Aberrant Neural Response to Social Exclusion Without Significantly Greater Distress in Youth With Bipolar Disorder: Preliminary Findings

BACKGROUND

Little is known about the effects of social exclusion on youth with bipolar disorder (BD). Understanding these effects and the functional neural correlates of social exclusion in youth with BD may establish differences from healthy youth and help identify areas of intervention.

METHODS

We investigated brain function in 19 youth with BD and 14 age and gender matched healthy control (HC) participants while performing Cyberball, an fMRI social exclusion task. Whole brain activation, region-of-interest, and functional connectivity were compared between groups and examined with behavioral measures.

RESULTS

Compared with the HC group, youth with BD exhibited greater activation in the left fusiform gyrus (FFG) during social exclusion. Functional connectivity between the left FFG and the posterior cingulate/precuneus was significantly greater in the HC compared with the BD group. For the HC group only, age and subjective distress during Cyberball significantly predicted mean FFG activation. No significant differences in distress during social exclusion were found between groups.

CONCLUSION

Although preliminary due to small sample size, these data suggest that youth with BD process social exclusion in a manner that focuses on basic visual information while healthy youth make use of past experiences to interpret current social encounters. This difference may account for the social cognitive issues experienced by youth with BD, which can lead to more severe anxiety and mood symptoms.

Peripheral inflammatory biomarkers define biotypes of bipolar depression

We identified biologically relevant moderators of response to tumor necrosis factor (TNF)-α inhibitor, infliximab, among 60 individuals with bipolar depression. Data were derived from a 12-week, randomized, placebo-controlled clinical trial secondarily evaluating the efficacy of infliximab on a measure of anhedonia (i.e., Snaith-Hamilton Pleasure Scale). Three inflammatory biotypes were derived from peripheral cytokine measurements using an iterative, machine learning-based approach. Infliximab-randomized participants classified as biotype 3 exhibited lower baseline concentrations of pro- and anti-inflammatory cytokines and soluble TNF receptor-1 and reported greater pro-hedonic improvements, relative to those classified as biotype 1 or 2. Pretreatment biotypes also moderated changes in neuroinflammatory substrates relevant to infliximab's hypothesized mechanism of action. Neuronal origin-enriched extracellular vesicle (NEV) protein concentrations were reduced to two factors using principal axis factoring: phosphorylated nuclear factorκB (p-NFκB), Fas-associated death domain (p-FADD), and IκB kinase (p-IKKα/β) and TNF receptor-1 (TNFR1) comprised factor "NEV1," whereas phosphorylated insulin receptor substrate-1 (p-IRS1), p38 mitogen-activated protein kinase (p-p38), and c-Jun N-terminal kinase (p-JNK) constituted "NEV2". Among infliximab-randomized subjects classified as biotype 3, NEV1 scores were decreased at weeks 2 and 6 and increased at week 12, relative to baseline, and NEV2 scores increased over time. Decreases in NEV1 scores and increases in NEV2 scores were associated with greater reductions in anhedonic symptoms in our classification and regression tree model (r² = 0.22, RMSE = 0.08). Our findings provide preliminary evidence supporting the hypothesis that the pro-hedonic effects of infliximab require modulation of multiple TNF-α signaling pathways, including NF-κB, IRS1, and MAPK.

Effects of infliximab on brain neurochemistry of adults with bipolar depression

OBJECTIVES

To explore the relationship between inflammation and neuronal metabolism in bipolar disorder (BD) by evaluating the neurochemical effects of the tumor necrosis factor-α (TNF-α) antagonist infliximab among individuals with bipolar depression METHODS: This is a post-hoc, exploratory analysis from a 12-week, randomized, double-blind, placebo-controlled trial with infliximab for adults with bipolar depression. We assessed the effects of infliximab on concentration of metabolites in the prefrontal cortex, using proton-magnetic resonance spectroscopy (¹H-MRS), as well as its association with clinical outcomes (i.e. depressive symptom severity and cognitive function).

