Stressful life events and depression among adolescent twin pairs

Genetic influences on depression and selection into adverse life experiences

Genome-wide association studies find that a large number of genetic variants jointly influence the risk of depression, which is summarized by polygenic indices (PGIs) of depressive symptoms and major depression. But PGIs by design remain agnostic about the causal mechanisms linking genes to depression. Meanwhile, the role of adverse life experiences in shaping depression risk is well-documented, including via gene-environment correlation. Building on theoretical work on dynamic and contingent genetic selection, we suggest that genetic influences may lead to differential selection into negative life experiences, forging gene-environment correlations that manifest in various permutations of depressive behaviors and environmental adversities. We also examine the extent to which apparent genetic influences may reflect spurious associations due to factors such as indirect genetic effects. Using data from two large surveys of middle-aged and older US adults, we investigate to what extent a PGI of depression predicts the risk of 27 different adversities. Further, to glean insights about the kinds of processes that might lead to gene-environment correlation, we augment these analyses with data from an original preregistered survey to measure cultural understandings of the behavioral dependence of various adversities. We find that the PGI predicts the risk of majority of adversities, net of class background and prior depression, and that the selection risk is greater for adversities typically perceived as being dependent on peoples' own behaviors. Taken together, our findings suggest that the PGI of depression largely picks up the risk of behaviorally-influenced adversities, but to a lesser degree also captures other environmental influences. The results invite further exploration into the behavioral and interactional processes that lie along the pathways intervening between genetic differences and wellbeing.

Examining the relationship between genetic risk for depression and youth episodic stress exposure

BACKGROUND

Offspring of depressed mothers have elevated risk of developing depression because they are exposed to greater stress. While generally assumed that youth's increased exposure to stress is due to the environmental effects of living with a depressed parent, youth's genes may influence stress exposure through gene-environment correlations (rGEs). To understand the relationship between risk for depression and stress, we examined the effects of polygenic risk for depression on youth stress exposure.

METHODS

We examined the relations of a polygenic risk score (PRS) for depression (DEP-PRS), as well as PRSs for 5 other disorders, with youth stress exposure. Data were from a longitudinal study of a community sample of youth and their parents (n = 377) focusing on data collected at youth's aged 12 and 15 assessments.

RESULTS

Elevated youth DEP-PRS was robustly associated with increased dependent stress, particularly interpersonal events. Exploratory analyses indicated that findings were driven by major stress and were not moderated by maternal nor paternal history of depression, and of the 5 additional PRSs tested, only elevated genetic liability for bipolar I was associated with increased dependent stress-particularly non-interpersonal events.

LIMITATIONS

Like other PRS studies, we focused on those of European ancestry thus, generalizability of findings is limited.

CONCLUSION

Polygenic risk contributes to youth experiencing stressful life events which are dependent on their behavior. This rGE appears to be specific to genetic risk for mood disorders.

Parent and Child Predictors of Internalizing and Externalizing Symptomatology during COVID-19

The COVID-19 emergency has fostered an increasing risk of experiencing distress and negative emotions in parents that turned into heightened stress for children. In this study, we aim to evaluate the effects of parental stress, children's resilience, and previous adversities on the development of internalizing and externalizing symptoms in children. A series of questionnaires were completed by 158 Italian parents (148 mothers, 10 fathers, mean age = 41 years) concerning them and their school-aged children (N = 158, 76 boys, mean age = 7.4 years) at two critical time points (June 2020 and December 2020). Regression analyses showed that internalizing problems were predicted only by concurrent children's resilience, whereas externalizing problems were predicted by concurrent parental flooding, children's resilience, and early parental satisfaction. Therefore, internalizing and externalizing symptoms trajectories follow different routes and are predicted by both common and distinct factors. Supporting positive parenting attitudes and behavior should be recommended to prevent the worsening of children's externalizing behaviors. At the same time, nurturing resilience in pediatric systems might be useful in preventing or reducing children's internalizing symptoms.

Family-based care buffers the stress sensitizing effect of early deprivation on executive functioning difficulties in adolescence

We examined whether family care following early-life deprivation buffered the association between stressful life events (SLEs) and executive functioning (EF) in adolescence. In early childhood, 136 institutionally reared children were randomly assigned to foster care or care-as-usual; 72 never-institutionalized children served as a comparison group. At age 16 years, adolescents (n = 143; 54% female; 67.1% Romanian) self-reported recent SLEs, completed a battery of memory and EF tasks, and completed a go/nogo task in which mediofrontal theta power (MFTP) was measured using electroencephalogram. More independent SLEs predicted lower EF and more dependent SLEs predicted lower MFTP, but only among adolescents with prolonged early deprivation. Findings provide preliminary evidence that family care following early deprivation may facilitate resilience against stress during adolescence on EF.

