General Genes

Dimensional and transdiagnostic phenotypes in psychiatric genome-wide association studies

Genome-wide association studies (GWAS) provide biological insights into disease onset and progression and have potential to produce clinically useful biomarkers. A growing body of GWAS focuses on quantitative and transdiagnostic phenotypic targets, such as symptom severity or biological markers, to enhance gene discovery and the translational utility of genetic findings. The current review discusses such phenotypic approaches in GWAS across major psychiatric disorders. We identify themes and recommendations that emerge from the literature to date, including issues of sample size, reliability, convergent validity, sources of phenotypic information, phenotypes based on biological and behavioral markers such as neuroimaging and chronotype, and longitudinal phenotypes. We also discuss insights from multi-trait methods such as genomic structural equation modelling. These provide insight into how hierarchical 'splitting' and 'lumping' approaches can be applied to both diagnostic and dimensional phenotypes to model clinical heterogeneity and comorbidity. Overall, dimensional and transdiagnostic phenotypes have enhanced gene discovery in many psychiatric conditions and promises to yield fruitful GWAS targets in the years to come.

A multivariate twin study of the genetic association between present moment attention and subjective wellbeing

Considerable evidence supports the role of present-moment attention, a central feature of mindfulness, in subjective wellbeing maintenance and enhancement. Yet it is not clear why such a relation exists. This study examined the genetic and environmental contributions of present-moment attention to subjective wellbeing. Consistent with the "generalist genes hypothesis" and prior evidence, we hypothesized that presence and subjective wellbeing would show a substantial genetic correlation and smaller environmental correlation. Using a large epidemiological sample of healthy 16-year-old twins in the United Kingdom (N = 1136 monozygotic (MZ) and dizygotic (DZ) twin pairs), genetic overlap was found between presence and the cognitive component of subjective wellbeing (life satisfaction), and to a lesser extent, the affective component of subjective wellbeing (operationalized as happiness). The non-shared environmental overlap between these constructs was substantial. This study provides the first evidence known to us showing that present-centered attention, a primary component of mindfulness, has both genetic and environmental overlap with subjective wellbeing. The findings have implications for understanding mechanisms by which presence is associated with positive emotions and life satisfaction, and suggest, pending additional research, that mindfulness-based interventions to enhance wellbeing may be best suited to those with a genetic propensity toward mindful presence.

Shared genetic influences between depression and conduct disorder in children and adolescents: A systematic review

INTRODUCTION

The co-occurrence between major depression disorder (MDD) and conduct disorder (CD) is common across development and represents a significant risk factor for future psychiatric problems and long-term impairment. Large-scale quantitative genetic studies suggest that the MDD-CD co-occurrence may be partly explained by shared genetic vulnerability factors, in line with transdiagnostic models of psychopathology, but no systematic synthesis of the literature is currently available.

METHODS

We therefore conducted a systematic review of the available genetic literature on the co-occurrence between MDD and CD in children and adolescents. We identified 10 eligible studies, including 5 cross-sectional bivariate/multivariate twin studies, 3 longitudinal bivariate/multivariate twin studies, and 2 latent profile/trajectory twin studies.

RESULTS

Most of the reviewed studies found a strong contribution of shared genetic factors on the covariation between depression and conduct problems, in line with the prominent effect of a common genetic liability across development.

LIMITATIONS

The scientific literature on this psychiatric comorbidity is still limited, as it solely consists of twin studies from high income countries.

CONCLUSION

Considering the joint burden of MDD and CD on youth, families and society worldwide, future studies are needed to better investigate the shared risk processes of these frequently co-occurring conditions, in order to inform new treatments through personalized medicine.

Generalist genes and specialist environments for adolescent internalizing and externalizing problems: A test of severity and directionality

The generalist genes specialist environment model, when applied to developmental psychopathology, predicts that genetic influences should explain variance that is shared across internalizing and externalizing problems, whereas environmental influences should explain variance that distinguishes the two overarching problem types. The present study is a direct test of this hypothesis, leveraging a sample of 708 twins and siblings (aged 10-18 years, 93% White) from the United States. Measures of severity of symptoms, regardless of type, and of directionality of symptoms - whether the adolescent tended to exhibit more externalizing or internalizing problems - were subjected to genetic (A), shared environmental (C), and nonshared environmental (E) (ACE) variance decompositions. As expected, severity of problems was under substantial genetic influence, but there were also significant shared and nonshared environmental influences. Contrary to the generalist genes specialist environment model, directionality of problem type was also under considerable genetic influence, with modest nonshared environmental influence. Findings corroborate existing evidence from other designs highlighting the role of familial influences (including generalist genes) in comorbidity of adolescent internalizing and externalizing problems, but suggest that the specialist environments hypothesis may not be the key factor in distinguishing problem type.

Why do depression, conduct, and hyperactivity symptoms co-occur across adolescence? The role of stable and dynamic genetic and environmental influences

Depression, conduct, and hyperactivity symptoms are chronic and frequently co-occur in adolescence. Common genetic and environmental vulnerability to these conditions have previously been demonstrated, however, the manner in which common versus disorder-specific etiological influences operate across development and maintain symptom co-occurrence is unclear. Thus, the current study investigated the role of common genetic and environmental influences in the comorbidity of depression, conduct, and hyperactivity across adolescence. Over 10,000 twins and their parents reported adolescents' symptoms at mean ages 11 and 16 years. Biometric independent pathway models were fitted to estimate genetic and environmental contributions to the continuity of symptom co-occurrence over time, as well as time- and symptom-specific influences. Results found that a common stable genetic factor accounted for the concurrent and longitudinal co-occurrence of depression, conduct, and hyperactivity symptoms. New genetic influences common to these three symptom scales emerged at 16 years, and further contributed to symptom co-occurrence. Conversely, environmental influences largely contributed to the time-specific associations. The findings were generally consistent for self- and parent-reported symptoms. Overall, the results suggest that stable, overlapping genetic influences contribute to the co-occurrence of depression, conduct, and hyperactivity symptoms across adolescence. The results are in line with hierarchical causal models of psychopathology, which posit that much of the developmental co-occurrence between different symptoms is due to common liability. Specifically, current findings indicate that only genetic influences constitute common liability over time. Future studies should identify genetically influenced transdiagnostic risk and maintenance factors to inform prevention and treatment of comorbid internalizing and externalizing symptoms in adolescence.

