Chronic and acute stress, gender, and serotonin transporter gene-environment interactions predicting depression symptoms in youth

Serotonin transporter gene as a predictor of stress generation in depression

Research suggests that a polymorphism in the promoter region of the serotonin transporter promoter (5-HTTLPR) interacts with stressful life events to predict depressive onset, with short (s) allele presence associated with greater susceptibility to stressors. However, this research has not considered that depressed individuals often actively generate stressful contexts. Furthermore, little is known about the genetic basis of stress generation. The current study explored the role of 5-HTTLPR genotype in stress generation in a longitudinal sample of 381 adolescents, oversampled for maternal depression, assessed at ages 15 and 20. Genotype did not correlate directly with number or ratings of stressful life events. However, 5-HTTLPR genotype interacted with depression at age 15 to predict dependent stressful events at age 20. Specifically, participants with one or more s alleles showed a stronger association between age 15 depression and age 20 dependent and interpersonal events than long allele homozygotes. Results imply that the 5-HTTLPR genotype predicts reciprocal associations between stress and depression, indicating a more complex relationship between stress, depression, and their genetic underpinnings than previously suggested.

Contemporary Genetics for Gender Researchers

Over the past century, much of genetics was deterministic, and feminist researchers framed justified criticisms of genetics research. However, over the past two decades, genetics research has evolved remarkably and has moved far from earlier deterministic approaches. Our article provides a brief primer on modern genetics, emphasizing contemporary evidence for the complex interplay between genes and environment. We focus particularly on the role of gene–environment interactions for gender-imbalanced disorders such as depression. We review research on epigenetics, which is one mechanism by which environment influences gene expression. Modern genetics is not based on a model of genetic determinism; instead, it recognizes the complexity of genetic influences and the nuanced interplay between genes and environment across life span development. Even with the modern genetics approaches, of course, there is still room for criticism and input from gender researchers. We outline methodological and conceptual issues more generally and from a gender researcher’s perspective. We argue that, with interdisciplinary collaborations, modern genetics can be integrated into gender research and vice versa in ways that will create progress in both fields.

Future directions in vulnerability to depression among youth: integrating risk factors and processes across multiple levels of analysis

Depression is a developmental phenomenon. Considerable progress has been made in describing the syndrome, establishing its prevalence and features, providing clues as to its etiology, and developing evidence-based treatment and prevention options. Despite considerable headway in distinct lines of vulnerability research, there is an explanatory gap in the field's ability to more comprehensively explain and predict who is likely to become depressed, when, and why. Still, despite clear success in predicting moderate variance for future depression, especially with empirically rigorous methods and designs, the heterogeneous and multi-determined nature of depression suggests that additional etiologies need to be included to advance knowledge on developmental pathways to depression. This paper advocates for a multiple levels of analysis approach to investigating vulnerability to depression across the lifespan and providing a more comprehensive understanding of its etiology. One example of a multiple levels of analysis model of vulnerabilities to depression is provided that integrates the most accessible, observable factors (e.g., cognitive and temperament risks), intermediate processes and endophenotypes (e.g., information-processing biases, biological stress physiology, and neural activation and connectivity), and genetic influences (e.g., candidate genes and epigenetics). Evidence for each of these factors as well as their cross-level integration is provided. Methodological and conceptual considerations important for conducting integrative, multiple levels of depression vulnerability research are discussed. Finally, translational implications for how a multiple levels of analysis perspective may confer additional leverage to reduce the global burden of depression and improve care are considered.