Associations between depression-relevant genetic risk and youth stress exposure: Evidence of gene-environment correlations

Familial risk for depression is associated with youth exposure to self-generated dependent stressful life events and independent events that are out of youth's control. Familial risk includes both genetic and environmental influences, raising the question of whether genetic influences, specifically, are associated with youth exposure to both dependent and independent stressful life events. To address this question, this study examined the relation between a genome-wide association study (GWAS)-derived depression-based polygenic risk score (DEP-PRS) and youth experiences of dependent and independent stress. Participants were 180 youth (ages 8 to 14, 52.2% female) of European ancestry and their biological mothers recruited based on the presence versus absence of a history of major depressive disorder (MDD) in the mothers. Youth and mothers were interviewed every 6 months for 2 years regarding the occurrence of stressful life events, which were coded as independent or dependent (self-generated). Results indicated that youth's DEP-PRS and maternal history of MDD were uniquely associated with increased exposure to both dependent and independent events. Similar results were observed when examining major versus minor events separately, with the additional finding of a DEP-PRS × mother MDD interaction for major dependent events such that levels of moderate to severe dependent life stressors were highest among youth with high DEP-PRSs who also had mothers with MDD. These results not only support the presence of depression-relevant gene-environment correlations (rGEs), but also highlight the possibility that rather than only capturing depression-specific genetic liability, GWAS-derived polygenic risk scores may also capture genetic variance contributing to stress exposure. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Negative life events and stress sensitivity in youth's daily life: an ecological momentary assessment study

PURPOSE

Negative life events (LEs) are associated with mental health problems in youth. However, little is known about underlying mechanisms. The aim of the study was to investigate whether exposure to LEs modifies stress sensitivity in youth's daily life.

METHODS

Ecological Momentary Assessment (EMA) was used to assess stress sensitivity (i.e., association of momentary stress with (i) negative affect and (ii) psychotic experiences) in 99 adolescents and young adults (42 service users, 17 siblings, and 40 controls; M_age 15 years). Before EMA, exposure to LEs (e.g., intrusive threats, experience of loss, serious illness) was assessed.

RESULTS

Lifetime as well as previous-year exposure to LEs modified stress sensitivity in service users: they experienced more intense negative affect and psychotic experiences in response to stress when high vs. low exposure levels were compared. In contrast, controls showed no differences in stress sensitivity by exposure levels. Looking at specific types of LEs, controls showed less intense negative affect in response to stress when high vs. low exposure levels to threatening events during the last year, but not lifetime exposure, were compared. In siblings, no evidence was found that LEs modified stress sensitivity.

CONCLUSION

Stress sensitivity may constitute a putative risk mechanism linking LEs and mental health in help-seeking youth, while unfavourable effects of LEs on stress sensitivity may attenuate over time or do not occur in controls and siblings. Targeting individuals' sensitivity to stress in daily life using novel digital interventions may be a promising approach towards improving youth mental health.

Predicting Alcohol Dependence Symptoms by Young Adulthood: A Co-Twin Comparisons Study

Co-twin comparisons address familial confounding by controlling for genetic and environmental influences that twin siblings share. We applied the co-twin comparison design to investigate associations of adolescent factors with alcohol dependence (AD) symptoms. Participants were 1286 individuals (581 complete twin pairs; 42% monozygotic; and 54% female) from the FinnTwin12 study. Predictors included adolescent academic achievement, substance use, externalizing problems, internalizing problems, executive functioning, peer environment, physical health, relationship with parents, alcohol expectancies, life events, and pubertal development. The outcome was lifetime AD clinical criterion count, as measured in young adulthood. We examined associations of each adolescent domain with AD symptoms in individual-level and co-twin comparison analyses. In individual-level analyses, adolescents with higher levels of substance use, teacher-reported externalizing problems at age 12, externalizing problems at age 14, self- and co-twin-reported internalizing problems, peer deviance, and perceived difficulty of life events reported more symptoms of AD in young adulthood (ps < .044). Conversely, individuals with higher academic achievement, social adjustment, self-rated health, and parent-child relationship quality met fewer AD clinical criteria (ps < .024). Associations between adolescent substance use, teacher-reported externalizing problems, co-twin-reported internalizing problems, peer deviance, self-rated health, and AD symptoms were of a similar magnitude in co-twin comparisons. We replicated many well-known adolescent correlates of later alcohol problems, including academic achievement, substance use, externalizing and internalizing problems, self-rated health, and features of the peer environment and parent-child relationship. Furthermore, we demonstrate the utility of co-twin comparisons for understanding pathways to AD. Effect sizes corresponding to the associations between adolescent substance use, teacher-reported externalizing problems, co-twin-reported internalizing problems, peer deviance, and self-rated health were not significantly attenuated (p value threshold = .05) after controlling for genetic and environmental influences that twin siblings share, highlighting these factors as candidates for further research.