Trajectories of internalizing and externalizing problems in preschoolers of depressed mothers: Examining gender differences

BACKGROUND

This study sought to examine the development of global and co-occurring internalizing and externalizing problems in preschoolers whose mothers have high depressive symptoms, a topic that is less often studied.

METHOD

This longitudinal study consisted of 201 families with mothers who reported clinically-relevant depressive symptoms. Mothers rated their depressive symptoms across children's first two years. Children's internalizing and externalizing problems were reported by caregivers or teachers at three waves in early childhood.

RESULTS

Using growth curve analyses, findings revealed gender-variant patterns in the development of internalizing and externalizing problems. Across early childhood, boys of mothers with depressive symptoms exhibited stable internalizing and increasing externalizing problems whereas girls exhibited declining trajectories of both problems. Further examination of within-gender variation indicated the heterogeneity in trajectories of internalizing and externalizing problems only among girls. Moreover, the co-occurrence of internalizing and externalizing problems was evident in both genders.

LIMITATIONS

This study was based on a community sample and thus caution should be exerted to generalize findings to clinical samples.

CONCLUSIONS

Findings suggest that boys may be at heightened risk for behavioral problems in the face of high maternal depressive symptoms and that internalizing and externalizing problems tend to co-occur in this group of at-risk preschoolers.

Mindfulness and associations with symptoms of insomnia, anxiety and depression in early adulthood: A twin and sibling study

This study investigated associations between mindfulness and symptoms of insomnia, depression and anxiety. Mindfulness was disaggregated into five subscales: 'nonreactivity to inner experience', 'observing', 'acting with awareness', 'describing' and 'nonjudging of inner experience'. Twin models were used to examine genetic and environmental influences on mindfulness, symptoms of insomnia, depression and anxiety and on their associations. Data came from a longitudinal twin/sibling study (G1219) comprising 862 individuals (age range 22-32 years, 66% females). Less mindfulness was associated with greater symptoms of insomnia, depression and anxiety (r = .22-.48). Of the mindfulness subscales, 'nonjudging of inner experience' was most strongly associated with the other traits. Overall mindfulness was largely influenced by non-shared environmental factors (E = .72) although familial influences played a role for overall mindfulness, as well as for the 'acting with awareness' and 'describing' subscales. The genetic correlations between overall mindfulness and symptoms of insomnia, depression and anxiety ranged from .32 to .75 (but were non-significant), while the shared environmental correlations ranged from -.78 to .79 (also non-significant). The non-shared environmental influences between these three variables were moderately, significantly correlated (rE = .21-.55).

Genetic and environmental aetiologies of associations between dispositional mindfulness and ADHD traits: a population-based twin study

To get additional insight into the phenotype of attentional problems, we examined to what extent genetic and environmental factors explain covariation between lack of dispositional mindfulness and attention-deficit/hyperactivity disorder (ADHD) traits in youth, and explored the incremental validity of these constructs in predicting life satisfaction. We used data from a UK population-representative sample of adolescent twins (N = 1092 pairs) on lack of dispositional mindfulness [Mindful Attention Awareness Scale (MAAS)], ADHD traits [Conners' Parent Rating Scale-Revised (CPRS-R): inattentive (INATT) and hyperactivity/impulsivity (HYP/IMP) symptom dimensions] and life satisfaction (Students' Life Satisfaction Scale). Twin model fitting analyses were conducted. Phenotypic correlations (r_p) between MAAS and CPRS-R (INATT: r_p = 0.18, HYP/IMP: r_p = 0.13) were small, but significant and largely explained by shared genes for INATT (% r_p INATT-MAAS due to genes: 93%, genetic correlation r_A = 0.37) and HYP/IMP (% r_p HYP/IMP-MAAS due to genes: 81%; genetic correlation r_A = 0.21) with no significant contribution of environmental factors. MAAS, INATT and HYP/IMP significantly and independently predicted life satisfaction. Lack of dispositional mindfulness, assessed as self-reported perceived lapses of attention (MAAS), taps into an aspect of attentional functioning that is phenotypically and genetically distinct from parent-rated ADHD traits. The clinically relevant incremental validity of both scales implicates that MAAS could be used to explore the underlying mechanisms of an aspect of attentional functioning that uniquely affects life satisfaction and is not captured by DSM-based ADHD scales. Further future research could identify if lack of dispositional mindfulness and high ADHD traits can be targeted by different therapeutic approaches resulting in different effects on life satisfaction.

Atypical fetal development: Fetal alcohol syndrome, nutritional deprivation, teratogens, and risk for neurodevelopmental disorders and psychopathology

Accumulating evidence indicates that the fetal environment plays an important role in brain development and sets the brain on a trajectory across the life span. An abnormal fetal environment results when factors that should be present during a critical period of development are absent or when factors that should not be in the developing brain are present. While these factors may acutely disrupt brain function, the real cost to society resides in the long-term effects, which include important mental health issues. We review the effects of three factors, fetal alcohol exposure, teratogen exposure, and nutrient deficiencies, on the developing brain and the consequent risk for developmental psychopathology. Each is reviewed with respect to the evidence found in epidemiological and clinical studies in humans as well as preclinical molecular and cellular studies that explicate mechanisms of action.

