A psychometric evaluation of the DSM-IV borderline personality disorder criteria: age and sex moderation of criterion functioning

BACKGROUND

Despite its importance as a paradigmatic personality disorder, little is known about the measurement invariance of the DSM-IV borderline personality disorder (BPD) criteria; that is, whether the criteria assess the disorder equivalently across different groups.

METHOD

BPD criteria were evaluated at interview in 2794 young adult Norwegian twins. Analyses, based on item-response modeling, were conducted to test for differential age and sex moderation of the individual BPD criteria characteristics given factor-level covariate effects.

RESULTS

Confirmatory factor analytic results supported a unidimensional structure for the nine BPD criteria. Compared to males, females had a higher BPD factor mean, larger factor variance and there was a significant age by sex interaction on the factor mean. Strong differential sex and age by sex interaction effects were found for the 'impulsivity' criterion factor loading and threshold. Impulsivity related to the BPD factor poorly in young females but improved significantly in older females. Males reported more impulsivity compared to females and this difference increased with age. The 'affective instability' threshold was also moderated, with males reporting less than expected.

CONCLUSIONS

The results suggest the DSM-IV BPD 'impulsivity' and 'affective instability' criteria function differentially with respect to age and sex, with impulsivity being especially problematic. If verified, these findings have important implications for the interpretation of prior research with these criteria. These non-invariant age and sex effects may be identifying criteria-level expression features relevant to BPD nosology and etiology. Criterion functioning assessed using modern psychometric methods should be considered in the development of DSM-V.

Genetisk epidemiologiske studier av psykiatriske lidelser

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Structure of genetic and environmental risk factors for dimensional representations of DSM-IV anxiety disorders

BACKGROUND

Twin data permit decomposition of comorbidity into genetically and environmentally derived correlations. No previous twin study includes all major forms of anxiety disorder.

AIMS

To estimate the degree to which genetic and environmental risk factors are shared rather than unique to dimensionally scored panic disorder, generalised anxiety disorder, phobias, obsessive-compulsive disorder and post-traumatic stress disorder.

METHOD

Data obtained from 2801 young-adult Norwegian twins by means of the Composite International Diagnostic Interview were analysed with the Mx program.

RESULTS

A multivariate common factor model fitted best. The latent liability to all anxiety disorders was substantially more heritable (54%) than the individual disorders (23% to 40%). Most of the genetic effect was common to the disorders. Genes contributed just over 50% to the covariance between liabilities.

CONCLUSIONS

The five anxiety disorders all share genetic and environmental risk factors. This has implications for the revision of the anxiety disorder section in DSM-V.

Attitudes toward weight gain during pregnancy: results from the Norwegian mother and child cohort study (MoBa)

OBJECTIVE

To explore attitudes toward weight gain during pregnancy in women with and without eating disorders and across eating disorder subtypes, and to examine associations among weight-gain attitudes and actual gestational weight gain, infant birth weight, and infant size-for-gestational-age.

METHOD

Pregnant women (35,929) enrolled in the prospective population-based Norwegian mother and child cohort study (MoBa) provided information at approximately week 18 of gestation regarding eating disorders and weight gain attitudes. We explored these variables in women with anorexia nervosa, bulimia nervosa, eating disorder not otherwise specified, purging type, and binge eating disorder (BED).

RESULTS

The presence of an eating disorderly was associated with greater worry over gestational weight gain. In women without eating disorders, greater worry was associated with higher gestational weight gain, higher infant weights, greater likelihood of a large-for-gestational-age infant, and reduced likelihood of a small-for-gestational-age infant. Women with BED who reported greater worry also experienced higher weight gains during pregnancy.

DISCUSSION

Women with eating disorders tend to experience weight-gain-related worry during pregnancy. Early worry about gestational weight-gain may be a harbinger of high gestational gain.