Genetic and Environmental Influences on Stressful Life Events and their Associations with Executive Functions in Young Adulthood: A Longitudinal Twin Analysis

Although stress is frequently considered an environmental factor, dependent stressful life events (SLEs)--stressors that result from one's actions or behaviors--may in fact be evoked by a genetic liability. It has been suggested that dependent SLEs may be partially caused by poor executive function (EFs), higher-level cognitive abilities that enable individuals to implement goal-directed behavior. We investigated the possibility of genetic and environmental overlap between SLEs and EFs in a longitudinal twin study. We found high genetic stability in the number of dependent SLEs from age 23 to age 29, suggesting that the number of dependent stressors show persistence across time due to their genetic etiology. In addition, there was a nominally significant negative genetic correlation between a Common EF latent factor and dependent SLEs at age 23. The genetic stability of dependent SLEs and association with Common EF provides insight into how some behaviors may lead to persistent stress.

Genome-wide gene-environment analyses of major depressive disorder and reported lifetime traumatic experiences in UK Biobank

Depression is more frequent among individuals exposed to traumatic events. Both trauma exposure and depression are heritable. However, the relationship between these traits, including the role of genetic risk factors, is complex and poorly understood. When modelling trauma exposure as an environmental influence on depression, both gene-environment correlations and gene-environment interactions have been observed. The UK Biobank concurrently assessed Major Depressive Disorder (MDD) and self-reported lifetime exposure to traumatic events in 126,522 genotyped individuals of European ancestry. We contrasted genetic influences on MDD stratified by reported trauma exposure (final sample size range: 24,094-92,957). The SNP-based heritability of MDD with reported trauma exposure (24%) was greater than MDD without reported trauma exposure (12%). Simulations showed that this is not confounded by the strong, positive genetic correlation observed between MDD and reported trauma exposure. We also observed that the genetic correlation between MDD and waist circumference was only significant in individuals reporting trauma exposure (rg = 0.24, p = 1.8 × 10-7 versus rg = -0.05, p = 0.39 in individuals not reporting trauma exposure, difference p = 2.3 × 10-4). Our results suggest that the genetic contribution to MDD is greater when reported trauma is present, and that a complex relationship exists between reported trauma exposure, body composition, and MDD.

Association of Maternal Neurodevelopmental Risk Alleles With Early-Life Exposures

Importance

Early-life exposures, such as prenatal maternal lifestyle, illnesses, nutritional deficiencies, toxin levels, and adverse birth events, have long been considered potential risk factors for neurodevelopmental disorders in offspring. However, maternal genetic factors could be confounding the association between early-life exposures and neurodevelopmental outcomes in offspring, which makes inferring a causal relationship problematic.

Objective

To test whether maternal polygenic risk scores (PRSs) for neurodevelopmental disorders were associated with early-life exposures previously linked to the disorders.

Design, Setting, and Participants

In this UK population-based cohort study, 7921 mothers with genotype data from the Avon Longitudinal Study of Parents and Children (ALSPAC) underwent testing for association of maternal PRS for attention-deficit/hyperactivity disorder (ADHD PRS), autism spectrum disorder (ASD PRS), and schizophrenia (SCZ PRS) with 32 early-life exposures. ALSPAC data collection began September 6, 1990, and is ongoing. Data were analyzed for the current study from April 1 to September 1, 2018.

Exposures

Maternal ADHD PRS, ASD PRS, and SCZ PRS were calculated using discovery effect size estimates from the largest available genome-wide association study and a significance threshold of P < .05.

Main Outcomes and Measures

Outcomes measured included questionnaire data on maternal lifestyle and behavior (eg, smoking, alcohol consumption, body mass index, and maternal age), maternal use of nutritional supplements and medications in pregnancy (eg, acetaminophen, iron, zinc, folic acid, and vitamins), maternal illnesses (eg, diabetes, hypertension, rheumatism, psoriasis, and depression), and perinatal factors (eg, birth weight, preterm birth, and cesarean delivery).

Results

Maternal PRSs were available from 7921 mothers (mean [SD] age, 28.5 [4.8] years). The ADHD PRS was associated with multiple prenatal factors, including infections (odds ratio [OR], 1.11; 95% CI, 1.04-1.18), use of acetaminophen during late pregnancy (OR, 1.11; 95% CI, 1.04-1.18), lower blood levels of mercury (β coefficient, -0.06; 95% CI, -0.11 to -0.02), and higher blood levels of cadmium (β coefficient, 0.07; 95% CI, 0.05-0.09). Little evidence of associations between ASD PRS or SCZ PRS and prenatal factors or of association between any of the PRSs and adverse birth events was found. Sensitivity analyses revealed consistent results.

Conclusions and Relevance

These findings suggest that maternal risk alleles for neurodevelopmental disorders, primarily ADHD, are associated with some pregnancy-related exposures. These findings highlight the need to carefully account for potential genetic confounding and triangulate evidence from different approaches when assessing the effects of prenatal exposures on neurodevelopmental disorders in offspring.