Genetics of co-developing conduct and emotional problems during childhood and adolescence

Common genetic influences offer a partial explanation for comorbidity between different psychiatric disorders1-3. However, the genetics underlying co-development-the cross-domain co-occurrence of patterns of change over time-of psychiatric symptoms during childhood and adolescence has not been well explored. Here, we show genetic influence on joint symptom trajectories of parent-reported conduct and emotional problems (overall N = 15,082) across development (4-16 years) using both twin- and genome-wide polygenic score analyses (genotyped N = 2,610). Specifically, we found seven joint symptom trajectories, including two characterized by jointly stable and jointly increasing symptoms of conduct and emotional problems, respectively (7.3% of the sample, collectively). Twin modelling analyses revealed substantial genetic influence on trajectories (heritability estimates range of 0.41-0.78). Furthermore, individuals' risk of being classified in the most symptomatic trajectory classes was significantly predicted by polygenic scores for years-of-education-associated alleles and depressive symptoms-associated alleles. Complementary analyses of child self-reported symptoms across late childhood and early adolescence yielded broadly similar results. Taken together, our results indicate that genetic factors are involved in the co-development of conduct and emotional problems across childhood and adolescence, and that individuals with co-developing symptoms across multiple domains may represent a clinical subgroup characterized by increased levels of genetic risk.

Associations between the parent-child relationship and adolescent self-worth: a genetically informed study of twin parents and their adolescent children

BACKGROUND

Low self-worth during adolescence predicts a range of emotional and behavioural problems. As such, identifying potential sources of influence on self-worth is important. Aspects of the parent-child relationship are often associated with adolescent self-worth but to date it is unclear whether such associations may be attributable to familial confounding (e.g. genetic relatedness). We set out to clarify the nature of relationships between parental expressed affection and adolescent self-worth, and parent-child closeness and adolescent self-worth.

METHODS

We used data from the Twin and Offspring Study in Sweden, a children-of-twins sample comprising 909 adult twin pairs with adolescent children. Using these data we were able to apply structural equation models with which we could examine whether associations remained after accounting for genetic transmission.

RESULTS

Results demonstrated that parent-child closeness and parental-expressed affection were both phenotypically associated with adolescent self-worth. Associations could not be attributed to genetic relatedness between parent and child.

CONCLUSIONS

Parent-child closeness and parental affection are associated with adolescent self-worth above and beyond effects attributable to genetic relatedness. Data were cross-sectional, so the direction of effects cannot be confirmed but findings support the notion that positive parent-child relationships increase adolescent self-worth.

A Longitudinal Twin and Sibling Study of Associations between Insomnia and Depression Symptoms in Young Adults

STUDY OBJECTIVES

To estimate genetic and environmental influences on the associations between insomnia and depression symptoms concurrently and longitudinally.

METHODS

Behavioral genetic analyses were conducted on data from the British longitudinal G1219 twin/sibling study. One thousand five hundred fiftysix twins and siblings participated at Time 1 (mean age = 20.3 years, SD = 1.76). Eight hundred sixty-two participated at Time 2 (mean age = 25.2 years, SD = 1.73 years). Participants completed the Insomnia Symptoms Questionnaire and the Short Mood and Feelings Questionnaire to assess symptoms of insomnia and depression respectively.

RESULTS

Genetic effects accounted for 33% to 41% of the variance of the phenotypes. The phenotypic correlations were moderate (r = 0.34 to r = 0.52). The genetic correlations between the variables were high (0.73-1.00). Genetic effects accounted for a substantial proportion of the associations between variables (50% to 90%). Non-shared environmental effects explained the rest of the variance and covariance of the traits.

CONCLUSIONS

While genetic effects play a modest role in insomnia and depression symptoms separately, they appear to play a more central role in concurrent and longitudinal associations between these phenotypes. This should be acknowledged in theories explaining these common associations.

A longitudinal twin and sibling study of the hopelessness theory of depression in adolescence and young adulthood

BACKGROUND

Maladaptive cognitive biases such as negative attributional style and hopelessness have been implicated in the development and maintenance of depression. According to the hopelessness theory of depression, hopelessness mediates the association between attributional style and depression. The aetiological processes underpinning this influential theory remain unknown. The current study investigated genetic and environmental influences on hopelessness and its concurrent and longitudinal associations with attributional style and depression across adolescence and emerging adulthood. Furthermore, given high co-morbidity between depression and anxiety, the study investigated whether these maladaptive cognitions constitute transdiagnostic cognitive content common to both internalizing symptoms.

METHOD

A total of 2619 twins/siblings reported attributional style (mean age 15 and 17 years), hopelessness (mean age 17 years), and depression and anxiety symptoms (mean age 17 and 20 years).

RESULTS

Partial correlations revealed that attributional style and hopelessness were uniquely associated with depression but not anxiety symptoms. Hopelessness partially mediated the relationship between attributional style and depression. Hopelessness was moderately heritable (A = 0.37, 95% confidence interval 0.28-0.47), with remaining variance accounted for by non-shared environmental influences. Independent pathway models indicated that a set of common genetic influences largely accounted for the association between attributional style, hopelessness and depression symptoms, both concurrently and across development.

CONCLUSIONS

The results provide novel evidence that associations between attributional style, hopelessness and depression symptoms are largely due to shared genetic liability, suggesting developmentally stable biological pathways underpinning the hopelessness theory of depression. Both attributional style and hopelessness constituted unique cognitive content in depression. The results inform molecular genetics research and cognitive treatment approaches.

