Kerry L. Jang

The role of genes and environment on trauma exposure and posttraumatic stress disorder symptoms: A review of twin studies☆

Behavioral-genetic (twin) methods are important tools for understanding the etiology of trauma exposure and posttraumatic stress disorder (PTSD). The purpose of the present article is to synthesize the results obtained from twin studies and outline important avenues for further investigation. Twin research to date suggests that: (1) exposure to assaultive trauma is moderately heritable whereas exposure to non-assaultive trauma is not, (2) PTSD symptoms are moderately heritable, and (3) comorbidity of PTSD with other disorders may be partly due to shared genetic and environmental influences. Remarkably little is known about whether the observed comorbidity of PTSD with particular personality traits and poor physical health is due to shared genetic or environmental factors. Similarly, little is known about whether gene-environment interactions play an important role in trauma exposure and PTSD. Further research is required to clarify these issues and to determine whether findings to date, obtained mostly from male combat veterans, generalize to other populations. Research programs that integrate behavioral-genetics with molecular genetics and with cognitive-behavioral conceptualizations and research methods may deepen our understanding of the complex links among genes, brain, cognition, emotion, and the environment.

Twin study of dissociative experience.

The relative influence of genetic and environmental influences on measures of pathological and nonpathological dissociative experience was estimated using a classic twin-study design. Subjects were 177 monozygotic and 152 dizygotic volunteer general population twin pairs who completed two measures of dissociative capacity identified from the items comprising the Dissociative Experiences Scale (DES). Additive genetic influences accounted for 48% and 55% of the variance in scales measuring pathological and nonpathological dissociative experience, respectively. Heritability estimates did not differ by gender. The genetic correlation between these measures was estimated at .91, suggesting common genetic factors underlying pathological and nonpathological dissociative capacity. Genetic and environmental correlations between the DES scales and measures of personality disorder traits (Dimensional Assessment of Personality Pathology-Basic Questionnaire; DAPP-BQ) were also estimated. Significant genetic correlations (median = .38) were found between the DES scales and DAPP-BQ cognitive dysregulation, affective lability, and suspiciousness, suggesting that the genetic factors underlying particular aspects of personality disorder also influence dissociative capacity.

Heritability of social anxiety-related concerns and personality characteristics: a twin study.

Negative evaluation fears figure prominently in the cognitive psychology of patients with social phobia. In this study, we examine the heritability of negative evaluation fears by using a twin sample. The authors also examine the relationships between negative evaluation fears and personality dimensions relevant to social phobia. Scores on the brief version of the Fear of Negative Evaluation Scale (BFNE) were examined in a sample of 437 (245 monozygotic and 192 dizygotic) twin pairs. Biometrical model fitting was conducted by using standard statistical methods. Genetic and environmental correlations with personality dimensions (from the Dimensional Assessment of Personality Pathology-Basic Questionnaire) were also calculated. Broad heritability estimate of the BFNE was 48%. Additive genetic effects and unique environmental effects emerged as the primary influences on negative evaluation fears. Genetic correlations between BFNE scores and the submissiveness, anxiousness, and social avoidance facets of the Dimensional Assessment of Personality Pathology-Basic Questionnaire were high (rg = .78 to .80). A cognitive dimension central to the phenomenology (and, perhaps, cause) of social phobia, the fear of being negatively evaluated, is moderately heritable. Moreover, the same genes that influence negative evaluation fears appear to influence a cluster of anxiety-related personality characteristics. Implications and limitations of these findings are discussed.

Substance and artifact in the higher-order factors of the Big Five.

J. M. Digman (1997) proposed that the Big Five personality traits showed a higher-order structure with 2 factors he labeled alpha and beta. These factors have been alternatively interpreted as heritable components of personality or as artifacts of evaluative bias. Using structural equation modeling, the authors reanalyzed data from a cross-national twin study and from American cross-observer studies and analyzed new multimethod data from a German twin study. In all analyses, artifact models outperformed substance models by root-mean-square error of approximation criteria, but models combining both artifact and substance were slightly better. These findings suggest that the search for the biological basis of personality traits may be more profitably focused on the 5 factors themselves and their specific facets, especially in monomethod studies.

Differentiating normal, abnormal, and disordered personality

Interest in the interface between normality and psychopathology was renewed with the publication of DSM‐III more than 20 years ago. The use of a separate axis to classify disorders of personality brought increased attention to these conditions. At the same time, the definition of personality disorder as inflexible and maladaptive traits stimulated interest in the relationship between normal and disordered personality structure and functioning. The evidence suggests that the traits delineating personality disorder are continuous with normal variation and that the structural relationships among these traits resemble the structures described by normative trait theories. Recognition that personality disorder represents the extremes of trait dimensions emphasizes the importance of differentiating normal, abnormal, and disordered personality. It is argued that while abnormal personality may be considered extreme variation, personality disorder is more than statistical variation. A definition of personality disorder is suggested based on accounts of the adaptive functions of personality. Copyright

Etiology of obsessions and compulsions: A behavioral-genetic analysis.

