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This article reports results from the first twin study of adults in the United States that focuses exclusively and comprehensively on political traits. These data allow us to test whether a common set of genetic and environmental influences act upon a broad variety of values, personality traits, and political attitudes. In short, it allows us to empirically investigate whether there are a core set of predispositions that form the basis of our political orientations and, if so, whether these predispositions are shaped by the same environmental and innate forces. The key finding from our analysis is that there are core political predispositions that are rooted in common genetic and environmental influences and that these predispositions are empirically distinct from broader personality traits. [ABSTRACT FROM AUTHOR]

Background: A critical issue in devising effective interventions for the treatment of children's behavioral and emotional problems identifying genuine family environmental factors that place children at risk. In most twin and family studies, environmental factors are confounded with both direct genetic risk from parents and the indirect effect of genes influencing parents' ability to provide an optimal rearing environment. The present study was undertaken to determine whether parental psychopathology, specifically parental antisocial behavior (ASP), is a genuine environmental risk factor for juvenile conduct disturbance, depression and hyperactivity, or whether the association between parental ASP and children's behavioral and emotional problems can be explained as a secondary consequence of the intergenerational transmission of genetic factors. Methods: An extended children of twins design comprised of data collected on 2,674 adult female and male twins, their spouses, and 2,454 of their children was used to test whether genetic and/or family environmental factors best accounted for the association between parental antisocial behavior and children's behavioral problems. An age-matched sample of 2,826 juvenile twin pairs from the Virginia Twin Study of Adolescent Behavioral Development was also included to examine developmental differences in gene expression by partitioning child-specific transmissible effects from those effects that persist into adulthood. The fit of alternative models was evaluated using the statistical program Mx. Results: We found distinct patterns of transmission between parental antisocial behavior and juvenile conduct, depression and hyperactivity. Genetic and family environmental factors accounted for the resemblance between parents' ASP and children's conduct disturbance. Family environmental factors alone explained the association between child depression and parental ASP, and the impact of parental ASP on hyperactivity was entirely genetic. Conclusions: These findings underscore differences in the contribution of genetic and environmental factors on the patterns of association between parental antisocial behavior and juvenile psychopathology, having important clinical implications for the prevention and amelioration of child behavioral and emotional problems. [ABSTRACT FROM AUTHOR]

Ideological preferences within the American electorate are contingent on both the environmental conditions that provide the content of the contemporary political debate and internal predispositions that motivate people to hold liberal or conservative policy preferences. In this article we apply Jost, Federico, and Napier's top-down/bottom-up theory of political attitude formation to a genetically informative population sample. In doing so, we further develop the theory by operationalizing the top-down pathway to be a function of the social environment and the bottom-up pathway as a latent set of genetic factors. By merging insights from psychology, behavioral genetics, and political science, we find strong support for the top-down/bottom-up framework that segregates the two independent pathways in the formation of political attitudes and identifies a different pattern of relationships between political attitudes at each level of analysis. [ABSTRACT FROM AUTHOR]

Objectives Contemporary scholarly debate emphasizes the importance of spouse selection on population stratification, typically focusing on the traits of spouses themselves. In this study spouses and their parents were analyzed to resolve the effects of direct spousal assortment from family background assortment on three social traits that spouses correlate the highest: education, church attendance, and political affiliation. Methods The data set is comprised of a core of spousal pairs and their parents assessed by self-report and a more extensive set of individuals on whom there are only ratings by relatives for educational attainment, church attendance, and political preference. Structural equation models were fitted to the observed polychoric correlations by diagonal weighted least squares. Results For education and church attendance, assortment was based primarily on the traits of the spouses themselves, but models including independent assortment for the traits of parents-in-law gave a better fit. For political affiliation, assortment based on social background influenced by the traits of both parents gave a better fit. Conclusions The findings demonstrate that in humans, spousal similarity may reflect processes of selection and stratification that are more complex than commonly supposed in most models for family resemblance and social diversity. [ABSTRACT FROM AUTHOR]