The Norwegian Institute of Public Health twin study of mental health: examining recruitment and attrition bias

All Norwegian twin pairs born 1967-1974 and still living in Norway in 1992 were invited to a health questionnaire study (Q1). 2,570 pairs (65%) participated. These cohorts and the twin cohorts born 1967-1979 were invited to a new questionnaire study (Q2) in 1998. This time 3,334 pairs (53%) participated. Almost all pairs having participated in the 1998 study were invited to an interview study of mental health (MHS), taking place 1999-2004. 1,391 complete pairs (44%) participated. The questionnaire studies included extensive data on somatic health with fewer items on mental health and demography. Health-related and demographic information available from the Medical Birth Registry on all invited twins was applied to predict participation to the first study. A few registry variables indicating poor health predicted nonparticipation in Q1. Health information and demography from Q1 were tested as predictors of participation in the follow-up study (Q2). Monozygosity, female sex, being unmarried, having no children, and high education predicted participation, whereas few indicators of poor mental and somatic health and unhealthy lifestyle moderately predicted nonparticipation in Q2. No health indicators reported in Q2 predicted further participation. Standard genetic twin analyses of indicators of various mental disorders from Q2, validated by diagnostic data from the MHS, did not indicate differences in genetic/environmental covariance structures between participants and nonparticipants in MHS. In general the results show a moderate selection towards good mental and somatic health. Attrition from Q2 to the MHS does not appear to affect twin analyses of mental health related variables.

Assessing the heritability of anorexia nervosa symptoms using a marginal maximal likelihood approach

BACKGROUND

Assessment of eating disorders at the symptom level can facilitate the refinement of phenotypes. We examined genetic and environmental contributions to liability to anorexia nervosa (AN) symptoms in a population-based twin sample using a genetic common pathway model.

METHOD

Participants were from the Norwegian Institute of Public Health Twin Panel (NIPHTP) and included all female monozygotic (MZ; 448 complete pairs and four singletons) and dizygotic (DZ; 263 complete pairs and four singletons) twins who completed the Composite International Diagnostic Interview (CIDI) assessing DSM-IV Axis I and ICD-10 criteria. Responses to items assessing AN symptoms were included in a model fitted using the marginal maximum likelihood (MML) approach.

RESULTS

Heritability of the overall AN diagnosis was moderate [a2=0.22, 95% confidence interval (CI) 0.0-0.50] whereas heritabilities of the specific items varied. Heritability estimates for weight loss items were moderate (a2=0.31-0.34) and items assessing weight concern when at a low weight were smaller (0.18-0.29). Additive genetic factors contributed little to the variance of amenorrhea, which was most strongly influenced by unshared environment (a2=0.16, e2=0.71).

CONCLUSIONS

AN symptoms are differentially heritable. Specific criteria such as those related to body weight and weight loss history represent more biologically driven potential endophenotypes or liability indices. The results regarding weight concern differ somewhat from those of previous studies, highlighting the importance of assessing genetic and environmental influences on variance of traits within specific subgroups of interest.

Birth outcomes in women with eating disorders in the Norwegian Mother and Child cohort study (MoBa)

OBJECTIVE

We explored the impact of eating disorders on birth outcomes in the Norwegian Mother and Child Cohort Study.

METHOD

Of 35,929 pregnant women, 35 reported broad anorexia nervosa (AN), 304 bulimia nervosa (BN), 1,812 binge eating disorder (BED), and 36 EDNOS-purging type (EDNOS-P) in the six months before or during pregnancy. The referent comprised 33,742 women with no eating disorder.

RESULTS

Pre-pregnancy body mass index (BMI) was lower in AN and higher in BED than the referent. AN, BN, and BED mothers reported greater gestational weight gain, and smoking was elevated in all eating disorder groups. BED mothers had higher birth weight babies, lower risk of small for gestational age, and higher risk of large for gestational age and cesarean section than the referent. Pre-pregnancy BMI and gestational weight gain attenuated the effects.

CONCLUSION

BED influences birth outcomes either directly or via higher maternal weight and gestational weight gain. The absence of differences in AN and EDNOS-P may reflect small numbers and lesser severity in population samples. Adequate gestational weight gain in AN may mitigate against adverse birth outcomes. Detecting eating disorders in pregnancy could identify modifiable factors (e.g., high gestational weight gain, binge eating, and smoking) that influence birth outcomes.

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.

Nausea and vomiting of pregnancy in women with bulimia nervosa and eating disorders not otherwise specified

OBJECTIVE

To explore the prevalence of pregnancy-related nausea (PN) and vomiting (PV), and hyperemesis gravidarum (HG), in women with bulimia nervosa (BN) and EDNOS purging subtype (EDNOS-P).

METHOD

Pregnant women (38,038) enrolled in the Norwegian Mother and Child Cohort Study had questionnaire-based information on eating disorder diagnosis and PN, PV, and HG. We estimated the odds for PN, PV, and HG using logistic regression.