The 5-HTTLPR polymorphism moderates the effect of stressful life events on drinking behavior in college students of African descent

Covault et al. [Covault et al. (2007); Biol Psychiatry 61(5): 609-616] reported that the common functional polymorphism, 5-HTTLPR, in the serotonin transporter gene moderated the association between past-year stressful events and daily reports of drinking in a sample of European-American (EA) college students. We examined this effect in college students of African descent. Students recruited at a Historically Black University (n = 564) completed web-based measures of past-year stressful life experiences and daily reports of drinking and heavy drinking over a 30-day period. Participants were genotyped for the tri-allelic 5-HTTLPR polymorphism and dichotomized as low-activity S' allele carriers or high-activity L' homozygotes. Generalized linear models were used to examine the effects of life stress, genotype, and their interaction on the two drinking measures. In students who completed 15 or more daily surveys (n = 393), there was a significant interaction of past-year stressful events, 5-HTTLPR genotype, and gender on the number of drinking days (P = 0.002). Similar findings were obtained in relation to heavy drinking days (P = 0.007). Men showed a main effect of past-year stressful events on both drinking outcomes (P's < 0.001), but no main or moderator effects of genotype. In women, the S' allele moderated the impact of past-year life stressors on the frequency of drinking and heavy drinking days (P's < 0.001). In college students of African descent, past-year stressful events were associated with more frequent drinking and heavy drinking, an effect that was moderated by the 5-HTTLPR polymorphism. However, in contrast to the findings in EA students, in the current sample, 5-HTTLPR moderated the association only among women.

Coaction of stress and serotonin transporter genotype in predicting aggression at the transition to adulthood

Despite consistent evidence that serotonin functioning affects stress reactivity and vulnerability to aggression, research on serotonin gene-stress interactions (G × E) in the development of aggression remains limited. The present study investigated variation in the promoter region of the serotonin transporter gene (5-HTTLPR) as a moderator of the stress-aggression association at the transition to adulthood. Multiple informants and multiple measures were used to assess aggression in a cohort of 381 Australian youth (61% female, 93% Caucasian) interviewed at ages 15 and 20. At age 20, semistructured interviews assessed acute and chronic stressors occurring in the past 12 months. Structural equation modeling analyses revealed a significant main effect of chronic stress, but not 5-HTTLPR or acute stress, on increases in aggression at age 20. Consistent with G × E hypotheses, 5-HTTLPR short allele carriers demonstrated greater increments in aggression following chronic stress relative to long allele homozygotes. The strength of chronic stress G × E did not vary according to sex. Variation at 5-HTTLPR appears to contribute to individual differences in aggressive reactions to chronic stress at the transition to adulthood.

Developmental risk of depression: experience matters

This article focuses on discussing risks for depression onset and the role of environmental factors in promoting resilience in children and adolescents. The authors review the current literature on specific (eg, family history of depression) and nonspecific (eg, poverty, stressful life events) risk factors for youth depression to underscore the need for prevention efforts promoting resiliency in this population.

Response time variability and response inhibition predict affective problems in adolescent girls, not in boys: the TRAILS study

The present study examines the relationship between neurocognitive functioning and affective problems through adolescence, in a cross-sectional and longitudinal perspective. Baseline response speed, response speed variability, response inhibition, attentional flexibility and working memory were assessed in a cohort of 2,179 adolescents (age 10-12 years) from the TRacking Adolescents' Individual Lives Survey (TRAILS). Affective problems were measured with the DSM-oriented Affective Problems scale of the Youth Self Report at wave 1 (baseline assessment), wave 2 (after 2.5 years) and wave 3 (after 5 years). Cross-sectionally, baseline response speed, response time variability, response inhibition and working memory were associated with baseline affective problems in girls, but not in boys. Longitudinally, enhanced response time variability predicted affective problems after 2.5 and 5 years in girls, but not in boys. Decreased response inhibition predicted affective problems after 5 years follow-up in girls, and again not in boys. The results are discussed in light of recent insights in gender differences in adolescence and state-trait issues in depression.