RESULTS

Eighteen participants in the placebo and 15 in the infliximab group were included in this analysis. In the pre-specified primary outcome, there were no significant effects of treatment on prefrontal concentrations of N-acetylaspartate (NAA; p = 0.712). In the secondary analyses, there was a significant treatment by time interaction for glutamate (Glx; p = 0.018), indicating that Glx levels decreased in infliximab-treated patients, relative to placebo. Treatment group significantly moderated the association between changes in Glx levels and changes in a neurocognitive test (i.e. Digit Symbol Substitution Test; p = 0.014), indicating that in infliximab-treated participants reductions in Glx were associated with cognitive improvement.

CONCLUSIONS

Treatment with infliximab did not affect prefrontal NAA concentration in adults with BD. Exploratory analysis suggested a potential effect of treatment on the glutamate system, a finding that should be confirmed and validated by additional studies.

Leptin mediates improvements in cognitive function following treatment with infliximab in adults with bipolar depression

A potential role for leptin in the pathophysiology of bipolar disorder (BD) has been proposed. We recently investigated the effects of the tumor necrosis factor-alpha (TNF-α) antagonist infliximab in individuals with bipolar depression. Leptin is known to interact with the TNF-α system. Herein, we aimed to explore infliximab's effects on leptin and its relationship with brain structure and function. Sixty adults with bipolar depression were enrolled in this randomized, double-blind, 12-week clinical trial of adjunctive infliximab (n = 29) and saline control (n = 31), which were administered intravenously at weeks 0, 2, and 6. Plasma concentrations of leptin, TNF-α and soluble TNF receptors (sTNFR) 1 and 2 were assessed at weeks 0, 2, 6, and 12. We observed a significant decrease in leptin levels in infliximab-treated patients, relative to placebo. Infliximab treatment also significantly reduced TNF-α and sTNFR2, but not sTNFR1 levels. Changes in sTNR2 levels at week 6 significantly determined changes in leptin at week 12 in infliximab-, but not placebo-treated participants. Improvements in verbal memory and increases in global cortical volume were associated with reduction in leptin levels in the treatment group. Mediation analysis indicated that cognitive improvement in infliximab-treated patients was mediated by reductions in leptin levels, which in its turn were determined by decreases in sTNR2 levels. In conclusion, infliximab treatment reduced plasma leptin levels in individuals with BD, through modulation of sTNFR2. Decreases in leptin signaling were associated with an increase in global cortical volume and better performance in a verbal memory task.

Personality and pediatric bipolar disorder: Toward personalizing psychosocial intervention

BACKGROUND

Previous research suggests that challenging temperament characteristics (i.e., low mood, irritability and rigidity) are associated with risk for the development of Pediatric Bipolar Disorder (PBD). This study aimed to investigate the connection between PBD and discrete dimensions of the Five Factor Model (FFM) of personality.

METHODS

Youth diagnosed with PBD I, II, or NOS, at high risk for the disorder (BD-HR) and healthy controls were recruited from the Child and Adolescent Psychiatry Outpatient Clinic at Stanford University School of Medicine. Researchers administered a personality inventory and evaluated current mood state.

RESULTS

BD and BD-HR youth scored lower in Emotional Regulation than did HC youth (F (3, 70) = 10.75, p < .001). Within the BD and BD-HR groups, youth with high depression scores scored lower on Extraversion (F (3, 70) = 8.62, p < .001) and Conscientiousness (F (3, 70) = 4.53, p < .01).

LIMITATIONS

A major limitation of this study is its cross-sectional design, precluding analysis of whether certain traits or clusters of traits predict PBD or other mood disorders.

CONCLUSIONS

Low Emotional Regulation, Conscientiousness, and Agreeableness were associated with PBD; this personality profile clinically corresponds with youth diagnosed with PBD who present with difficulty regulating their emotions, vulnerability to stress, and emotional reactivity. Future research examining personality characteristics in PBD may elucidate further a specific profile to aid clinicians in developing psychosocial interventions for youth with and at high risk of developing PBD.

