Espen Røysamb

The Structure of Genetic and Environmental Risk Factors for Syndromal and Subsyndromal Common DSM-IV Axis I and All Axis II Disorders

OBJECTIVE The authors sought to clarify the structure of the genetic and environmental risk factors for 22 DSM-IV disorders: 12 common axis I disorders and all 10 axis II disorders. METHOD The authors examined syndromal and subsyndromal axis I diagnoses and five categories reflecting number of endorsed criteria for axis II disorders in 2,111 personally interviewed young adult members of the Norwegian Institute of Public Health Twin Panel. RESULTS Four correlated genetic factors were identified: axis I internalizing, axis II internalizing, axis I externalizing, and axis II externalizing. Factors 1 and 2 and factors 3 and 4 were moderately correlated, supporting the importance of the internalizing-externalizing distinction. Five disorders had substantial loadings on two factors: borderline personality disorder (factors 3 and 4), somatoform disorder (factors 1 and 2), paranoid and dependent personality disorders (factors 2 and 4), and eating disorders (factors 1 and 4). Three correlated environmental factors were identified: axis II disorders, axis I internalizing disorders, and externalizing disorders versus anxiety disorders. CONCLUSIONS Common axis I and II psychiatric disorders have a coherent underlying genetic structure that reflects two major dimensions: internalizing versus externalizing, and axis I versus axis II. The underlying structure of environmental influences is quite different. The organization of common psychiatric disorders into coherent groups results largely from genetic, not environmental, factors. These results should be interpreted in the context of unavoidable limitations of current statistical methods applied to this number of diagnostic categories.

Perceived difficulty in the theory of planned behaviour: perceived behavioural control or affective attitude?

A study was conducted to explore (a) the dimensional structure of perceived behavioural control (PBC), (b) the conceptual basis of perceived difficulty items, and (c) how PBC components and instrumental and affective attitudes, respectively, relate to intention and behaviour. The material stemmed from a two-wave study of Norwegian graduate students (N = 227 for the prediction of intention and N = 110 for the prediction of behaviour). Data were analysed using confirmatory factor analysis (CFA) and multiple regression by the application of structural equation modelling (SEM). CFA suggested that PBC could be conceived of as consisting of three separate but interrelated factors (perceived control, perceived confidence and perceived difficulty), or as two separate but interrelated factors representing self-efficacy (measured by perceived difficulty and perceived confidence or by just perceived confidence) and perceived control. However, the perceived difficulty items also overlapped substantially with affective attitude. Perceived confidence was a strong predictor of exercise intention but not of recycling intention. Perceived control, however, was a strong predictor of recycling intention but not exercise intention. Affective attitudes but not instrumental attitudes were identified as substantial predictors of intentions. The findings suggest that at least under some circumstances it may be inadequate to measure PBC by means of perceived difficulty. One possible consequence may be that the role of PBC as a predictor of intention is somewhat overestimated, whereas the role of (affective) attitude may be similarly underestimated.

The Structure of Genetic and Environmental Risk Factors for DSM-IV Personality Disorders: A Multivariate Twin Study

CONTEXT Although both genetic and environmental factors affect risk of individual personality disorders (PDs), we know little of how they contribute to the pattern of comorbidity between the PDs in the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) (DSM-IV). OBJECTIVE To clarify the structure of the genetic and environmental risk factors for the 10 DSM-IV PDs. DESIGN Assessment of PDs at personal interview and multivariate twin modeling with the Mx program. SETTING General community. PARTICIPANTS A total of 2794 young adult members of the Norwegian Institute of Public Health Twin Panel. Main Outcome Measure Number of endorsed criteria for the 10 DSM-IV PDs. RESULTS The best-fit multivariate twin model required 3 genetic and 3 individual-specific environmental factors and genetic and individual-specific factors unique to each PD. The first genetic factor had high loadings on PDs from all 3 clusters including paranoid, histrionic, borderline, narcissistic, dependent, and obsessive-compulsive. The second genetic factor had substantial loadings only on borderline and antisocial PD. The third genetic factor had high loadings only on schizoid and avoidant PD. Several PDs had substantial disorder-specific genetic risk factors. The first, second, and third individual-specific environmental factors had high loadings on the cluster B, A, and C PDs, respectively, with 1 exception: obsessive-compulsive PD loaded with cluster B and not cluster C PDs. CONCLUSIONS Genetic risk factors for DSM-IV PDs do not reflect the cluster A, B, and C typology. Rather, 1 genetic factor reflects a broad vulnerability to PD pathology and/or negative emotionality. The 2 other genetic factors are more specific and reflect high impulsivity/low agreeableness and introversion. Unexpectedly, the cluster A, B, and C typology is well reflected in the structure of environmental risk factors, suggesting that environmental experiences may be responsible for the tendency of cluster A, B, and C PDs to co-occur.