Stressful life events and the serotonin transporter gene (5-HTT) in recurrent clinical depression

BACKGROUND

An interaction between recent stressful life events (SLEs) and a serotonin transporter promoter polymorphism (5-HTTLPR) in depression has been inconsistently reported. Some of this variability may be due to a previous focus on sub-clinical depression, inclusion of individuals at the lower or upper ends of the age-span, or assumptions concerning the degree of dominance of the low expressing allele. Therefore, a large sample of patients with recurrent clinically diagnosed depression and controls screened for absence of depression was utilised to examine the moderating effect of each 5-HTTLPR genetic model on the association between SLEs and severe depressive episodes.

METHOD

A sample of 1236 recurrent unipolar depression cases and 598 age-matched, never psychiatrically ill controls completed the List of Threatening Experiences Questionnaire to assess the number of SLEs experienced in the 6 months prior to the most severe depressive episode (cases) or interview (controls). DNA extracted from blood or cheek swabs was genotyped for the short (s) and long (l) alleles of 5-HTTLPR.

RESULTS

A greater number of SLEs were reported by cases than controls and this held across all genotypic groups. There was no main effect of 5-HTTLPR on depression and no evidence of interaction between total SLEs and any of the 5-HTTLPR genetic models. The results were the same for men and women.

LIMITATIONS

Utilisation of retrospective self-reported SLEs may have reduced the accuracy of the findings and the cross-sectional design prevents causal inference.

CONCLUSIONS

This study failed to find evidence of gene-environment interplay in recurrent clinical depression.

Chronic family stress interacts with 5-HTTLPR to predict prospective depressive symptoms among youth

BACKGROUND

Previous research, predominantly with adults, has shown that the serotonin transporter gene (5-HTTLPR) interacts with stress (G × E) to predict depressive symptoms; however, few G × E studies have been conducted with youth using rigorous methods, particularly a prospective design and contextual interview to assess stress. This study examined the interaction between 5-HTTLPR and stress, both chronic and episodic, to predict longitudinal change in depressive symptoms among children and adolescents.

METHODS

A general community sample of youth (N = 200; 57% girls; mean age: 12.09 years old) was genotyped for 5-HTTLPR (rs 25531) at baseline. They were interviewed via contextual stress procedures to ascertain chronic family stress and episodic stressors and completed depressive symptoms questionnaires at baseline and 6 months later.

RESULTS

A significant G × E showed that chronic family stress predicted prospective increases in depressive symptoms over 6 months among youth possessing the high-risk S allele. This G × E was not found for episodic stressors occurring in the last 6 months. There was no moderation by sex or pubertal status.

CONCLUSIONS

These findings advance knowledge on G × E effects in depression among youth. This is the first study to show that chronic family stress, but not episodic stressors, when ascertained by rigorous stress interview, interacts with 5-HTTLPR to prospectively predict depressive symptoms among children and adolescents.

Research review: gene-environment interaction research in youth depression - a systematic review with recommendations for future research

BACKGROUND

Depression is a major public health problem among youth, currently estimated to affect as many as 9% of US children and adolescents. The recognition that both genes (nature) and environments (nurture) are important for understanding the etiology of depression has led to a rapid growth in research exploring gene-environment interactions (GxE). However, there has been no systematic review of GxE in youth depression to date.

METHODS

The goal of this article was to systematically review evidence on the contribution of GxE to the risk of child and adolescent depression. Through a search of PubMed and PsycINFO databases to 1 April 2010, we identified 20 candidate gene-environment interaction studies focused on depression in youth (up to age 26) and compared each study in terms of the following characteristics: research design and sample studied; measure of depression and environment used; genes explored; and GxE findings in relation to these factors.

RESULTS

In total, 80% of studies (n = 16) found at least one significant GxE association. However, there was wide variation in methods and analyses adopted across studies, especially with respect to environmental measures used and tests conducted to estimate GxE. This heterogeneity made it difficult to compare findings and evaluate the strength of the evidence for GxE.