Longitudinal Stability of Genetic and Environmental Influences on the Association between Diurnal Preference and Sleep Quality in Young Adult Twins and Siblings

Overlapping genetic influences have been implicated in diurnal preference and subjective sleep quality. Our overall aim was to examine overlapping concurrent and longitudinal genetic and environmental effects on diurnal preference and sleep quality over ~5 years. Behavioral genetic analyses were performed on data from the longitudinal British G1219 study of young adult twins and nontwin siblings. A total of 1556 twins and siblings provided data on diurnal preference (Morningness-Eveningness Questionnaire) and sleep quality (Pittsburgh Sleep Quality Index) at time 1 (mean age = 20.30 years, SD = 1.76; 62% female), and 862 participated at time 2 (mean age = 25.30 years, SD = 1.81; 66% female). Preference for eveningness was associated with poorer sleep quality at both time points ( r = 0.25 [95% confidence intervals {CIs} = 0.20-0.30] and r = 0.21 [CI = 0.15-0.28]). There was substantial overlap in the genetic influences on diurnal preference and sleep quality individually, across time (genetic correlations [rAs]: 0.64 [95% CI = 0.59-0.67] and 0.48 [95% CI = 0.42-.053]). There were moderate genetic correlations between diurnal preference and sleep quality concurrently and longitudinally (rAs = 0.29-0.60). Nonshared environmental overlap was substantially smaller for all cross-phenotype associations (nonshared environmental correlations (rEs) = -0.02 to 0.08). All concurrent and longitudinal associations within and between phenotypes were largely accounted for by genetic factors (explaining between 60% and 100% of the associations). All shared environmental effects were nonsignificant. Nonshared environmental influences played a smaller role on the associations between phenotypes (explaining between -0.06% and 40% of the associations). These results suggest that to some extent, similar genes contribute to the stability of diurnal preference and sleep quality throughout young adulthood but also that different genes play a part over this relatively short time frame. While there was evidence of genetic overlap between phenotypes concurrently and longitudinally, the possible emergence of new genetic factors (or decline of previously associated factors) suggests that molecular genetic studies focusing on young adults should consider more tightly specified age groups, given that genetic effects may be time specific.

Annual Research Review: Sleep problems in childhood psychiatric disorders--a review of the latest science

BACKGROUND

Hippocrates flagged the value of sleep for good health. Nonetheless, historically, researchers with an interest in developmental psychopathology have largely ignored a possible role for atypical sleep. Recently, however, there has been a surge of interest in this area, perhaps reflecting increased evidence that disturbed or insufficient sleep can result in poor functioning in numerous domains. This review outlines what is known about sleep in the psychiatric diagnoses most relevant to children and for which associations with sleep are beginning to be understood. While based on a comprehensive survey of the literature, the focus of the current review is on the latest science (largely from 2010). There is a description of both concurrent and longitudinal links as well as possible mechanisms underlying associations. Preliminary treatment research is also considered which suggests that treating sleep difficulties may result in improvements in behavioural areas beyond sleep quality.

FINDINGS

To maximise progress in this field, there now needs to be: (a) greater attention to the assessment of sleep in children; (b) sleep research on a wider range of psychiatric disorders; (c) a greater focus on and examination of mechanisms underlying associations; (d) a clearer consideration of developmental questions and (e) large-scale well-designed treatment studies.

CONCLUSIONS

While sleep problems may sometimes be missed by parents and healthcare providers; hence constituting a hidden risk for other psychopathologies - knowing about these difficulties creates unique opportunities. The current excitement in this field from experts in diverse areas including developmental psychology, clinical psychology, genetics and neuropsychology should make these opportunities a reality.

The stability and change of etiological influences on depression, anxiety symptoms and their co-occurrence across adolescence and young adulthood

BACKGROUND

Depression and anxiety persist within and across diagnostic boundaries. The manner in which common v. disorder-specific genetic and environmental influences operate across development to maintain internalizing disorders and their co-morbidity is unclear. This paper investigates the stability and change of etiological influences on depression, panic, generalized, separation and social anxiety symptoms, and their co-occurrence, across adolescence and young adulthood.

METHOD

A total of 2619 twins/siblings prospectively reported symptoms of depression and anxiety at mean ages 15, 17 and 20 years.

RESULTS

Each symptom scale showed a similar pattern of moderate continuity across development, largely underpinned by genetic stability. New genetic influences contributing to change in the developmental course of the symptoms emerged at each time point. All symptom scales correlated moderately with one another over time. Genetic influences, both stable and time-specific, overlapped considerably between the scales. Non-shared environmental influences were largely time- and symptom-specific, but some contributed moderately to the stability of depression and anxiety symptom scales. These stable, longitudinal environmental influences were highly correlated between the symptoms.

CONCLUSIONS

The results highlight both stable and dynamic etiology of depression and anxiety symptom scales. They provide preliminary evidence that stable as well as newly emerging genes contribute to the co-morbidity between depression and anxiety across adolescence and young adulthood. Conversely, environmental influences are largely time-specific and contribute to change in symptoms over time. The results inform molecular genetics research and transdiagnostic treatment and prevention approaches.

Aetiological overlap between anxiety and attention deficit hyperactivity symptom dimensions in adolescence

BACKGROUND

Anxiety and attention-deficit/hyperactivity (ADH) problems are common in adolescence, often co-occur, and are characterised by high heterogeneity in their phenotypic expressions. Although it is known that anxiety and ADH problems correlate, the relationships between subtypes of anxiety and ADH problems have been scarcely investigated.

METHODS

Using a large population sample of adolescent twins and siblings we explored the phenotypic and aetiological association between anxiety subtypes (panic/agoraphobia, separation anxiety, social anxiety, physical injury fears, obsessive-compulsive symptoms and generalised anxiety) and the two ADH dimensions (attention problems and hyperactivity/impulsivity). Both phenotypes were assessed using self-report questionnaires.

RESULTS

The association between ADH problems and anxiety could be entirely attributed to attention problems, not hyperactivity/impulsivity. Most of the correlations between anxiety subtypes and attention problems showed an approximately equal role of genetic and nonshared environmental factors.

CONCLUSIONS

The high heterogeneity within anxiety and ADH problems should be taken into account in order to better understand comorbidity between them.