RESULTS

Women with BN, purging subtype, but not women with BN, nonpurging subtype, had statistically significant higher odds of PN and PV compared to women without eating disorders. The EDNOS-P group showed significantly higher odds of PV. The odds of HG did not differ significantly between those with and without an eating disorder, or across eating disorder subtypes.

CONCLUSION

Our results suggest that eating disorders marked by the symptom of purging are associated with increased odds of PN and PV.

Dimensional representations of DSM-IV cluster B personality disorders in a population-based sample of Norwegian twins: a multivariate study

BACKGROUND

The personality disorders (PDs) in the 'dramatic' cluster B [antisocial (ASPD), histrionic (HPD), narcissistic (NPD) and borderline (BPD)] demonstrate co-morbidity. However, the degree to which genetic and/or environmental factors influence their co-occurrence is not known and, with the exception of ASPD, the relative impact of genetic and environmental risk factors on liability to the cluster B PDs has not been conclusively established.

METHOD

PD traits were assessed in 1386 Norwegian twin pairs between the age of 19 and 35 years using the Structured Interview for DSM-IV Personality Disorders (SIDP-IV). Using the statistical package Mx, multivariate twin models were fitted to dimensional representations of the PDs.

RESULTS

The best-fitting model, which did not include sex or shared family environment effects, included common genetic and environmental factors influencing all four dramatic PD traits, and factors influencing only ASPD and BPD. Heritability was estimated at 38% for ASPD traits, 31% for HPD traits, 24% for NPD traits and 35% for BPD traits. BPD traits had the lowest and ASPD traits the highest disorder-specific genetic variance.

CONCLUSION

The frequently observed co-morbidity between cluster B PDs results from both common genetic and environmental influences. Etiologically, cluster B has a 'substructure' in which ASPD and BPD are more closely related to each other than to the other cluster B disorders.

Maternal eating disorders influence sex ratio at birth

We explored sex ratio at birth, defined as the proportion of male live births, in women with anorexia nervosa, bulimia nervosa, binge eating disorder, and eating disorders not otherwise specified-purging type (EDNOS-P) relative to a referent group in a large population-based sample of 38,340 pregnant women in Norway. Poisson regressions were adjusted for mother's age, pre-pregnancy BMI, lifetime smoking status, maternal education, income, marital status, gestational age, and parity. Lower proportions of male live births were observed in the anorexia and bulimia groups, while binge eating disorder and EDNOS-P were associated with a higher proportion of male births. These data suggest that maternal eating disorders may influence offspring sex and that the direction of effect may vary by eating disorder subtype. If confirmed, this finding could provide evidence in formulating hypotheses regarding the consequences of eating disorders and determinants of sex ratio at birth.

Genetics of personality disorders

This review of the literature on genetic contributions to the etiology of personality disorders broadly follows the DSM classification, and begins by evaluating the current evidence for genetic influences on the DSM axis II disorders. One of the most exciting directions in psychiatric genetics is the rapidly developing field of molecular genetic studies aiming to identify specific genes correlated with psychiatric phenotypes. Personality disorders, like most other psychiatric diagnostic categories, are etiologically complex, which implies that they are influenced by several genes and several environmental factors. The interplay between genes and the environment is a field that is receiving increasing attention and is addressed both in relation to quantitative and molecular methods.

Nutrient and food group intakes of women with and without bulimia nervosa and binge eating disorder during pregnancy

BACKGROUND

Little is known concerning the dietary habits during pregnancy of women with eating disorders that may lie in the causal pathway of adverse birth outcomes.

OBJECTIVE

We examined the nutrient and food group intakes of women with bulimia nervosa and binge-eating disorder during pregnancy and compared these with intakes of women with no eating disorders.

DESIGN

Data on 30,040 mother-child pairs from the prospective Norwegian Mother and Child Cohort Study were used in cross-sectional analyses. Dietary information was collected by using a food-frequency questionnaire during the first half of pregnancy. Statistical testing by eating disorder categories with the non-eating-disorder category as the referent group was conducted by using log means adjusted for confounding and multiple comparisons. Food group differences were analyzed by using a Wilcoxon's two-sided normal approximation test that was also adjusted for multiple comparisons.