The effect of acculturation and social support on change in mental health among young immigrants

The aim of the study was to examine the mediating and moderating roles of social support in the acculturation–mental health link, and to investigate how these processes combine with self-esteem to affect mental health change. Questionnaire data were collected twice from 137 immigrant students, first at the upstart in junior high school, and then again a year later (8th and 9th grade). Acculturation was described in positive terms as a developmental process towards gaining competence within more than one sociocultural setting. Perceived discrimination and ethnic identity crisis were included as risk factors in this process. A model of structural relations was tested, which after some modifications demonstrated a close fit to the data. The results supported our suggestions of two indirect paths of effects of acculturation on mental health change: one through culture domain-specific social support and another through self-esteem. Self-esteem was also identified as a mediator of identity crisis. Significant interaction effects between social support and culture competencies were demonstrated in addition to buffer effects of class and family support in relation to identity crisis and discrimination respectively. The study adds to our understanding of positive and negative developmental pathways in multicultural societies.

Subjective well-being : genetic and environmental contributions to stability and change

BACKGROUND Previous cross-sectional studies have found substantial genetic influences on individual variation in subjective well-being (SWB), and evidence for sex-specific genetic effects has been reported. However, the genetic and environmental influences on stability and change in SWB over time are largely unexplored. METHOD Questionnaire data on SWB from a population-based sample of Norwegian twins born 1967 to 1979, initially surveyed in 1992 (T1) and re-surveyed in 1998 (T2), were analysed using structural equation modelling to explore the relative effects of genetic and environmental influences on phenotypic stability and change. RESULTS The phenotypic cross-time correlations for SWB were 0.51 and 0.49 for males and females respectively. The best-fitting longitudinal model specified only additive genetic and individual environmental effects with qualitative and quantitative sex-specific genetic influences. For both males and females, the additive genetic factors influencing SWB were largely stable, although some time-specific genetic contributions were indicated. Cross-time correlations for genetic effects were 0.85 and 0.78 for males and females respectively. The individual environmental influences were primarily time-specific. Additive genetic effects explained approximately 80% of the phenotypic cross-time correlation. For females, the magnitude of the additive genetic effects decreased significantly from T1 to T2, whereas for males, the estimates generally remained unchanged. CONCLUSIONS For both males and females, long-term stability of SWB was mainly attributable to stable additive genetic factors, whereas susceptibility to change was mostly related to individual environmental factors. However, both stable environmental contributions and emerging genetic influences were indicated.

Attrition and generalizability in longitudinal studies: findings from a 15-year population-based study and a Monte Carlo simulation study

BackgroundAttrition is one of the major methodological problems in longitudinal studies. It can deteriorate generalizability of findings if participants who stay in a study differ from those who drop out. The aim of this study was to examine the degree to which attrition leads to biased estimates of means of variables and associations between them.MethodsMothers of 18-month-old children were enrolled in a population-based study in 1993 (N=913) that aimed to examine development in children and their families in the general population. Fifteen years later, 56% of the sample had dropped out. The present study examined predictors of attrition as well as baseline associations between variables among those who stayed and those who dropped out of that study. A Monte Carlo simulation study was also performed.ResultsThose who had dropped out of the study over 15 years had lower educational level at baseline than those who stayed, but they did not differ regarding baseline psychological and relationship variables. Baseline correlations were the same among those who stayed and those who later dropped out. The simulation study showed that estimates of means became biased even at low attrition rates and only weak dependency between attrition and follow-up variables. Estimates of associations between variables became biased only when attrition was dependent on both baseline and follow-up variables. Attrition rate did not affect estimates of associations between variables.ConclusionsLong-term longitudinal studies are valuable for studying associations between risk/protective factors and health outcomes even considering substantial attrition rates.