A multivariate twin study of trait mindfulness, depressive symptoms, and anxiety sensitivity

BACKGROUND

Mindfulness-based therapies have been shown to be effective in treating depression and reducing cognitive biases. Anxiety sensitivity is one cognitive bias that may play a role in the association between mindfulness and depressive symptoms. It refers to an enhanced sensitivity toward symptoms of anxiety, with a belief that these are harmful. Currently, little is known about the mechanisms underpinning the association between mindfulness, depression, and anxiety sensitivity. The aim of this study was to examine the role of genetic and environmental factors in trait mindfulness, and its genetic and environmental overlap with depressive symptoms and anxiety sensitivity.

METHODS

Over 2,100 16-year-old twins from a population-based study rated their mindfulness, depressive symptoms, and anxiety sensitivity.

RESULTS

Twin modeling analyses revealed that mindfulness is 32% heritable and 66% due to nonshared environmental factors, with no significant influence of shared environment. Genetic influences explained over half of the moderate phenotypic associations between low mindfulness, depressive symptoms, and anxiety sensitivity. About two-thirds of genetic influences and almost all nonshared environmental influences on mindfulness were independent of depression and anxiety sensitivity.

CONCLUSIONS

This is the first study to show that both genes and environment play an important role in the etiology of mindfulness in adolescence. Future research should identify the specific environmental factors that influence trait mindfulness during development to inform targeted treatment and resilience interventions. Shared genetic liability underpinning the co-occurrence of low mindfulness, depression, and anxiety sensitivity suggests that the biological pathways shared between these traits should also be examined.

Comorbidity Among Dimensions of Childhood Psychopathology: Converging Evidence from Behavior Genetics

In this article, we review evidence from recent behavior genetic studies that examined the covariance among common childhood psychopathological conditions and tested specific hypotheses regarding common and broadband-specific underlying features of childhood psychopathology. Specifically, we review the distinction between internalizing and externalizing disorders, the support for the generalist genes and specialist environments model, negative emotionality as a heritable underlying feature common to both internalizing and externalizing disorders, and daring as a heritable broadband-specific underlying feature that distinguishes externalizing disorders from internalizing disorders. We also discuss the implications of research in the search for specific genes that influence childhood psychopathology and suggest avenues for new research.

Cognitive content specificity in anxiety and depressive disorder symptoms: a twin study of cross-sectional associations with anxiety sensitivity dimensions across development

BACKGROUND

The classification of anxiety and depressive disorders has long been debated and has important clinical implications. The present study combined a genetically sensitive design and multiple time points to investigate cognitive content specificity in anxiety and depressive disorder symptoms across anxiety sensitivity dimensions, a cognitive distortion implicated in both disorders.

METHOD

Phenotypic and genetic correlations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were examined at five waves of data collection within childhood, adolescence and early adulthood in two representative twin studies (n pairs = 300 and 1372).

RESULTS

The physical concerns dimension of anxiety sensitivity (fear of bodily symptoms) was significantly associated with anxiety but not depression at all waves. Genetic influences on physical concerns overlapped substantially more with anxiety than depression. Conversely, mental concerns (worry regarding cognitive control) were phenotypically more strongly associated with depression than anxiety. Social concerns (fear of publicly observable symptoms of anxiety) were associated with both anxiety and depression in adolescence. Genetic influences on mental and social concerns were shared to a similar extent with both anxiety and depression.

CONCLUSIONS

Phenotypic patterns of cognitive specificity and broader genetic associations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were similar at all waves. Both disorder-specific and shared cognitive concerns were identified, suggesting it is appropriate to classify anxiety and depression as distinct but related disorders and confirming the clinical perspective that cognitive therapy is most likely to benefit by targeting cognitive concerns relating specifically to the individual's presenting symptoms across development.

Aetiological overlap between obsessive-compulsive and depressive symptoms: a longitudinal twin study in adolescents and adults

BACKGROUND

Depression is commonly co-morbid with obsessive-compulsive disorder (OCD). However, it is unknown whether depression is a functional consequence of OCD or whether these disorders share a common genetic aetiology. This longitudinal twin study compared these two hypotheses.

METHOD

Data were drawn from a longitudinal sample of adolescent twins and siblings (n = 2651; Genesis 12-19 study) and from a cross-sectional sample of adult twins (n = 4920). The longitudinal phenotypic associations between OCD symptoms (OCS) and depressive symptoms were examined using a cross-lag model. Multivariate twin analyses were performed to explore the genetic and environmental contributions to the cross-sectional and longitudinal relationship between OCS and depressive symptoms.

RESULTS

In the longitudinal phenotypic analyses, OCS at time 1 (wave 2 of the Genesis 12-19 study) predicted depressive symptoms at time 2 (wave 3 of the Genesis 12-19 study) to a similar extent to which depressive symptoms at time 1 predicted OCS at time 2. Cross-sectional twin analyses in both samples indicated that common genetic factors explained 52-65% of the phenotypic correlation between OCS and depressive symptoms. The proportion of the phenotypic correlation due to common non-shared environmental factors was considerably smaller (35%). In the adolescent sample, the longitudinal association between OCS at time 1 and subsequent depressive symptoms was accounted for by the genetic association between OCS and depressive symptoms at time 1. There was no significant environmental association between OCS and later depressive symptoms.

CONCLUSIONS

The present findings show that OCS and depressive symptoms co-occur primarily due to shared genetic factors and suggest that genetic, rather than environmental, effects account for the longitudinal relationship between OCS and depressive symptoms.