Extracellular Vesicle Biomarkers Reveal Inhibition of Neuroinflammation by Infliximab in Association with Antidepressant Response in Adults with Bipolar Depression

Accumulating evidence suggests that neuroinflammation is involved in bipolar disorder (BD) pathogenesis. The tumor necrosis factor-alpha (TNF-α) antagonist infliximab was recently reported to improve depressive symptoms in a subpopulation of individuals with BD and history of childhood maltreatment. To explore the mechanistic mediators of infliximab's effects, we investigated its engagement with biomarkers of cellular response to inflammation derived from plasma extracellular vesicles enriched for neuronal origin (NEVs). We hypothesized that infliximab, compared to placebo, would decrease TNF-α receptors (TNFRs) and nuclear factor-kappa B (NF-κB) pathway signaling biomarkers, and that history of childhood abuse would moderate infliximab's effects. We immunocaptured NEVs from plasma samples collected at baseline and at weeks 2, 6, and 12 (endpoint) from 55 participants of this clinical trial and measured NEV biomarkers using immunoassays. A subset of participants (n = 27) also underwent whole-brain magnetic resonance imaging at baseline and endpoint. Childhood physical abuse moderated treatment by time interactions for TNFR1 (χ² = 9.275, p = 0.026), NF-κB (χ² = 13.825, p = 0.003), and inhibitor of NF-κB (IκBα) (χ² = 7.990, p = 0.046), indicating that higher levels of physical abuse were associated with larger biomarker decreases over time. Moreover, the antidepressant response to infliximab was moderated by TNFR1 (χ² = 7.997, p = 0.046). In infliximab-treated participants, reductions in TNFR1 levels were associated with improvement of depressive symptoms, an effect not detected in the placebo group. Conversely, reductions in TNFR1 levels were associated with increased global cortical thickness in infliximab- (r = -0.581, p = 0.029), but not placebo-treated, patients (r = 0.196, p = 0.501). In conclusion, we report that NEVs revealed that infliximab engaged the TNFR/NF-κB neuro-inflammatory pathway in individuals with BD, in a childhood trauma-dependent manner, which was associated with clinical response and brain structural changes.

Immune response to stress induction as a predictor of cognitive-behavioral therapy outcomes in adolescent mood disorders: A pilot study

Cognitive-behavioral therapy (CBT) alleviates symptoms of depression in youth with bipolar disorder (BD) and major depressive disorder (MDD). Empirical research has linked inflammatory markers to depressive symptoms and acute psychosocial stress; however, a gap remains as to whether immune response to stress may serve as a putative mechanism of treatment. This preliminary pilot study determined the modest feasibility of assessing psychobiological response to stress as a predictor of CBT outcomes for youth with mood disorders. We evaluated whether participation in a 10-session group-CBT intervention for mood disorders altered inflammatory response to a laboratory psychosocial stress induction and if this alteration in immune stress responsivity was related to a decrease in depressive symptoms. Thirty-four youth (age M = 15.03, SD = 1.91) diagnosed with BD or MDD participated in a 10-session CBT group and pre- and post-group assessments; twenty-eight participants who completed the group had usable cytokine data. Pre- and post-group assessments included stress induction with the Trier Social Stress Test (TSST) during which inflammatory cytokines were measured at baseline (time 0) and after the TSST at 30, 60, and 90 min. Results suggest it is modestly feasible to measure immune response to stress alongside CBT treatment for adolescent mood disorders. Our findings were mixed; across seven cytokines, hierarchical linear models indicated two cytokines, IL6 and IL12, were sensitive to acute laboratory stress. We also found significant correlations between life stress, inflammation, and depression both pre- and post- CBT group. Inflammation pre-group, as measured by IL12 and IL1 β predicted depressive symptoms following treatment. Although we did not find significant within-subject reductions in inflammation, chronic stress predicted changes in IL β, signaling the central role of chronic stress. This study offers preliminary evidence that immune responsivity to stress induction could serve as a mechanism of treatment for mood disorders in youth, indicating a potential marker for more personalized model of healthcare.

Efficacy of Adjunctive Infliximab vs Placebo in the Treatment of Adults With Bipolar I/II Depression: A Randomized Clinical Trial

IMPORTANCE

To our knowledge, no study has previously evaluated whether individuals with bipolar depression enriched a priori on the basis of biochemical and/or phenotypic immuno-inflammatory activation would differentially respond to an anti-inflammatory agent for the treatment of depressive symptoms.