Genome-wide by environment interaction studies of depressive symptoms and psychosocial stress in UK Biobank and Generation Scotland

Stress is associated with poorer physical and mental health. To improve our understanding of this link, we performed genome-wide association studies (GWAS) of depressive symptoms and genome-wide by environment interaction studies (GWEIS) of depressive symptoms and stressful life events (SLE) in two UK population-based cohorts (Generation Scotland and UK Biobank). No SNP was individually significant in either GWAS, but gene-based tests identified six genes associated with depressive symptoms in UK Biobank (DCC, ACSS3, DRD2, STAG1, FOXP2 and KYNU; p < 2.77 × 10-6). Two SNPs with genome-wide significant GxE effects were identified by GWEIS in Generation Scotland: rs12789145 (53-kb downstream PIWIL4; p = 4.95 × 10-9; total SLE) and rs17070072 (intronic to ZCCHC2; p = 1.46 × 10-8; dependent SLE). A third locus upstream CYLC2 (rs12000047 and rs12005200, p < 2.00 × 10-8; dependent SLE) when the joint effect of the SNP main and GxE effects was considered. GWEIS gene-based tests identified: MTNR1B with GxE effect with dependent SLE in Generation Scotland; and PHF2 with the joint effect in UK Biobank (p < 2.77 × 10-6). Polygenic risk scores (PRSs) analyses incorporating GxE effects improved the prediction of depressive symptom scores, when using weights derived from either the UK Biobank GWAS of depressive symptoms (p = 0.01) or the PGC GWAS of major depressive disorder (p = 5.91 × 10-3). Using an independent sample, PRS derived using GWEIS GxE effects provided evidence of shared aetiologies between depressive symptoms and schizotypal personality, heart disease and COPD. Further such studies are required and may result in improved treatments for depression and other stress-related conditions.

Genetic and environmental determinants of stressful life events and their overlap with depression and neuroticism

Background: Stressful life events (SLEs) and neuroticism are risk factors for major depressive disorder (MDD). However, SLEs and neuroticism are heritable and genetic risk for SLEs is associated with risk for MDD. We sought to investigate the genetic and environmental contributions to SLEs in a family-based sample, and quantify genetic overlap with MDD and neuroticism. Methods: A subset of Generation Scotland: the Scottish Family Health Study (GS), consisting of 9618 individuals with information on MDD, past 6 month SLEs, neuroticism and genome-wide genotype data was used in the present study. We estimated the heritability of SLEs using GCTA software. The environmental contribution to SLEs was assessed by modelling familial, couple and sibling components. Using polygenic risk scores (PRS) and LD score regression (LDSC) we analysed the genetic overlap between MDD, neuroticism and SLEs. Results: Past 6-month life events were positively associated with lifetime MDD status (β=0.21, r ²=1.1%, p=2.5 x 10 ^-25) and neuroticism (β =0.13, r ²=1.9%, p=1.04 x 10 ^-37) at the phenotypic level.  Common SNPs explained 8% of the phenotypic variance in personal life events (those directly affecting the individual) (S.E.=0.03, p= 9 x 10 ^-4). A significant effect of couple environment was detected accounting for 13% (S.E.=0.03, p=0.016) of the phenotypic variation in SLEs. PRS analyses found that reporting more SLEs was associated with a higher polygenic risk for MDD (β =0.05, r ²=0.3%, p=3 x 10 ^-5), but not a higher polygenic risk for neuroticism. LDSC showed a significant genetic correlation between SLEs and both MDD (r _G=0.33, S.E.=0.08 ) and neuroticism (r _G=0.15, S.E.=0.07). Conclusions: These findings suggest that SLEs should not be regarded solely as environmental risk factors for MDD as they are partially heritable and this heritability is shared with risk for MDD and neuroticism. Further work is needed to determine the causal direction and source of these associations.

Genetic and environmental determinants of stressful life events and their overlap with depression and neuroticism

Background: Stressful life events (SLEs) and neuroticism are risk factors for major depressive disorder (MDD). However, SLEs and neuroticism are heritable and genetic risk for SLEs is associated with risk for MDD. We sought to investigate the genetic and environmental contributions to SLEs in a family-based sample, and quantify genetic overlap with MDD and neuroticism.

Methods: A subset of Generation Scotland: the Scottish Family Health Study (GS), consisting of 9618 individuals with information on MDD, past 6 month SLEs, neuroticism and genome-wide genotype data was used in the present study. We estimated the heritability of SLEs using GCTA software. The environmental contribution to SLEs was assessed by modelling familial, couple and sibling components. Using polygenic risk scores (PRS) and LD score regression (LDSC) we analysed the genetic overlap between MDD, neuroticism and SLEs.