Genetic and environmental influences on relationship between anxiety sensitivity and anxiety subscales in children

Anxiety sensitivity, a belief that symptoms of anxiety are harmful, has been proposed to influence development of panic disorder. Recent research suggests it may be a vulnerability factor for many anxiety subtypes. Moderate genetic influences have been implicated for both anxiety sensitivity and anxiety, however, little is known about the aetiology of the relationship between these traits in children. Self-reports of anxiety sensitivity and anxiety symptoms were collected from approximately 300 twin pairs at two time points. Partial correlations indicated that anxiety sensitivity at age 8 was broadly associated with most anxiety subtypes at age 10 (r=0.11-0.17, p<0.05). The associations were largely unidirectional, underpinned by stable genetic influences. Non-shared environment had unique influences on variables. Phenotypic results showed that anxiety sensitivity is a broad predictor of anxiety symptoms in childhood. Genetic results suggest that childhood is a developmental period characterised by genetic stability and time-specific environmental influences on anxiety-related traits.

Phenotypic and genetic structure of anxiety sensitivity in adolescence and early adulthood

Anxiety sensitivity is a risk factor for emotional disorders. The structure of anxiety sensitivity was examined using phenotypic and genetic analyses. Self-reported anxiety sensitivity was measured at three time points from adolescence into young adulthood by 2651 individuals from the G1219 twin study. Confirmatory factor analyses revealed comparable statistical support for anxiety sensitivity models consisting of three or four dimensions across all time points. The three-factor model depicting Physical, Social and Mental anxiety-related concerns was favoured due to greater interpretability and parsimony. Multivariate quantitative genetic analyses supported a hierarchical structure with general genetic (.09-.61) and non-shared environmental (.39-.72) influences acting via a higher-order factor as well as dimension-specific genetic (.09-.21) and non-shared environmental (.23-.68) influences. The findings provide further evidence for a hierarchical structure underlying different dimensions of anxiety sensitivity.

Stable genetic influence on anxiety-related behaviours across middle childhood

We examined the aetiology of anxiety symptoms in an unselected population at ages 7 and 9, a period during which anxiety disorders first begin to develop (mean age at onset is 11 years). Specifically, the aim of the study was to investigate genetic and environmental continuity and change in components of anxiety in middle childhood. Parents of over 3,500 twin pairs completed the Anxiety-Related Behaviours Questionnaire (ARBQ) when twins were 7 and 9 years old. Multivariate-longitudinal analyses were conducted to examine genetic and environmental influences on stability and change in four anxiety scales: Negative Cognition, Negative Affect, Fear and Social Anxiety. We found moderate temporal stability in all four scales from 7 to 9 years (correlations ranging from 0.45 to 0.54) and moderate heritability (average 54%). Both shared and non-shared environmental influences were modest (average 18%–28% respectively). Genetic factors (68%) explained most of the homotypic continuity in anxiety. We show that homotypic continuity of Anxiety-Related Behaviours (i.e. the continuation of one specific type of anxiety over time) was largely driven by genetic factors. In contrast, though more varied, heterotypic continuity between some traits (i.e. the change from one type of anxiety-related behaviour into another over time) was mainly due to shared-environmental factors.

Parental Perceptions of Overprotection: Specific to Anxious Children or Shared Between Siblings?

Parents of children with anxiety disorders (n = 45) and parents of nonclinical children (n = 33) were interviewed regarding the rearing of two children in their family. The purpose of the study was to determine whether overprotective parenting, according to parent report, occurs specifically in the context of relationships with the anxiety-disordered child or whether parents also perceive themselves to be overprotective of the anxious child's sibling. Self-reports of overprotection by parents of anxious children were also compared to self-reports of overprotection by parents of nonclinical children. Mothers in the clinical group were more likely to report that they were more protective of the anxious child than they were to report being either more protective of the sibling or equally protective of both children. Both mothers and fathers in the clinical group were no more likely than nonclinical parents to perceive themselves as being more protective overall than other parents.

Etiologic relationships between anxiety and dimensions of maladaptive perfectionism in young adult female twins

BACKGROUND

Theory and research suggest that maladaptive perfectionism, specifically, concerns about mistakes (CM) and doubts about actions (DA), may be important etiologic and maintenance mechanisms for anxiety and its disorders. However, no studies speaking directly to the origins of the relationship, i.e. what etiologic factors underlie the phenotypic association between anxiety and maladaptive perfectionism, exist. The current study aimed to address this gap in the literature by exploring genetic and environmental relationships between anxiety symptoms and maladaptive perfectionism.

METHODS

The sample consisted of 292 young adult same-sex female twins from the Michigan State University Twin Registry. Anxiety symptoms were assessed by the State Trait Anxiety Inventory-Trait version and an anxiety problems scale derived from the Young Adult Self Report. Maladaptive perfectionism was measured using the CM and DA subscales of the Frost Multidimensional Perfectionism Scale.

RESULTS

Anxiety and maladaptive perfectionism were both moderately heritable, with estimates ranging from. 45 to .66. Moreover, multivariate analyses revealed that genetic factors were primarily responsible for associations between anxiety and maladaptive perfectionism (r(g) =.59-.88).

CONCLUSION

This is the first study to demonstrate the role of genetic factors in the relationship between anxiety and maladaptive perfectionism. Future studies are needed to uncover the specific biologic and genetic factors that contribute to this relationship and to evaluate whether maladaptive perfectionism represents an intermediate trait or risk factor for anxiety.

Patterns of anxiety symptoms in toddlers and preschool-age children: evidence of early differentiation

The degree to which young children's anxiety symptoms differentiate according to diagnostic groupings is under-studied, especially in children below the age of 4 years. Theoretical (confirmatory factor analysis, CFA) and statistical (exploratory factor analysis, EFA) analytical methods were employed to test the hypothesis that anxiety symptoms among 2-3-year-old children from a non-clinical, representative sample would differentiate in a manner consistent with current diagnostic nosology. Anxiety symptom items were selected from two norm-referenced parent-report scales of child behavior. CFA and EFA results suggested that anxiety symptoms aggregate in a manner consistent with generalized anxiety, obsessive-compulsive symptoms, separation anxiety, and social phobia. Multi-dimensional models achieved good model fit and fit the data significantly better than undifferentiated models. Results from EFA and CFA methods were predominantly consistent and supported the grouping of early childhood anxiety symptoms into differentiated, diagnostic-specific categories.