Background: Despite the increased risk of depression and conduct problems in children of depressed parents, the mechanism by which parental depression affects their children’s behavioral and emotional functioning is not well understood. The present study was undertaken to determine whether parental depression represents a genuine environmental risk factor in children’s psychopathology, or whether children’s depression/conduct can be explained as a secondary consequence of the genetic liability transmitted from parents to their offspring. Methods: Children of Twins (COT) data collected on 2,674 adult female and male twins, their spouses, and 2,940 of their children were used to address whether genetic and/or family environmental factors best account for the association between depression in parents and depression and conduct problems in their children. Data collected on juvenile twins from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) were also included to estimate child-specific genetic and environmental influences apart from those effects arising from the transmission of the parental depression itself. The fit of alternative Children of Twin models were evaluated using the statistical program Mx. Results: The most compelling model for the association between parental and juvenile depression was a model of direct environmental risk. Both family environmental and genetic factors accounted for the association between parental depression and child conduct disturbance. Conclusions: These findings illustrate how a genetically mediated behavior such as parental depression can have both an environmental and genetic impact on children’s behavior. We find developmentally specific genetic factors underlying risk to juvenile and adult depression. A shared genetic liability influences both parental depression and juvenile conduct disturbance, implicating child conduct disturbance (CD) as an early indicator of genetic risk for depression in adulthood. In summary, our analyses demonstrate differences in the impact of parental depression on different forms of child psychopathology, and at various stages of development. [ABSTRACT FROM AUTHOR]

Background: If the adaptive significance of specific fears changes with age, the genetic contribution to individual differences may be lowest at the age of greatest salience. The roles of genes and environment in the developmental-genetic trajectory of five common childhood fears are explored in 1094 like-sex pairs of male and female monozygotic and dizygotic twins assessed on up to three occasions during adolescence (ages 8–18 years). Methods: Dichotomous self-ratings of a cluster of five correlated fears from Ollendick’s schedule of fears (FSSC-R) were extracted for subjects at each occasion of assessment. The effects of genes and environment on overall level of fears and rates of adolescent decline were explored by fitting an item-response theory (‘IRT’) model that allowed for individual genetic and environmental differences in initial fear level (‘intercept’) and rates of adolescent change (‘slope’) across the repeated waves of measurement. Different forms of the model were explored using Markov Chain Monte Carlo (MCMC) methods to derive the posterior distribution of subject and item parameters from the raw responses. Results: Additive genetic differences affect the common factor underlying the five fear-items. The same genes also affect rates of change with age, especially in boys. Male adolescents with higher overall genetic predisposition to childhood fears tended to show slower recovery with age than subjects with relatively low initial values. Thus, the genetic variance apparently increases with age. Conclusions: This finding is consistent with a prediction that the regulation of genetic differences will be strongest, and thus the additive genetic variance will be smallest, at the age when the particular stimulus is most salient. Items differed in the extent to which they were sensitive to underlying random differences in the rate of developmental change. Individual differences in rates of change with age were more marked in boys than girls. [ABSTRACT FROM AUTHOR]

Background: Although parental divorce is associated with increased substance use and internalizing problems, experiencing the separation of one's parents may not cause these outcomes. The relations may be due to genetic or environmental selection factors, characteristics that lead to both marital separation and offspring functioning. Method: We used the Children of Twins (CoT) Design to explore whether unmeasured genetic or environmental factors related to the twin parent, and measured characteristics of both parents, account for the association between parental divorce and offspring substance use and internalizing problems. Results: The association between parental divorce and offspring substance use problems remained robust when controlling for genetic and environmental risk from the twin parent associated with parental divorce, and measured characteristics of both parents. The results do not prove, but are consistent with, a causal connection. In contrast, the analyses suggest that shared genetic liability in parents and their offspring accounts for the increased risk of internalizing problems in adult offspring from divorced families. Conclusions: The study illustrates that unmeasured genetic and environmental selection factors must be considered when studying parental divorce. In explaining associations between parental divorce and young-adult adjustment, our evidence suggests that selection versus causal mechanisms may operate differently for substance abuse (a causal relation) and internalizing problems (an artifact of selection). The CoT design only controls for the genetic and environmental characteristics of one parent; thus, additional genetically informed analyses are needed. [ABSTRACT FROM AUTHOR]