It is unknown whether various types of obsessive-compulsive (OC) symptoms have a common genetic or environmental etiology. For example, it is unknown whether hoarding is etiologically associated with prototypic OC symptoms, such as washing, checking, and obsessing. Also unknown is whether particular OC-related symptoms are etiologically linked to the general tendency to experience emotional distress (negative emotionality). To investigate these and other issues, a community sample of 307 pairs of monozygotic and dizygotic adult twins provided scores on 6 OC-related symptoms (obsessing, neutralizing, checking, washing, ordering, and hoarding) and 2 markers of negative emotionality (trait anxiety and affective lability). Genetic factors accounted for 40%-56% of variance in the 8 phenotypic scores (M = 49% of variance for OC-related symptoms). Remaining variance was due to nonshared (person-specific) environment. More detailed analyses revealed a complex etiologic architecture, where OC-related symptoms arise from a mix of common and symptom-specific genetic and environmental factors. A general genetic factor was identified, which influenced all symptoms and negative emotionality. An environmental factor was identified that influenced all symptoms but did not influence negative emotionality. Each of the 6 types of symptoms was also shaped by its own set of symptom-specific genetic and environmental factors. The importance of genetic factors did not vary as a function of age or sex, and the architecture of general and specific etiologic factors was replicated for participants having relatively more severe OC symptoms. Gene-environment interactions were identified. Implications for an etiology-based classification system are discussed.

The genetic and environmental basis of the relationship between schizotypy and personality: a twin study.

The clinical phenotype commonly referred to as schizotypy is used in two different ways in psychiatric practice. One usage emphasizes psychosis-proneness where schizotypy is considered part of the schizophrenia spectrum. The other emphasizes personality aberrations and is classed as a personality disorder. The present study provides evidence that schizotypy is a unitary construct and that features like schizophrenia and personality share a common genetic basis. A sample of 102 monozygotic and 90 dizygotic general population twin pairs completed measures of psychosis-proneness and traits delineating personality disorder. Multivariate genetic analyses showed that the observed relationship between psychotic and personality features is caused almost entirely by common genetic factors. Environmental factors appear to be unique to each measure. On the basis of these findings, it is suggested that the environment mediates change in personality function to psychosis as proposed by Meehls original concept of schizotaxia.

Biopsychosocial etiology of obsessions and compulsions: an integrated behavioral-genetic and cognitive-behavioral analysis.

Accumulating evidence suggests that particular kinds of dysfunctional beliefs contribute to obsessive-compulsive (OC) symptoms. Three domains of beliefs have been identified: (a) perfectionism and intolerance of uncertainty, (b) overimportance of thoughts and the need to control thoughts, and (c) inflated responsibility and overestimation of threat. These beliefs and OC symptoms are both heritable. Although it is widely acknowledged that OC symptoms probably have a complex biopsychosocial etiology, to our knowledge there has been no previous attempt to integrate dysfunctional beliefs and genetic factors into a unified, empirically supported model. The present study was an initial step in that direction. A community sample of monozygotic and dizygotic twins (N = 307 pairs) completed measures of dysfunctional beliefs and OC symptoms. Structural equation modeling was used to compare 3 models: (a) the belief causation model, in which genetic and environmental factors influence beliefs and OC symptoms, and beliefs also influence symptoms; (b) the symptom causation model, which is the same as (a) except that symptoms cause beliefs; and (c) the belief coeffect model, in which beliefs and OC symptoms are the product of common genetic and environmental factors, and beliefs have no causal influence on symptoms. The belief causation model was the best fitting model. Beliefs accounted for a mean of 18% of phenotypic variance in OC symptoms. Genetic and environmental factors, respectively, accounted for an additional 36% and 47% of phenotypic variance. The results suggest that further biopsychosocial investigations may be fruitful for unraveling the etiology of obsessions and compulsions.

A behavior genetic study of the connection between social values and personality.

The present research examined the extent to which relations between social values and personality are due to shared genetic or environmental factors. Using the Rokeach (1973) Value Survey and a scoring key from Schwartz and Bilsky (1990), seven value scores (enjoyment, achievement, self-direction, maturity, prosocial, security, and restrictive conformity) were derived in a sample of twins. As expected, all of the value scales were found to have a significant genetic component, with values ranging from 36% for enjoyment to 63% for prosocial, and there were numerous significant phenotypic correlations found between the value scales and personality scores. Most important, bivariate genetic analyses revealed that some of these phenotypic correlations could be attributed to common genetic or environmental factors.

The relationship between the Zuckerman–Kuhlman Personality Questionnaire and traits delineating personality pathology

Abstract This study explores the relationship between the Zuckerman–Kuhlman Personality Questionnaire (ZKPQ) scales of normative personality with basic dimensions of disordered personality assessed by the Dimensional Assessment of Personality Pathology—Basic Questionnaire (DAPP-BQ). The DAPP-BQ was used to establish the relationship between ZKPQ scales and dimensions of personality disorder because the relationship of the DAPP-BQ scales to the other major models of personality has been established. One hundred and forty-nine university students in China completed the Chinese language versions of the DAPP-BQ and ZKPQ. The psychometric properties of the scales in this sample were satisfactory. The factorial analysis of the ZKPQ and DAPP-BQ scales yielded five factors that were named Emotional Dysregulation, Dissocial, Impulsive Misconduct, Inhibition, and Compulsivity.