CONCLUSIONS

The existing body of GxE research on depression in youth contains studies that are conceptually and methodologically quite different, which contributes to mixed findings and makes it difficult to assess the current state of the evidence. To decrease this heterogeneity, we offer 20 recommendations that are focused on: (a) reporting GxE research; (b) testing and reporting GxE effects; (c) conceptualizing, measuring and analyzing depression; (d) conceptualizing, measuring and analyzing environment; (e) increasing power to test for GxE; and (f) improving the quality of genetic data used. Although targeted to GxE research on depression, these recommendations can be adopted by GxE researchers focusing on other mental health outcomes.

Transmission and prevention of mood disorders among children of affectively ill parents: a review

OBJECTIVE

To provide a conceptual review of the literature on children of depressed parents over the past 12 years.

METHOD

This selective review focused on published studies that delineate the diagnosis of depression in parents, have large samples, describe children 6 to 17 years old, and are methodologically rigorous. The review emphasized conceptual advances and major progress since 1998. Recent efforts in prevention research were discussed, gaps in the existing literature were noted, and directions for targeted research on children of depressed parents were highlighted.

RESULTS

Over the past 12 years there has been considerable progress in delineating the gene-by-environment interplay in determining the range of outcomes in children. In addition, progress has been made in identifying risk mechanisms and moderators that underlie the transmission of disorder and in developing effective prevention programs.

CONCLUSIONS

This review highlights directions for further research, including different areas affected by parental depression in parents and children, and in understanding the underlying mechanisms involved in the intergenerational transmission of depression, so that preventive and treatment efforts can be tailored effectively.

Droplets of black bile? Development of vulnerability and resilience to depression in young age

Major depressive disorder is predicted by enduring anxiety-related personality traits, in particular by neuroticism, which have genetic foundations. Neuroticism in turn is strongly related with the genetic risk for depression. Search for gene variants associated with neuroticism and depression has led to some good candidates, but the consistency of findings is very far from ideal. Adverse life events are causal to development of mood disorders, and often the vulnerability genes can be detected only when environmental impact has been objectively assessed. Yet the continuity of depression diagnosis from early childhood to adulthood is limited, while childhood depression increases odds of other affect-related disorders such as substance abuse and personality disorders. Whether specific genes have an impact seems to depend on the period of life both because of biological maturation and differences in major environmental factors, but also active engagement--or the failure to do so--of the vulnerable subjects with their environment. It is proposed that subjects with genetically determined neurotic tendencies are likely to attempt to select coping strategies that reduce events perceived as harmful and can by this means develop resilience towards affective disorders.

Gene-environment interactions: early life stress and risk for depressive and anxiety disorders

RATIONALE

Prior reviews have examined how stress, broadly defined, interacts with genetic diathesis in the pathogenesis of internalizing (i.e., depressive and anxiety) disorders. Recent findings have suggested a unique role for early life stress (ELS) in the development of internalizing disorders, contributing to the rapid proliferation of research in this area.

OBJECTIVE

This paper critically reviews studies in humans examining gene-environment interaction (GxE) effects of ELS on the risk for depression and anxiety, primarily from a candidate gene perspective. Major methodological challenges that are unique to such studies are considered.

RESULTS

The majority of published studies have focused on candidates that regulate the serotonin system, especially the serotonin transporter. More recent work has addressed interactions of ELS with candidates from the hypothalamic-pituitary-adrenal axis and neurotrophin system. Available studies vary greatly with respect to definitions of ELS, examination of gene-gene interactions, consideration of gender effects, and attention to analytic limitations.

CONCLUSIONS

Overall, there is support for GxE effects of ELS on the risk for depressive and anxiety outcomes. Future studies of ELS in this context will require careful attention to methodologic considerations. Such studies would benefit from more systematic assessment of positive environmental factors (e.g., social support) and greater utilization of developmentally sensitive paradigms.

The serotonin transporter promoter variant (5-HTTLPR), stress, and depression meta-analysis revisited: evidence of genetic moderation

CONTEXT

Two recent meta-analyses assessed the set of studies exploring the interaction between a serotonin transporter promoter polymorphism (5-HTTLPR) and stress in the development of depression and concluded that the evidence did not support the presence of the interaction. However, even the larger of the meta-analyses included only 14 of the 56 studies that have assessed the relationship between 5-HTTLPR, stress, and depression.