Associations between diurnal preference, sleep quality and externalizing behaviours: a behavioural genetic analysis

BACKGROUND

Certain aspects of sleep co-occur with externalizing behaviours in youth, yet little is known about these associations in adults. The present study: (1) examines the associations between diurnal preference (morningness versus eveningness), sleep quality and externalizing behaviours; (2) explores the extent to which genetic and environmental influences are shared between or are unique to these phenotypes; (3) examines the extent to which genetic and environmental influences account for these associations. method: Questionnaires assessing diurnal preference, sleep quality and externalizing behaviours were completed by 1556 young adult twins and siblings.

RESULTS

A preference for eveningness and poor sleep quality were associated with greater externalizing symptoms [r=0.28 (95% CI 0.23-0.33) and 0.34 (95% CI 0.28-0.39), respectively]. A total of 18% of the genetic influences on externalizing behaviours were shared with diurnal preference and sleep quality and an additional 14% were shared with sleep quality alone. Non-shared environmental influences common to the phenotypes were small (2%). The association between diurnal preference and externalizing behaviours was mostly explained by genetic influences [additive genetic influence (A)=80% (95% CI 0.56-1.01)], as was the association between sleep quality and externalizing behaviours [A=81% (95% CI 0.62-0.99)]. Non-shared environmental (E) influences accounted for the remaining variance for both associations [E=20% (95% CI -0.01 to 0.44) and 19% (95% CI 0.01-0.38), respectively].

CONCLUSIONS

A preference for eveningness and poor sleep quality are moderately associated with externalizing behaviours in young adults. There is a moderate amount of shared genetic influences between the phenotypes and genetic influences account for a large proportion of the association between sleep and externalizing behaviours. Further research could focus on identifying specific genetic polymorphisms common to both sleep and externalizing behaviours.

Genetic and environmental influences on different components of the Pittsburgh Sleep Quality Index and their overlap

STUDY OBJECTIVES

To examine the extent to which genetic and environmental factors influence components of sleep quality; the degree to which these components co-occur; and genetic and environmental influences on this co-occurrence.

DESIGN

Twin study.

SETTING

Population based twin registry across the U.K.

PATIENTS OR PARTICIPANTS

Four hundred twenty monozygotic twins, 773 dizygotic twins, and 363 siblings (mode age = 20 years; range 18 to 27 years).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

The Pittsburgh Sleep Quality Index (PSQI) assessed 7 components of sleep quality which overlap to varying degrees. Genetic influence on individual components ranged from 0% to 47%. The remaining source of variance was non-shared environment, except for "sleep duration", for which shared environmental influences were important. Phenotypic correlations between components ranged from 0.22 to 0.61. Bivariate analyses indicated substantial overlap between genes influencing phenotypes (10 of 15 correlations were > or = 0.69); and in general, genetic influence accounted for roughly half the association (> 40% in 9 of 15 correlations). Non-shared environmental influences were in general less correlated across variables (11 of 15 were < 0.4), but owing to their greater influence on each variable, still accounted for roughly half of each association (> or = 40% in 12 of 15 correlations).

CONCLUSIONS

Genetic and non-shared environmental factors are most important in explaining individual differences with regards to different components of sleep quality, although shared environment may influence sleep duration. The pattern of overlap in the genetic and environmental influences accounting for the associations between components of sleep quality is consistent with that seen in other areas of developmental psychopathology of general genes and specific non-shared environmental influences.

Phenotypic and genetic differentiation of anxiety-related behaviors in middle childhood

BACKGROUND

Anxiety-related behaviors (ARBs) are commonly observed during typical development, yet few studies have investigated their etiology in middle childhood. This study aimed to examine both the phenotypic and genetic differentiation of ARB subtypes within the general population at age 7 and 9. It constituted a follow-up to an earlier study of ARBs in preschool children.

METHODS

We investigated the phenotypic structure of ARBs in a large population-based twin sample, comprising 7,834 twin pairs at age 7 and 3,644 twin pairs at age 9. Quantitative genetic modeling techniques were then used to determine the relative influences of genetic and environmental factors upon different types of ARB and upon the covariation between them.

RESULTS

Factor analysis supported the presence of five ARB factors at both ages: negative cognitions, negative affect, fear, obsessive-compulsive behaviors, and social anxiety. Multivariate genetic analyses revealed significant genetic effects and a small but significant influence of shared environment for all ARB subtypes. There was a moderate level of genetic specificity for each subtype as well as some shared genetic effects. Shared environmental influences correlated highly across all types of ARB, whereas nonshared environmental effects were largely subtype specific.

CONCLUSIONS

The current results suggest that ARBs can be differentiated both phenotypically and genetically within middle childhood, with subtypes reflecting symptom groupings of diagnosable disorders but also aspects of temperament. Although some etiological risk factors lead to a generalized vulnerability to anxiety, others may serve to differentiate between different types of ARBs.

Psychopathy as a clinical and empirical construct

In this review, we focus on two major influences on current conceptualizations of psychopathy: one clinical, with its origins largely in the early case studies of Cleckley, and the other empirical, the result of widespread use of the Hare Psychopathy Checklist-Revised (PCL-R) for assessment purposes. Some investigators assert that the PCL-R, ostensibly based on Cleckley's work, has "drifted" from the construct described in his Clinical Profile. We evaluate this profile, note its basis in an unrepresentative sample of patients, and suggest that its literal and uncritical acceptance by the research community has become problematical. We also argue that the idea of construct "drift" is irrelevant to current conceptualizations of psychopathy, which are better informed by the extensive empirical research on the integration of structural, genetic, developmental, personality, and neurobiological research findings than by rigid adherence to early clinical formulations. We offer some suggestions for future research on psychopathy.