RESULTS

Women with binge-eating disorder before and during pregnancy had higher intakes of total energy, total fat, monounsaturated fat, and saturated fat, and lower intakes of folate, potassium, and vitamin C than the referent (P < 0.02). Women with incident binge-eating disorder during pregnancy had higher intakes of total energy and saturated fat than the referent (P = 0.01). Several differences emerged in food group consumption between women with and without eating disorders, including intakes of artificial sweeteners, sweets, juice, fruit, and fats.

CONCLUSION

Women with bulimia nervosa before and during pregnancy and those with binge-eating disorder before pregnancy exhibit dietary patterns that differ from those in women without eating disorders, that are reflective of their symptomatology, and that may influence pregnancy outcomes.

Psychosocial factors associated with broadly defined bulimia nervosa during early pregnancy: findings from the Norwegian mother and child cohort study

OBJECTIVE

The purpose of the present study was to investigate the relationship between psychosocial characteristics and broadly defined bulimia nervosa during early pregnancy, including factors associated with continuation, incidence and remission.

METHOD

A total of 41 157 women completed questionnaires at approximately gestation week 18, including items on eating disorders and psychosocial characteristics as a part of Norwegian Mother and Child Cohort Study conducted by the Norwegian Institute of Public Health.

RESULTS

Incident bulimia nervosa during the first trimester was significantly associated with symptoms of anxiety and depression and low self-esteem and life satisfaction, whereas remission was significantly associated with higher self-esteem and life satisfaction. Continuation was not significantly related to any of the psychosocial variables tested.

CONCLUSION

Onset of bulimia nervosa during pregnancy is associated with mood and anxiety symptoms. Remission of bulimic symptoms and new onset of bulimia nervosa are associated with opposite profiles of self-esteem, and life satisfaction measures.

Familiality and heritability of binge eating disorder: results of a case-control family study and a twin study

OBJECTIVE

To estimate the familiality and heritability of binge eating disorder (BED).

METHOD

We used a new ACE structural equation model to estimate heritability from a case-control family study of BED conducted in the Boston area. The sample consisted of 150 overweight/obese probands with lifetime BED by DSM-IV criteria, 150 overweight/obese probands without lifetime BED, and 888 of their first-degree relatives. We compared our findings with those from a study of binge eating (in the absence of compensatory behaviors) among 7,831 Norwegian twins.

RESULTS

The prevalence of BED differed by sex and by age. In the case-control family study, BED was found to aggregate in families, and heritability was estimated as 57% (CI: 30-77%). Including shared environment did not substantially improve the model's fit, nor did allowing sex-specific heritability. Findings from the twin study were similar.

CONCLUSION

BED appears to aggregate in families and have a significant genetic component.

Passive-aggressive (negativistic) personality disorder: a population-based twin study

The objective of this study was to investigate the familial aggregation of passive aggressive personality disorder (PAPD), and explore issues regarding PAPD raised by the DSM-IV Personality Disorder Work Group. Two thousand seven hundred and ninety-four Norwegian twins from the population-based Norwegian Institute of Public Health Twin Panel were interviewed with the Structured Interview for DSM-IV Personality (SIDP-IV). Because of the rarity of the twins meeting full diagnostic criteria for PAPD a dimensional representation of the disorder was used for the analyses. Overlap with other axis II disorders was assessed by polychoric correlations, while familial aggregation was explored by structural equation twin models. Overlap was highest with paranoid (r = 0.52) and borderline personality disorder (r = 0.53), and lowest with schizoid (r = 0.26). Significant familial aggregation was found for PAPD. The twin correlations and parameter estimates in the full model indicated genetic and shared environmental effects for females, and only shared environmental effects for males, but the prevalence of endorsed PAPD criteria in this community sample was too low to permit us to conclude with confidence regarding the relative influence of genetic and shared environmental factors on the familial aggregation of PAPD.

The relationship between depressive personality disorder and major depressive disorder: a population-based twin study

OBJECTIVE

One of the most important controversies regarding depressive personality disorder is the overlap with mood disorders. The aim of this study was to estimate the genetic and environmental sources of covariance between depressive personality disorder and major depressive disorder and to what extent genetic, shared, and unique environmental factors are specific to each disorder.