In a wide variety of medical research scenarios one is interested in the question whether regression curves differ for subgroups in the sample. Examples are gender differences in the effect of drug treatment or the study of genotype-environment interactions. To address this question exploratory techniques are often required because detailed knowledge concerning the shape of the regression curves and how that shape differs across subgroups is lacking. In this article we explored the power of two such exploratory techniques: multivariate adaptive regression splines (MARS) and least squares curve fitting using polynomials. For this purpose simulations were performed using linear, logistic, and complex non-linear curves. The power obtained from MARS was on average 1.4 times higher than with polynomials. It was shown that power was higher even if the regression curve was linear, that gains increased with the complexity of the curve, and that for highly non-linear curves model-free methods such as MARS might be the only alternative. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recent reports using a classical behavior genetic research design in which twin data are combined with a measured characteristic of their shared family environment have made striking claims about estimating environmental influences on behavior with genetic effects controlled. Such claims are overstated for two related reasons. First, when a variable is measured at the family level in a way that makes it necessarily equivalent for twins reared together, it is not possible to partition it into genetic and environmental components. Second, although structural equation modeling and DeFries–Fulker analysis are sound tools for the analysis of many types of twin data, they do not control for genetic or environmental confounds when estimating the effect of measured family-level variables. [ABSTRACT FROM AUTHOR]

It is not known if the prevalence of parental psychiatric disorders is higher in stepfather than intact families, or if parental alcoholism is differentially associated with risk for conduct disorder (CD) symptoms in stepfather families versus intact families. The sample comprised 839 girls and 741 boys from 792 intact families and 99 girls and 67 boys from 83 stepfather families from a population-based registry of twins aged between 8 and 17 years. Children's current psychiatric symptoms were assessed at personal interview with the child, mother and father. Parental histories of psychiatric disorder were assessed at personal interview with each residential parent. Associations between CD symptoms and parental alcoholism were characterized using both linear and Poisson regression, and results are presented with and without adjustment for maternal drug use during pregnancy, parental conflict, and estimated socioeconomic status (SES) based on census tract data. Mothers from stepfather families had a higher lifetime prevalence of alcoholism, antisocial personality disorder, depression and social phobia than mothers from intact families. Stepfathers had a higher lifetime prevalence of alcoholism and depression than biological fathers from intact families. Children from stepfather families had more externalizing (CD/ODD) symptoms than children from intact families. Girls who lived with an alcoholic stepfather had significantly more CD symptoms than girls who lived with an alcoholic biological father. Boys who lived with an alcoholic stepfather had significantly fewer CD symptoms than boys who lived with an alcoholic biological father. This sex difference was statistically significant. Adjustment for maternal drug use during pregnancy, parental conflict, and estimated SES based on census tract data did not change these findings. Children living in stepfather families are exposed to more parental psychiatric risk factors than children from intact families. The increased risk for CD symptoms in girls (but not boys) from stepfather families is partly mediated by or associated with the stepfather's history of alcoholism. [ABSTRACT FROM AUTHOR]

Background: Determination of causal connections between parental measures and child outcomes using typical samples is limited by the inability to account for all confounds, both environmental and genetic. This paper discusses the strength of the Children of Twins (COT) design to highlight the role of specific environments. Methods: A new analytical model is presented which helps differentiate and quantify the environmental and genetic processes underlying associations between family-level risk factors and child adjustment. In order to illustrate the COT design, the relation between smoking during pregnancy and child birth weight (BW) is examined in a sample of female twins and their children from Norway and the United States. Results: The results illustrate that smoking during pregnancy is influenced by genetic factors. However, the Children of Twins model supports the claim that smoking during pregnancy has a direct environmental influence on BW and that genetic and shared environmental confounds cannot account for the association. Conclusions: An assessment of the strengths and limitations of the Children of Twins design and a comparison with other research strategies suggest that the design plays a unique role in the study of developmental psychology and psychopathology. Finally, the authors describe how methodological advances and future applications of the design will provide additional insight into the causal processes underlying children's adjustment to environmental stimuli. [ABSTRACT FROM AUTHOR]