Results: Past 6-month life events were positively associated with lifetime MDD status (β=0.21, r ²=1.1%, p=2.5 x 10 ^-25) and neuroticism (β =0.13, r ²=1.9%, p=1.04 x 10 ^-37) at the phenotypic level.  Common SNPs explained 8% of the phenotypic variance in personal life events (those directly affecting the individual) (S.E.=0.03, p= 9 x 10 ^-4). A significant effect of couple environment was detected accounting for 13% (S.E.=0.03, p=0.016) of the phenotypic variation in SLEs. PRS analyses found that reporting more SLEs was associated with a higher polygenic risk for MDD (β =0.05, r ²=0.3%, p=3 x 10 ^-5), but not a higher polygenic risk for neuroticism. LDSC showed a significant genetic correlation between SLEs and both MDD (r _G=0.33, S.E.=0.08 ) and neuroticism (r _G=0.15, S.E.=0.07).

Conclusions: These findings suggest that SLEs should not be regarded solely as environmental risk factors for MDD as they are partially heritable and this heritability is shared with risk for MDD and neuroticism. Further work is needed to determine the causal direction and source of these associations.

A direct test of the diathesis-stress model for depression

The diathesis-stress theory for depression states that the effects of stress on the depression risk are dependent on the diathesis or vulnerability, implying multiplicative interactive effects on the liability scale. We used polygenic risk scores for major depressive disorder (MDD) calculated from the results of the most recent analysis from the Psychiatric Genomics Consortium as a direct measure of the vulnerability for depression in a sample of 5221 individuals from 3083 families. In the same we also had measures of stressful life events and social support and a depression symptom score, as well as DSM-IV MDD diagnoses for most individuals. In order to estimate the variance in depression explained by the genetic vulnerability, the stressors and their interactions, we fitted linear mixed models controlling for relatedness for the whole sample as well as stratified by sex. We show a significant interaction of the polygenic risk scores with personal life events (0.12% of variance explained, P-value=0.0076) contributing positively to the risk of depression. Additionally, our results suggest possible differences in the aetiology of depression between women and men. In conclusion, our findings point to an extra risk for individuals with combined vulnerability and high number of reported personal life events beyond what would be expected from the additive contributions of these factors to the liability for depression, supporting the multiplicative diathesis-stress model for this disease.

Lingual Gyrus Surface Area Is Associated with Anxiety-Depression Severity in Young Adults: A Genetic Clustering Approach

Here we aimed to identify cortical endophenotypes for anxiety-depression. Our data-driven approach used vertex-wise genetic correlations (estimated from a twin sample: 157 monozygotic and 194 dizygotic twin pairs) to parcellate cortical thickness (CT) and surface area (SA) into genetically homogeneous regions (Chen et al., 2013). In an overlapping twin and sibling sample (n = 834; aged 15–29, 66% female), in those with anxiety-depression Somatic and Psychological Health Report (SPHERE) scores (Hickie et al., 2001) above median, we found a reduction of SA in an occipito-temporal cluster, which comprised part of the right lingual, fusiform and parahippocampal gyrii. A similar reduction was observed in the Human Connectome Project (HCP) sample (n = 890, age 22–37, 56.5% female) in those with Adult Self Report (ASR) DSM-oriented scores (Achenbach et al., 2005) in the 25–95% quantiles. A post hoc vertex-wise analysis identified the right lingual and, to a lesser extent the fusiform gyrus. Overall, the surface reduction explained by the anxiety-depression scores was modest (r = −0.10, 3rd order spline, and r = −0.040, 1st order spline in the HCP). The discordant results in the top 5% of the anxiety-depression scores may be explained by differences in recruitment between the studies. However, we could not conclude whether this cortical region was an endophenotype for anxiety-depression as the genetic correlations did not reach significance, which we attribute to the modest effect size (post hoc statistical power <10%).

Genetic and environmental influences on last-year major depression in adulthood: a highly heritable stable liability but strong environmental effects on 1-year prevalence

BACKGROUND

This study seeks to clarify the contribution of temporally stable and occasion-specific genetic and environmental influences on risk for major depression (MD).

METHOD

Our sample was 2153 members of female-female twin pairs from the Virginia Twin Registry. We examined four personal interview waves conducted over an 8-year period with MD in the last year defined by DSM-IV criteria. We fitted a structural equation model to the data using classic Mx. The model included genetic and environmental risk factors for a latent, stable vulnerability to MD and for episodes in each of the four waves.

RESULTS

The best-fit model was simple and included genetic and unique environmental influences on the latent liability to MD and unique wave-specific environmental effects. The path from latent liability to MD in the last year was constant over time, moderate in magnitude (+0.65) and weaker than the impact of occasion-specific environmental effects (+0.76). Heritability of the latent stable liability to MD was much higher (78%) than that estimated for last-year MD (32%). Of the total unique environmental influences on MD, 13% reflected enduring consequences of earlier environmental insults, 17% diagnostic error and 70% wave-specific short-lived environmental stressors.

CONCLUSIONS

Both genetic influences on MD and MD heritability are stable over middle adulthood. However, the largest influence on last-year MD is short-lived environmental effects. As predicted by genetic theory, the heritability of MD is increased substantially by measurement at multiple time points largely through the reduction of the effects of measurement error and short-term environmental risk factors.