METHOD

A total of 2,801 young adult twins from the Norwegian Institute of Public Health Twin Panel were assessed at personal interview for depressive personality disorder and major depressive disorder with the Structured Interview for DSM-IV Personality and the Composite International Diagnostic Interview. Bivariate Cholesky models were fitted to the data by using the Mx statistical program.

RESULTS

In the best-fitting model, the covariation between depressive personality disorder and major depressive disorder were accounted for by genetic and unique environmental factors only. A model that did not include genetic factors specific to major depressive disorder was rejected. The authors found no clear evidence for gender differences in sources of comorbidity of depressive personality disorder and major depressive disorder.

CONCLUSIONS

Although depressive personality disorder and major depressive disorder share a substantial proportion of genetic and environmental risk factors, the results from this study support the hypothesis that the two disorders are distinct entities with overlapping, but not identical, etiologies.

A genetic study of the acute anxious response to carbon dioxide stimulation in man

People with panic disorder-agoraphobia and their relatives often react anxiously to CO(2)-enriched gas mixtures. Available data are not suited to disentangle genetic from common environmental causes of familial aggregation of CO(2) reactivity, nor provide quantitative estimations of the sources of trait variation. Three-hundred-forty-six twin pairs belonging to the general population-based Norwegian NIPH Mental Health Study underwent self-assessments of anxiety and of DSM-IV panic symptoms after inhalation of a 35%CO(2)-65%O(2) mixture. Two thresholds were employed - at sample's 75th and 90th percentiles of responses - to define provoked panic attacks and to calculate polychoric correlations. Variance components were estimated by structural equation modelling (SEM). For definitions of responses based on the sum of all 13 panic symptoms, SEM could not discriminate between shared environmental versus genetic causes of familial resemblance for provoked attacks. For definitions of responses based on global anxiety, or on the sums of those symptoms (dyspnea, dizziness, palpitations) with highest variance post-CO(2), the best-fitting models indicated additive genetic factors as the sole causes for within-family resemblance. Best-fit heritability estimates ranged from 0.42 to 0.57. Genetic and idiosyncratic environmental factors explain most of individual differences in reactivity to hypercapnia. Within-family similarities for this trait are largely explained by genetic determinants.

Genetic epidemiology, endophenotypes, and eating disorder classification

OBJECTIVE

To explore how genetic epidemiology has informed the identification of endophenotypes and how endophenotypes may inform future classification of eating disorders.

METHOD

Literature review and synthesis.

RESULTS

Although a number of endo- and subphenotypes have been suggested for eating disorders, few reach the rigorous definitions developed for candidate endophenotypes.

CONCLUSION

Further study of endophenotypes and subphenotypes for eating disorders may assist with developing a more homogenous classification system that more closely reflects underlying biological mechanisms, and provides a clearer focus for the development of coherent models and treatments.

The relationship between avoidant personality disorder and social phobia: a population-based twin study

OBJECTIVE

The purpose of this study was to determine the sources of comorbidity for social phobia and dimensional representations of avoidant personality disorder by estimating to what extent the two disorders are influenced by common genetic and shared or unique environmental factors versus the extent to which these factors are specific to each disorder.

METHOD

Young adult female-female twin pairs (N=1,427) from the Norwegian Institute of Public Health Twin Panel were assessed at personal interview for avoidant personality disorder and social phobia using the Structured Interview for DSM-IV Personality and the Composite International Diagnostic Interview. Bivariate Cholesky models were fitted using the Mx statistical program.

RESULTS

The best-fitting model included additive genetic and unique environmental factors only. Avoidant personality disorder and social phobia were influenced by the same genetic factors, whereas the environmental factors influencing the two disorders were uncorrelated.

CONCLUSIONS

Within the limits of statistical power, these results suggest that there is a common genetic vulnerability to avoidant personality disorder and social phobia in women. An individual with high genetic liability will develop avoidant personality disorder versus social phobia entirely as a result of the environmental risk factors unique to each disorder. The results are in accordance with the hypothesis that psychobiological dimensions span the axis I and axis II disorders.

Patterns of remission, continuation and incidence of broadly defined eating disorders during early pregnancy in the Norwegian Mother and Child Cohort Study (MoBa)

BACKGROUND

We explored the course of broadly defined eating disorders during pregnancy in the Norwegian Mother and Child Cohort Study (MoBa) at the Norwegian Institute of Public Health.