Background: The aim was to compare the psychometric properties of absolute versus differential ratings of the within-family environments and to examine their associations with conduct problems in 8-16-year-old twins. Methods: The sample comprised 1117 pairs of like-sex male and female twins and their parents, recruited from the school population of Virginia. The within-family environment was assessed from the Twin Inventory of Relationships and Experiences (TIRE), which provided measures of differential parental criticism, parental preference for one twin, and twins' peers' conduct problems, as rated by mothers, fathers and each of the twins. Twins' conduct problems were assessed by a modified version of the Olweus questionnaire. Results: Although differential ratings and absolute ratings had similar psychometric properties, the use of absolute ratings to differentiate the twins resulted in a construct with weak inter-rater agreement and low stability over time. Differential ratings of the twins' environment showed significant associations with differences in conduct problems between the twins, whereas the difference in absolute ratings of each twin did not. The differential parental criticism effect was uninfluenced by the overall level of criticism in the family. Conclusions: A direct contrast between siblings or twins, as part of the rating procedure (as provided by differential ratings), may be a more efficient way to assess aspects of the within-family environment that are reliable and which are associated with psychopathology. Both differential parental criticism and peers' conduct disturbance were associated with conduct problems in the twins. TIRE: Twin Inventory of Relationships and Experiences; VTSABD: Virginia Twin Study of Adolescent Behavioral Development [ABSTRACT FROM AUTHOR]

The phenotypic and genetic interrelationships underlying ADHD symptomatology assessed by various instruments were examined on a sample of 735 male and 819 female same-sex twin pairs, aged 8 to 16 years, participating in the first phase of the Virginia Twin Study of Adolescent Behavioral Development (VTSABD). Multivariate analyses were applied to parental and teacher ratings from an investigator-based interview, the CAPA, and three questionnaires (the CBCL and the Rutter Parent and Teacher Scales). Results from patterns of intercorrelations and factor analyses of maternal measures suggested that at the phenotypic level, these assessed the same underlying behavioural construct, which differed from other emotional and behavioural constructs. However, genetic analyses showed that in addition to a common factor underlying the expression of ADHD as assessed across the range of measures, additional genetic factors were identified that were method- and rater-specific. The findings suggest that although the investigator-based interview and the behavioural checklists tap similar aspects of ADHD behaviour, there is additional rater-specific variance. [ABSTRACT FROM AUTHOR]

In this report we characterize associations between parental psychiatric disorders and children's psychiatric symptoms and disorders using a population-based sample of 850 twin families. Juvenile twins are aged 8-17 years and are personally interviewed about their current history of DSM-III-R conduct, depression, oppositional-defiant, overanxious, and separation anxiety disorders using the CAPA-C. Mothers and fathers of twins are personally interviewed about their lifetime history of DSM-III-R alcoholism, antisocial personality disorder, generalized anxiety disorder, major depression, panic disorder/agoraphobia, social phobia, and simple phobia using a modified version of the SCID and the DIS. Generalized least squares and logistic regression are used to identify the juvenile symptoms and disorders that are significantly associated with parental psychiatric histories. The specificity of these associations is subsequently explored in a subset of families with maternal, plus parental psychiatric histories with a prevalence > 1%. Parental depression that is not comorbid or associated with a different spousal disorder is associated with a significantly elevated level of depression and overanxious disorder symptoms and a significantly increased risk for overanxious disorder. Risks are higher for both symptomatic domains in association with maternal than paternal depression, and highest in association with maternal plus paternal depression. Risks for other juvenile symptoms and disorders index the comorbid and spousal histories with which parental depression is commonly associated. Paternal alcoholism that is not comorbid or associated with a maternal disorder is not significantly associated with current psychiatric symptoms or disorders in offspring. Risks for oppositional-defiant or conduct symptoms/disorders in the offspring of alcoholic parents index parental comorbidity and/or other spousal histories. [ABSTRACT FROM AUTHOR]

Although the transmission of religiousness has been assumed to be purely cultural, behavior genetic studies have demonstrated that genetic factors play a role in the individual differences in some religious traits. This article reviews the extant behavior genetic literature and presents new analyses from the "Virginia 30,000" on the causes of variation in religious affiliation, attitudes, and practices, and relates these to personality as construed by Eysenck. Results indicate that religious affiliation is primarily a culturally transmitted phenomenon, whereas religious attitudes and practices are moderately influenced by genetic factors. Further, Eysenck's personality traits do not mediate genetic influences on religiousness, but significant negative genetic correlations are found between church attendance and liberal sexual attitudes. Implications and possibilities for future studies are discussed. [ABSTRACT FROM AUTHOR]