Environmental risks outweigh dopaminergic genetic risks for alcohol use and abuse from adolescence through early adulthood

BACKGROUND

Alcohol use is a primary public health concern, particularly among adolescents and young adults. Based on the rapidly growing field of gene-environment models, this study assessed the combined role of environmental and dopamine-related genetic correlates of early alcohol use and abuse.

METHODS

Multilevel growth models assessed trajectories of alcohol use and intoxication and ordered logistic regressions assessed alcohol use disorder among a sample of 12,437 youth from the nationally representative Add Health study who were followed from mid-adolescence through early adulthood.

RESULTS

Endogenous and exogenous stressful life events and social norms supportive of alcohol use from parents and peers were significant predictors of alcohol use, intoxication, and alcohol use disorder, with consistent patterns across males and females. In contrast, a dopamine-system genetic risk score (GRS) was not associated with alcohol use trajectories nor alcohol use disorder in early adulthood, although weak connections emerged between the GRS and growth trajectories of intoxication, indicating that higher GRS predicted more frequent episodes of intoxication during the transition to adulthood but not during adolescence or later 20s. No evidence of gene-environment interactions emerged.

CONCLUSIONS

Results extend a substantial body of prior research primarily assessing single genetic polymorphisms in the dopamine system, suggesting that dopaminergic GRSs may be associated with more problematic alcohol behaviors at some developmental periods, but further, that social norms and stressful life experiences are more consistent correlates of early and problematic alcohol use among youth. These environmental factors present potential targets for research manipulating contexts to identify causal pathways.

Genetic and Environmental Overlap Between Childhood Maltreatment and Adult Physical Health

Past research demonstrates a phenotypic relationship between childhood maltreatment and adult health problems. Explanations of this association usually point to either: (a) a direct causal link, whereby exposure to early stress disrupts biological functioning during sensitive periods of development; or (b) an indirect effect operating through socioeconomic attainment, poor health behaviors, or some other pathway leading from childhood to adulthood. The current study examined whether the association between childhood maltreatment and adult health reflects genetic or environmental mediation. Using a large sample of adult American twins, we separately estimated univariate biometric models of child maltreatment and adult physical health, followed by a bivariate biometric model to estimate genetic and environmental correlations between the two variables. We found that a summary count of chronic health conditions shared non-trivial genetic overlap with childhood maltreatment. Our results have implications for understanding the relationship between maltreatment and health as one of active interplay rather than a simple cause and effect model that views maltreatment as an exogenous shock.

Depressive vulnerability, stressful life events and episode onset of major depression: a longitudinal model

BACKGROUND

The nature of the relationship between depressive vulnerability (DV) and acute adversity in the etiology of major depression (MD) remains poorly understood.

METHOD

Stressful life events (SLEs) and MD onsets in the last year were assessed at four waves in cohort 1 (females) and at two waves in cohort 2 (males and females) from the Virginia Adult Twin Study. Structural equation modeling was conducted in Mplus.

RESULTS

In cohort 1, DV was strongly indexed by depressive episodes over the four waves (paths from +0.72 to 0.79) and predicted by SLEs in the month of their occurrence (+0.31 to 0.36). Wave-specific DV was associated both with stable DV (+0.29 to 0.33) and by forward transmission of DV from the preceding wave (+0.33 to 0.36). SLEs were predicted by stable DV (+0.29) and from SLEs in the preceding month (+0.06). As the cohort aged, MD onsets were better indexed by DV and more poorly predicted by SLEs. Parameter estimates were similar in males and females from cohort 2. In individuals with prior depressive episodes, the association between MD onset and SLEs was weakened while the prediction of SLEs from DV was substantially strengthened. We found no evidence for 'reverse causation' from MD episodes to SLEs.

CONCLUSION

The interrelationship between DV and acute adversity in the etiology of MD is complex and temporally dynamic. DV impacts on MD risk both directly and indirectly through selection into high stress environments. Over time, depressive episodes become more autonomous. Both DV and SLEs transmit forward over time and therefore form clear targets for intervention.

Association between stressful life events and psychotic experiences in adolescence: evidence for gene-environment correlations

BACKGROUND

Stressful life events (SLEs) are associated with psychotic experiences. SLEs might act as an environmental risk factor, but may also share a genetic propensity with psychotic experiences.

AIMS

To estimate the extent to which genetic and environmental factors influence the relationship between SLEs and psychotic experiences.

METHOD

Self- and parent reports from a community-based twin sample (4830 16-year-old pairs) were analysed using structural equation model fitting.

RESULTS

SLEs correlated with positive psychotic experiences (r = 0.12-0.14, all P<0.001). Modest heritability was shown for psychotic experiences (25-57%) and dependent SLEs (32%). Genetic influences explained the majority of the modest covariation between dependent SLEs and paranoia and cognitive disorganisation (bivariate heritabilities 74-86%). The relationship between SLEs and hallucinations and grandiosity was explained by both genetic and common environmental effects.