OBJECTIVE

To perform a meta-analysis including all relevant studies exploring the interaction.

DATA SOURCES

We identified studies published through November 2009 in PubMed.

STUDY SELECTION

We excluded 2 studies presenting data that were included in other larger studies.

DATA EXTRACTION

To perform a more inclusive meta-analysis, we used the Liptak-Stouffer z score method to combine findings of primary studies at the level of significance tests rather than the level of raw data.

DATA SYNTHESIS

We included 54 studies and found strong evidence that 5-HTTLPR moderates the relationship between stress and depression, with the 5-HTTLPR s allele associated with an increased risk of developing depression under stress (P = .00002). When stratifying our analysis by the type of stressor studied, we found strong evidence for an association between the s allele and increased stress sensitivity in the childhood maltreatment (P = .00007) and the specific medical condition (P = .0004) groups of studies but only marginal evidence for an association in the stressful life events group (P = .03). When restricting our analysis to the studies included in the previous meta-analyses, we found no evidence of association (Munafò et al studies, P = .16; Risch et al studies, P = .11). This suggests that the difference in results between meta-analyses was due to the different set of included studies rather than the meta-analytic technique.

CONCLUSION

Contrary to the results of the smaller earlier meta-analyses, we find strong evidence that the studies published to date support the hypothesis that 5-HTTLPR moderates the relationship between stress and depression.

Interaction of 5-HTTLPR and idiographic stressors predicts prospective depressive symptoms specifically among youth in a multiwave design

5-HTTLPR, episodic stressors, depressive and anxious symptoms were assessed prospectively (child and parent report) every 3 months over 1 year (5 waves of data) among community youth ages 9 to 15 (n = 220). Lagged hierarchical linear modeling analyses showed 5-HTTLPR interacted with idiographic stressors (increases relative to the child's own average level over time), but not nomothetic stressors (higher stress exposure relative to the sample), to predict prospective elevations in depressive, but not anxious, symptoms. Youth with copies of the S or L(G) alleles of 5-HTTLPR, who experienced more stressors relative to their typical level, exhibited prospective increases in depressive symptoms over time. These findings suggest that 5-HTTLPR confers susceptibility to depression via stress reactivity.

Genetics of childhood and adolescent depression: insights into etiological heterogeneity and challenges for future genomic research

There is heterogeneity between depression in childhood, adolescence and adulthood in terms of the gender composition of affected cases, prevalence, rates of recurrence and risk factors. This raises complex questions for refining the phenotype for molecular genetic studies of depression and the selection of appropriate proband groups. This article aims to provide a review of issues arising from family, twin and adoption studies of relevance to molecular genetic studies, and to summarize molecular genetic findings on childhood/adolescent depression. While retrospective studies of adults suggest greater familial aggregation among those with an earlier age of onset, prospective studies do not confirm this association. In fact, taken together, evidence from family and twin studies suggests that prepubertal depression is more strongly associated with psychosocial adversity, is less heritable and shows lower levels of continuity with adult depression than either adolescent or adult depression. Adolescent depressive symptoms and disorder show similar levels of heritability to depression in adult life, although there is only one twin study of adolescent depressive disorder, and heritability estimates of depressive symptoms vary widely between studies. This variability in heritability estimates is partly attributable to age and informant effects. Adoption studies and other intergenerational transmission designs show that the transmission of depression between parents and children involves genetic and environmental processes, with converging evidence that environmental processes are most important. Molecular genetic studies of childhood/adolescent depression have to date used a candidate gene approach and focused on genes already examined in adult studies. Prospective longitudinal studies of community and high-risk samples are needed to clarify issues of etiological heterogeneity in depression, and these should in turn inform the planning of molecular genetic studies.