Little is known about the contribution of genetic and environmental factors to risk for juvenile psychopathology. The Virginia Twin Study of Adolescent Behavioral Development allows these contributions to be estimated. A population-based, unselected sample of 1412 Caucasian twin pairs aged 8-16 years was ascertained through Virginia schools. Assessment of the children involved semi-structured face-to-face interviews with both twins and both parents using the Child and Adolescent Psychiatric Assessment (CAPA). Self-report questionnaires were also completed by parents, children, and teachers. Measures assessed DSM-III-R symptoms of Attention Deficit Hyperactivity Disorder (ADHD), Conduct Disorder, Oppositional Defiant Disorder, Overanxious Disorder, Separation Anxiety, and Depressive Disorder. Factorially derived questionnaire scales were also extracted. Scores were normalized and standardized by age and sex. Maximum likelihood methods were used to estimate contributions of additive and nonadditive genetic effects, the shared and unique environment, and sibling imitation or contrast effects. Estimates were tested for heterogeneity over sexes. Generally, monozygotic (MZ) twins correlated more highly than dizygotic (DZ) twins, parental ratings more than child ratings, and questionnaire scales more highly than interviews. DZ correlations were very low for measures of ADHD and DZ variances were greater than MZ variances for these variables. Correlations sometimes differed between sexes but those for boy-girl pairs were usually similar to those for like-sex pairs. Most of the measures showed small to moderate additive genetic effects and moderate to large effects of the unique individual environment. Measures of ADHD and related constructs showed marked sibling contrast effects. Some measures of oppositional behavior and conduct disorder showed shared environmental effects. There were marked sex differences in the genetic contribution to separation anxiety, otherwise similar genetic effects appear to be expressed in boys and girls. Effects of rater biases on the genetic analysis are considered. The study supports a widespread influence of genetic factors on risk to adolescent psychopathology and suggests that the contribution of different types of social influence may vary consistently across domains of measurement. [ABSTRACT FROM AUTHOR]

The authors seek to determine whether the clinical characteristics of generalized anxiety disorder (GAD) differ in individuals with a high vs. low familial vulnerability to illness. We identified 486 personally interviewed female twins front a population-based register who had both an interviewed co-twin and a lifetime history of GAD using modified DSM-III-R criteria which required a one-month minimum duration of illness. We attempted to predict risk for GAD in the co-twin from the clinical features of the GAD in the prohand twin using the Cox proportional hazard model, controlling for year of birth and zygosity. Only two variables uniquely predicted an increased risk for GAD in the co-twin: number of GAD symptoms endorsed and comorbidity with bulimia. Variables that did not uniquely predict risk of illness in the co-twin included age at onset, duration of the longest episode and number of episodes. The familial vulnerability to GAD can be meaningfully indexed by clinical features of the syndrome. These results suggest that if the syndrome of GAD is to be narrowed, it would, from a familial perspective, be more valid to increase the minimum number of required symptoms rather than to increase the minimum duration of illness. [ABSTRACT FROM AUTHOR]

We introduce an overlapping cohort sequential longitudinal study of behavioral development and psychopathology in a representative sample of 1412 pairs of twins aged 8 through 16 years. Multiple phenotypic assessments involve a full psychiatric interview with each child and each parent, and supplementary parental, teacher, and child interview material and questionnaires. For the first wave of assessments, the numbers of reported DSM-III-R symptoms of Major Depressive Disorder (MDD), Separation Anxiety Disorder (SAD), Overanxious Disorder (OAD), Oppositional Defiant Disorder (ODD), Conduct Disorder (CD), and Attention Deficit Hyperactivity Disorder (ADHD), assessed through interviews, confirm patterns of age and sex trends found in other epidemiological samples, but underscore their dependence on whether the child or the parent is the informant. Correlations across domains for symptoms reported by the same informant are often as large as correlations across informants for the same domain of symptoms. Factor analyses of these symptom counts, taking account of informant view and unreliability of assessment, show the high degree of correlation between SAD and OAD, between MDD and OAD, and between CD and ODD. ADHD symptoms are relatively independent of the other domains, but show moderate correlations with CD, ODD, and MDD. Factorially derived dimensional questionnaire scales, based on child, parental, and teacher reports, show patterns of relationship to symptom counts consistent with both convergent and discriminant validity as indices of liability to clinical symptoms. Across informants, questionnaire scales provide as good a prediction of symptoms as do clinical interviews. Multitrait-multimethod confirmatory factor analysis reveals the patterns of relationship between symptoms of psychiatric disorder in children taking due account of informant and unique sources of variance. Gender differences are consistent within the correlated clusters of ODD/CD and MDD/SAD/OAD, although there are disorder-specific age trends. There are large informant-specific influences on the reporting of symptoms in clinical interviews. Dimensional questionnaire scales provide a useful source of additional information. In subsequent analyses of genetic and environmental etiology of childhood psychopathology we must expect that results may differ by informant and method of assessment. Multivariate and developmental analyses that explore the sources of these differences will shed new light on the relationship between genetic and environmentally influenced vulnerability and the manifestation of psychopathology in specific circumstances. [ABSTRACT FROM AUTHOR]