CONCLUSIONS

Further to dependent SLEs being an environmental risk factor, individuals may have an underlying genetic propensity increasing their risk of dependent SLEs and positive psychotic experiences.

Why some children with externalising problems develop internalising symptoms: testing two pathways in a genetically sensitive cohort study

BACKGROUND

Children with externalising problems are at risk of developing internalising problems as they grow older. The pathways underlying this developmental association remain to be elucidated. We tested two processes that could explain why some children with externalising problems develop internalising symptoms in preadolescence: a mediation model whereby the association between early externalising and later new internalising symptoms is explained by negative experiences; and a genetic model, whereby genes influence both problems.

METHODS

We used data from the Environmental Risk (E-Risk) Study, a 1994-1995 birth cohort of 2,232 twins born in England and Wales. We assessed externalising and internalising problems using combined mothers' and teachers' ratings at age 5 and 12. We measured bullying victimisation, maternal dissatisfaction and academic difficulties between age 7 and 10 and used linear regression analyses to test the effects of these negative experiences on the association between early externalising and later internalising problems. We employed a Cholesky decomposition to examine the genetic influences on the association.

RESULTS

Children with externalising problems at age 5 showed increased rates of new internalising problems at age 12 (r = .24, p < .001). Negative experiences accounted for some of the association between early externalising and later internalising problems. Behavioural-genetic analyses indicated that genes influencing early externalising problems also affected later internalising problems.

CONCLUSIONS

Our findings highlight the role of genetic influences in explaining why some children with externalising problems develop internalising symptoms in preadolescence. Negative experiences also contribute to the association, possibly through gene-environment interplay. Mental health professionals should monitor the development of internalising symptoms in young children with externalising problems.

A population-based longitudinal study of recent stressful life events as risk factors for suicidal behavior in major depressive disorder

The purpose of this study is to investigate whether the type and number of stressful life events (SLEs) will be associated with suicidal behavior in a 3-year follow-up period in persons with major depressive disorder (MDD). Data came from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), a nationally representative longitudinal survey of mental health in non-institutionalized adults in the United States. The survey consisted of two waves: Wave 1 (2001--2002) and Wave 2 (2004-2005), n = 34,653. Twelve past-year SLEs were assessed at baseline. These SLEs were categorized into the following groups based on previous research: Loss or victimization; Relationship, friendship, or interpersonal stress; Financial stress; and Legal problems. Only respondents with MDD at Wave 1 were included (n = 6,004). Several SLEs were strongly associated with suicide attempts, among which, "serious problems with neighbor, friend, or relative" (adjusted odds ratio [AOR] = 2.21; 95% confidence interval [95% CI]: 1.41, 3.45) and "major financial crisis, bankruptcy, or unable to pay bills" (AOR = 2.31; 95% CI: 1.45, 3.66) were the most robust predictors of suicide attempts even after adjusting for sociodemographic variables and any anxiety, substance use, or personality disorder. People with MDD who had been exposed to certain SLEs are at elevated risk for future suicide attempts, even after accounting for the demographic factors and psychiatric comorbidity.

Invited commentary on . . . Psychiatric resilience: longitudinal twin study

The study of resilience may lead to the identification of new targets for prevention and intervention, yet there has been little research on why some people, but not others, show resilience after facing stressful life events. New research in this issue shows that resilience is equally explained by genetic and environmental influences, and that individual experiences and situational factors are both important in shaping resilient responses to stress. These findings could inform the development of interventions that enhance psychiatric resilience after exposure to adversity.

Effect of OPRM1 and stressful life events on symptoms of major depression in African American adolescents

BACKGROUND

In a community sample of low-income African American adolescents, we tested the interactive effects of variation in the mu 1 opioid receptor (OPRM1) gene and the occurrence of stressful life events on symptoms of depression.

METHOD

Interactive effects of 24 OPRM1 simple nucleotide polymorphisms (SNP) and adolescent report of stressful life events on depression were tested using multilevel regressions. SNPs were dummy coded to test both additive and dominate forms of coding.

RESULTS

Five OPRM1 SNPs showed significant evidence of interaction with stressful life events to alter depression risk (or symptoms) after adjusting for multiple testing and the correlated nature of the SNPs. Follow-up analyses showed significant differences based on OPRM1 genotype at both lower and higher frequencies of stressful life events, suggesting that participants with a copy of the minor allele on OPRM1 SNPs rs524731, rs9478503, rs3778157, rs10485057, and rs511420 have fewer symptoms in low stress conditions but more symptoms in high stress conditions compared to major allele homozygotes.

LIMITATIONS

The genetic variants associated with depression in African American adolescents may not translate to other ethnic groups. This study is also limited in that only one gene that functions within a complex biological system is addressed.

CONCLUSIONS

This current study is the first to find an interaction between OPRM1 and life stress that is associated with depression. It also addressed an understudied population within the behavioral genetics literature. Further research should test additional genes involved in the opioid system and expand the current findings to more diverse samples.