METHOD

A total of 41,157 pregnant women, enrolled at approximately 18 weeks' gestation, had valid data from the Norwegian Medical Birth Registry. We collected questionnaire-based diagnostic information on broadly defined anorexia nervosa (AN), and bulimia nervosa (BN), and eating disorders not otherwise specified (EDNOS). EDNOS subtypes included binge eating disorder (BED) and recurrent self-induced purging in the absence of binge eating (EDNOS-P). We explored rates of remission, continuation and incidence of BN, BED and EDNOS-P during pregnancy.

RESULTS

Prepregnancy prevalence estimates were 0.1% for AN, 0.7% for BN, 3.5% for BED and 0.1% for EDNOS-P. During early pregnancy, estimates were 0.2% (BN), 4.8% (BED) and 0.1% (EDNOS-P). Proportions of individuals remitting during pregnancy were 78% (EDNOS-P), 40% (BN purging), 39% (BED), 34% (BN any type) and 29% (BN non-purging type). Additional individuals with BN achieved partial remission. Incident BN and EDNOS-P during pregnancy were rare. For BED, the incidence rate was 1.1 per 1000 person-weeks, equating to 711 new cases of BED during pregnancy. Incident BED was associated with indices of lower socio-economic status.

CONCLUSIONS

Pregnancy appears to be a catalyst for remission of some eating disorders but also a vulnerability window for the new onset of broadly defined BED, especially in economically disadvantaged individuals. Vigilance by health-care professionals for continuation and emergence of eating disorders in pregnancy is warranted.

The heritability of cluster A personality disorders assessed by both personal interview and questionnaire

BACKGROUND

Personality disorders (PDs) as assessed by questionnaires and personal interviews are heritable. However, we know neither how much unreliability of measurement impacts on heritability estimates nor whether the genetic and environmental risk factors assessed by these two methods are the same. We wish to know whether the same set of PD vulnerability factors are assessed by these two methods.

METHOD

A total of 3334 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel (NIPHTP) completed a questionnaire containing 91 PD items. One to 6 years later, 1386 of these pairs were interviewed with the Structured Interview for DSM-IV Personality (SIDP-IV). Self-report items predicting interview results were selected by regression. Measurement models were fitted using Mx.

RESULTS

In the best-fit models, the latent liabilities to paranoid personality disorder (PPD), schizoid personality disorder (SPD) and schizotypal personality disorder (STPD) were all highly heritable with no evidence of shared environmental effects. For PPD and STPD, only unique environmental effects were specific to the interview measure whereas both environmental and genetic effects were found to be specific to the questionnaire assessment. For SPD, the best-fit model contained genetic and environmental effects specific to both forms of assessment.

CONCLUSIONS

The latent liabilities to the cluster A PDs are highly heritable but are assessed by current methods with only moderate reliability. The personal interviews assessed the genetic risk for the latent trait with excellent specificity for PPD and STPD and good specificity for SPD. However, for all three PDs, the questionnaires were less specific, also indexing an independent set of genetic risk factors.

Genetic and environmental influences on dimensional representations of DSM-IV cluster C personality disorders: a population-based multivariate twin study

BACKGROUND

The DSM-IV cluster C Axis II disorders include avoidant (AVPD), dependent (DEPD) and obsessive-compulsive (OCPD) personality disorders. We aimed to estimate the genetic and environmental influences on dimensional representations of these disorders and examine the validity of the cluster C construct by determining to what extent common familial factors influence the individual PDs.

METHOD

PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV) in a sample of 1386 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel (NIPHTP). A single-factor independent pathway multivariate model was applied to the number of endorsed criteria for the three cluster C disorders, using the statistical modeling program Mx.

RESULTS

The best-fitting model included genetic and unique environmental factors only, and equated parameters for males and females. Heritability ranged from 27% to 35%. The proportion of genetic variance explained by a common factor was 83, 48 and 15% respectively for AVPD, DEPD and OCPD. Common genetic and environmental factors accounted for 54% and 64% respectively of the variance in AVPD and DEPD but only 11% of the variance in OCPD.

CONCLUSION

Cluster C PDs are moderately heritable. No evidence was found for shared environmental or sex effects. Common genetic and individual environmental factors account for a substantial proportion of the variance in AVPD and DEPD. However, OCPD appears to be largely etiologically distinct from the other two PDs. The results do not support the validity of the DSM-IV cluster C construct in its present form.