Measures of reading achievement and verbal ability have been shown to be heritable. Additionally, recent evidence has been suggestive of a major gene effect on reading disability and for problem reading in a sample of normal readers. We report on the etiology of individual differences in oral reading performance, the Slosson Oral Reading Test (SORT), for which biometrical analyses have not been reported in the literature previously. Oral reading performance was measured in a large population-based sample of twins of the Virginia Twin Study of Adolescent Behavioral Development. Biometrical analyses of the SORT suggested that, in both mates and females. 69% of the phenotypic variation was due to heritable influences and 13'v of the variation dm- to shared environmental effects. While the relative importance of genetic and environmental influences is equivalent for males and females, males showed greater phenotypic variability than females. [ABSTRACT FROM AUTHOR]

There has been recent interest in the possibility of dividing bulimia nervosa into two sub- types based on the method of weight prevention utilized by the individual. In an attempt to see if such division is justified, this study, compared 54 purging bulimics with G9 nonpurging bulimics ascertained from a population-based register of Virginia female twins. A bulimic was defined as a ‘purger’ if she engaged in vomiting or laxativee abuse. These two groups were examined on a variety of demographic, weight, and personality measures after controlling for the presence of obesity. No significant differences were found between the two groups on any of the variables examined. [ABSTRACT FROM AUTHOR]

Height was measured in a health screening of the population in Nord-Trøndelag, Norway. Correlations were computed for 24,281 pairs of spouses, 43,613 pairs of parents and offspring, 19,168 pairs of siblings, 1,318 pairs of grandparents and grandchildren, 1,218 cognate avuncular pairs, 849 noncognate avuncular pairs, 175 pairs of same-sexed twins, and smaller groups of other types of relatives. Fitting of structural equation models showed proportions of additive genetic variance of approximately 0.8 for both sexes and small sex-specific effects that probably reflect genetic dominance or environmental sibling effects. The correlations between parents and offspring were significantly lower in old than young cohorts, seeming to imply some kind of interaction effect between genes and environment. © 1992 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The reported interaction between the length polymorphism (5HTTLPR) in the serotonin transporter gene (SLC6A4) and stressful life events on depression has led to many attempts to replicate but with inconsistent results. This inconsistency may reflect, in part, small sample size and the unknown contribution of the long allele SNP, rs25531. Using a large twin sample of 3,243 individuals from 2,230 families aged 18-95 years (mean = 32.3, SD = 13.6) we investigate the interaction between 5HTTLPR (subtyped with SNP rs25531) and stressful events on risk of depression and suicidality using both ordinal regressions and item response theory analyses. Participants reported via mailed questionnaire (82% response rate) both stressful events in the preceeding 12 months and symptoms of depression. Stressful events were defined as "personal" (affecting the individual), or "network" (affecting close family or friends). One to 10 years later (mean = 4.2 years), participants completed a comprehensive clinical psychiatric telephone interview (83% response rate) which assessed DSM-IV major depression and ideation of suicidality. Self-reports of depression and an increase in depression/suicidality assessed by clinical interview are significantly associated with prior personal events (P < 0.001) after controlling for age and sex. However, they are inconsistently associated with prior network events (ranging, ns to P < 0.01) and are not significantly associated with any of the genotype main effects (5HTTLPR, 5HTTLPR + rs25531) or interactions (stress x genotype). We find no evidence to support the hypothesis of any 5HTTLPR genotype by stress interaction.