Genome-wide association analysis accounting for environmental factors through propensity-score matching: application to stressful live events in major depressive disorder

Stressful life events are an established trigger for depression and may contribute to the heterogeneity within genome-wide association analyses. With depression cases showing an excess of exposure to stressful events compared to controls, there is difficulty in distinguishing between "true" cases and a "normal" response to a stressful environment. This potential contamination of cases, and that from genetically at risk controls that have not yet experienced environmental triggers for onset, may reduce the power of studies to detect causal variants. In the RADIANT sample of 3,690 European individuals, we used propensity score matching to pair cases and controls on exposure to stressful life events. In 805 case-control pairs matched on stressful life event, we tested the influence of 457,670 common genetic variants on the propensity to depression under comparable level of adversity with a sign test. While this analysis produced no significant findings after genome-wide correction for multiple testing, we outline a novel methodology and perspective for providing environmental context in genetic studies. We recommend contextualizing depression by incorporating environmental exposure into genome-wide analyses as a complementary approach to testing gene-environment interactions. Possible explanations for negative findings include a lack of statistical power due to small sample size and conditional effects, resulting from the low rate of adequate matching. Our findings underscore the importance of collecting information on environmental risk factors in studies of depression and other complex phenotypes, so that sufficient sample sizes are available to investigate their effect in genome-wide association analysis.

Estimating the heritability of reporting stressful life events captured by common genetic variants

BACKGROUND

Although usually thought of as external environmental stressors, a significant heritable component has been reported for measures of stressful life events (SLEs) in twin studies. Method We examined the variance in SLEs captured by common genetic variants from a genome-wide association study (GWAS) of 2578 individuals. Genome-wide complex trait analysis (GCTA) was used to estimate the phenotypic variance tagged by single nucleotide polymorphisms (SNPs). We also performed a GWAS on the number of SLEs, and looked at correlations between siblings.

RESULTS

A significant proportion of variance in SLEs was captured by SNPs (30%, p = 0.04). When events were divided into those considered to be dependent or independent, an equal amount of variance was explained for both. This 'heritability' was in part confounded by personality measures of neuroticism and psychoticism. A GWAS for the total number of SLEs revealed one SNP that reached genome-wide significance (p = 4 × 10-8), although this association was not replicated in separate samples. Using available sibling data for 744 individuals, we also found a significant positive correlation of R 2 = 0.08 in SLEs (p = 0.03).

CONCLUSIONS

These results provide independent validation from molecular data for the heritability of reporting environmental measures, and show that this heritability is in part due to both common variants and the confounding effect of personality.

Interaction between polygenic risk for cigarette use and environmental exposures in the Detroit Neighborhood Health Study

Cigarette smoking is influenced both by genetic and environmental factors. Until this year, all large-scale gene identification studies on smoking were conducted in populations of European ancestry. Consequently, the genetic architecture of smoking is not well described in other populations. Further, despite a rich epidemiologic literature focused on the social determinants of smoking, few studies have examined the moderation of genetic influences (for example, gene-environment interactions) on smoking in African Americans. In the Detroit Neighborhood Health Study (DNHS), a sample of randomly selected majority African American residents of Detroit, we constructed a genetic risk score (GRS), in which we combined top (P-value <5 × 10(-7)) genetic variants from a recent meta-analysis conducted in a large sample of African Americans. Using regression (effective n=399), we first tested for association between the GRS and cigarettes per day, attempting to replicate the findings from the meta-analysis. Second, we examined interactions with three social contexts that may moderate the genetic association with smoking: traumatic events, neighborhood social cohesion and neighborhood physical disorder. Among individuals who had ever smoked cigarettes, the GRS significantly predicted the number of cigarettes smoked per day and accounted for ~3% of the overall variance in the trait. Significant interactions were observed between the GRS and number of traumatic events experienced, as well as between the GRS and average neighborhood social cohesion; the association between genetic risk and smoking was greater among individuals who had experienced an increased number of traumatic events in their lifetimes, and diminished among individuals who lived in a neighborhood characterized by greater social cohesion. This study provides support for the utility of the GRS as an alternative approach to replication of common polygenic variation, and in gene-environment interaction, for smoking behaviors. In addition, this study indicates that environmental determinants have the potential to both exacerbate (traumatic events) and diminish (neighborhood social cohesion) genetic influences on smoking behaviors.

The effect of adolescent- and parent-induced family transitions in middle adolescence

In a longitudinal school-based survey of Finnish adolescents aged 15-16 years at baseline, we examined associations of parent-induced family transitions (parental separation, divorce, remarriage) and adolescent-induced family transitions (moving away from the parental home) with adolescent maladjustment (substance abuse and internalizing symptoms). The findings revealed that externalizing problems were associated with moving away from the parental home, whereas the risk of internalizing problems was associated with a change in the caretaking parent through parental marital transition or being taken into custody.