Anxiety Disorders in Childhood: Casting a Nomological Net

Empirical research highlights the need for improving the childhood anxiety disorder diagnostic classification system. In particular, inconsistencies in the stability estimates of childhood anxiety disorders and high rates of comorbidity call into the question the utility of the current DSM criteria. This paper makes a case for utilizing a nomological net model for advancing the understanding of childhood anxiety disorders. In this article, we discuss measurement and assessment issues related to improving the childhood anxiety disorder diagnostic system and show how these issues can be addressed by employing the nomological net of childhood anxiety. Because employing the nomological net involves drawing from etiological process theories to facilitate classification and assessment, an integrative model of childhood anxiety disorders is presented as a tentative heuristic. Then evidence for the existing symptom sets is discussed in the context of how process theory mechanisms may be utilized to improve classification and assessment. Testable hypotheses are presented. Measurement, disorder definition, treatment, and policy implications are also discussed.

Parent-child interactions in clinically anxious children and their siblings

Observed 57 children (37 anxiety-disordered and 20 non-clinic-referred children) and their siblings interacting with their parents while completing a complex puzzle task. Consistent with previous findings, mothers were more involved and more intrusive during the task with their anxiety-disordered child than mothers of non-clinic-referred children. Mothers in the clinic-referred group were also significantly more involved and more intrusive during interactions with the anxious child's sibling than mothers of non-clinic-referred children. Although fathers were more involved during the task than mothers overall, no significant differences in overinvolvement were found between fathers of anxiety-disordered children and fathers of non-clinic-referred children. Both mothers and fathers were equally involved with the anxious child and the sibling of the anxious child. Although this study provides support for the association between maternal overinvolvement and the anxiety disorders, it suggests that overinvolvement does not occur exclusively in the context of relationships with the anxiety-disordered child.

The development and modification of temperamental risk for anxiety disorders: prevention of a lifetime of anxiety?

This review poses the question, is it possible to prevent the development of anxiety disorders through selective interventions? The article begins with a review of the major psychosocial risk factors for anxiety disorders. Evidence is reviewed to support the role of inhibited temperament, parent anxiety, environmental support of avoidant coping, and vicarious and instructional learning of avoidance as risks for anxiety. It is argued that the central focus of these risks is an inhibited temperament and that the other risk factors are likely to be both moderated and mediated by this temperamental style. Thus, a clear option for prevention would be to modify early inhibition. Some preliminary data are presented from the Macquarie University Preschool Intervention Project, a longitudinal study of a brief parent education program for the reduction of inhibited temperament in preschool children. Although there remains considerable room for stronger effects, preliminary results show clear promise that it may be possible to modify early risk for anxiety disorders.

Non-associative fear acquisition: a review of the evidence from retrospective and longitudinal research

It is axiomatic that the capacity to experience fear is adaptive, enabling rapid and energetic response to imminent threat or danger. Despite the generally accepted utility of functional fear, the nature of maladaptive fear remains controversial. There is still no consensus about how specific fears and phobias are acquired and modulated. Two major schools of thought are apparent: those suggesting dysfunctional fear arises largely as the result of associative-conditioning processes versus those who favour more biologically based etiological explanations. In this regard, the non-associative model of fear acquisition postulates the existence of a limited number of innate, evolutionary-relevant fears, while emphasising conditioning modes of onset for evolutionary-neutral fears. Recent retrospective and longitudinal studies have tested predictions from the non-associative model. In general, findings support non-associative hypotheses and are difficult to reconcile with neo-conditioning explanations of fear acquisition. These data suggest that four pathways to fear may provide the most parsimonious theory of fear etiology. The theoretical and practical implications of adding a fourth, non-associative path to Rachman's (Behav. Res. Ther. (1977) 15, 375-387) three 'associative' pathways are discussed. Unresolved issues requiring further investigation are considered.

Evidence for a genetic etiology of early-onset delinquency

Age at onset of antisocial behavior discriminates persistent and transitory offenders. The authors proposed that early-onset delinquency has an underlying genetic influence that manifests in problems related to inhibition, whereas late-onset delinquency is more environmentally mediated. To test these notions, they selected 36 early starters, 86 late starters, and 25 nondelinquent controls from a large sample of 11-year-old twins and compared them on several measures related to inhibition and a peer group measure. As expected, early starters had more psychological, behavioral, and emotional problems related to inhibition than late starters and controls. A longitudinal analysis indicated an increase an antisocial behavior among peers of late starters shortly before their delinquency onset. Family history data and a twin analysis provided evidence of greater genetic influence on early-onset than late-onset delinquency.

Plato versus Aristotle: categorical and dimensional models for common mental disorders

There are two quite different ways of conceptualizing common mental disorders: as categorically distributed or as dimensions. In the former case, individuals with "subthreshold" disorders may contain a small proportion of "true cases"; while in the latter, they are seen as having the same basic disorder, but in insufficient degree to warrant a diagnostic label. The categorical school postulates the phenomenon of "comorbidity" to account for those who are both depressed and anxious. The dimensional school regards them as cases of "anxious depression," and observes that the 2 dimensions are highly correlated with one another. This article considers 3 levels of severity of cases satisfying research diagnostic criteria for depression: mild, moderate, and severe. At ascending levels of initial severity, there is increasing disability, and a worse outcome at 12 months. The only positive treatment effect is that favoring antidepressants over sedatives at 3 months, and this effect is related to initial severity-being much greater for the "severe" group of depressions. Initial severity is linearly related to disability, and there is no disjunction at the usual division between "non-cases" and "cases" of depression. Clinicians are obliged to use categorical concepts, as they must decide who is sufficiently ill to justify treatment. But in our efforts to understand the relationships between social and biological variables, dimensional models are far more appropriate.