Happiness and Health: Environmental and Genetic Contributions to the Relationship Between Subjective Well-Being, Perceived Health, and Somatic Illness

The aim was to identify genetic and environmental influences on the covariances between subjective well-being (SWB), perceived health, and somatic illness. Analyses were based on 6576 Norwegian twins aged 18-31. Heritabilities ranged from .24 to.66. SWB correlated .50 with perceived health, -.25 with musculoskeletal pain, and -.07 with allergy. Common genetic factors accounted for 45%-60% of associations. SWB and perceived health was to a high extent influenced by the same genes (r(g)=.72 and.82 for males and females, respectively). For SWB and musculoskeletal pain, r-sub(g) =-.29 and -.42 for males and females, respectively. Effects were partly sex specific. Environmental factors shared by twins did not affect the covariances. Results support a differentiated view of SWB-health relations, and imply that both genes and environment play important roles in the associations between well-being and health.

Subjective well-being. Sex-specific effects of genetic and environmental factors

Genetic and environmental factors in subjective well-being were investigated. Special attention was paid to sex-specific effects. A classical twin design was applied, based upon data from 5140 young adult twins (same and opposite-sex). Structural equation modelling was used to estimate effects from additive genes, genetic interaction, common environment and non-shared environment. The best fitting model involved an additive genetic factor and non-shared environment. There were only marginal sex differences in mean levels of subjective well-being, and no differences in variance. Yet, there were sex differences in the degree of heritability (0.54 for women and 0.46 for men). Additionally, the correlation between the male and female genetic factors was 0.64, suggesting that, in part, different sets of genes may influence variation in subjective well-being for men and women. A dual mechanism process of genetic influence upon well-being is proposed, comprising the notion of interaction between genotypes and cultural value systems.

The Joint Structure of DSM–IV Axis I and Axis II Disorders

The Diagnostic and Statistical Manual (4th ed. [DSM-IV]; American Psychiatric Association, 1994) distinction between clinical disorders on Axis I and personality disorders on Axis II has become increasingly controversial. Although substantial comorbidity between axes has been demonstrated, the structure of the liability factors underlying these two groups of disorders is poorly understood. The aim of this study was to determine the latent factor structure of a broad set of common Axis I disorders and all Axis II personality disorders and thereby to identify clusters of disorders and account for comorbidity within and between axes. Data were collected in Norway, through a population-based interview study (N = 2,794 young adult twins). Axis I and Axis II disorders were assessed with the Composite International Diagnostic Interview (CIDI) and the Structured Interview for DSM-IV Personality (SIDP-IV), respectively. Exploratory and confirmatory factor analyses were used to investigate the underlying structure of 25 disorders. A four-factor model fit the data well, suggesting a distinction between clinical and personality disorders as well as a distinction between broad groups of internalizing and externalizing disorders. The location of some disorders was not consistent with the DSM-IV classification; antisocial personality disorder belonged primarily to the Axis I externalizing spectrum, dysthymia appeared as a personality disorder, and borderline personality disorder appeared in an interspectral position. The findings have implications for a meta-structure for the DSM.

Multivariate genetic analysis of sex limitation and G x E interaction.

Sex-limited expression of genetic or environmental factors occurs in two basic forms. First, the effects of a factor may be larger on one sex than on another, which is known as scalar sex limitation. Second, some factors may have an effect on one sex but not on the other, which is called nonscalar sex limitation. In the classical twin study, scalar sex-limited effects cause same-sex male and same-sex female twin correlations to differ. Nonscalar sex-limited effects would cause the correlations between opposite-sex pairs of relatives to be lower than would be expected from the correlations between relatives of the same sex. One approach to modeling such effects is to allow the genetic correlation between opposite-sex dizygotic twins to be less than one-half; another is to allow the common environment correlation for opposite-sex pairs to be less than unity. Extension of this approach to the multivariate case is not straightforward. Direct extension of the Cholesky decomposition such that each Cholesky factor is allowed to correlate less than one-half in opposite-sex pairs yields a model where the order of the variables can change the goodness-of-fit of the model. It is shown that similar problems exist with a variety of multivariate and longitudinal models, and in a variety of models of genotype x environment interaction. Several solutions to these problems are described.