment and psychopathology.
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