OBJECTIVE

To assess the antidepressant efficacy of adjunctive infliximab, a monoclonal antibody targeting tumor necrosis factor, in adults with bipolar I and bipolar II depression and inflammatory conditions.

DESIGN, SETTING, AND PARTICIPANTS

This 12-week, randomized, double-blind, placebo-controlled, parallel-group trial of 60 participants was conducted at 2 outpatient tertiary care sites in Canada and the United States. Eligible adults (aged 18-65 years) met DSM-5-defined criteria for bipolar I or bipolar II depression and exhibited pretreatment biochemical and/or phenotypic evidence of inflammatory activation. Participants were enrolled between October 1, 2015, and April 30, 2018. Data analysis was performed from May 1 through July 31, 2018, using modified intent-to-treat analysis.

INTERVENTIONS

Patients were randomized to receive 3 intravenous infusions of infliximab therapy or placebo at baseline and at weeks 2 and 6 of the 12-week study.

MAIN OUTCOMES AND MEASURES

The primary efficacy outcome was baseline-to-end point (ie, week-12) change in Montgomery-Asberg Depression Rating Scale (MADRS) total score. History of childhood maltreatment, as assessed by the Childhood Trauma Questionnaire, was used for exploratory analyses as 1 of several secondary outcomes.

RESULTS

A total of 60 participants were randomized to infliximab (n = 29 [48%]; mean [SD] age, 45.0 [11.7] years; 20 of 28 female [71%]) or to placebo (n = 31 [52%]; mean [SD] age, 46.8 [10.2] years; 26 of 30 female [87%]) across study sites. Overall baseline-to-end point change in MADRS total score was observed across treatment × time interaction (χ2 = 10.33; P = .04); reduction in symptom severity was not significant at week 12 (relative risk, 1.09; 95% CI, 0.80-1.50; df = 1; P = .60). As part of a secondary analysis, a significant treatment × time × childhood maltreatment interaction was observed in which infliximab-treated individuals with childhood history of physical abuse exhibited greater reductions in MADRS total score (χ2 = 12.20; P = .02) and higher response rates (≥50% reduction in MADRS total score) (χ2 = 4.05; P = .04).

CONCLUSIONS AND RELEVANCE

Infliximab did not significantly reduce depressive symptoms compared with placebo in adults with bipolar depression. Results from secondary analyses identified a subpopulation (ie, those reporting physical and/or sexual abuse) that exhibited a significant reduction in depressive symptoms with infliximab treatment compared with placebo.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02363738.

Progressing MoodSwings. The upgrade and evaluation of MoodSwings 2.0: An online intervention for bipolar disorder

MoodSwings 2.0 is a self-guided online intervention for bipolar disorder. The intervention incorporates technological improvements on an earlier validated version of the intervention (MoodSwings 1.0). The previous MoodSwings trial provides this study with a unique opportunity to progress previous work, whilst being able to take into consideration lesson learnt, and technological enhancements. The structure and technology of MoodSwings 2.0 are described and the relevance to other online health interventions is highlighted. An international team from Australia and the US updated and improved the programs content pursuant to changes in DSM-5, added multimedia components and included larger numbers of participants in the group discussion boards. Greater methodological rigour in this trial includes an attention control condition, quarterly telephone assessments, and red flag alerts for significant clinical change. This paper outlines these improvements, including additional security and safety measures. A 3 arm RCT is currently evaluating the enhanced program to assess the efficacy of MS 2.0; the primary outcome is change in depressive and manic symptoms. To our knowledge this is the first randomized controlled online bipolar study with a discussion board attention control and meets the key methodological criteria for online interventions.

Toward a Valid Animal Model of Bipolar Disorder: How the Research Domain Criteria Help Bridge the Clinical-Basic Science Divide

Bipolar disorder is a diagnostically heterogeneous disorder, although mania emerges as a distinct phenotype characterized by elevated mood and increased activity or energy. While bipolar disorder's cyclicity is difficult to represent in animals, models of mania have begun to decode its fundamental underlying neurobiology. When psychostimulants such as amphetamine or cocaine are administered to rodents, a resulting upsurge of motor activity is thought to share face and predictive validity with mania in humans. Studying black Swiss mice, which inherently exhibit proclivity for reward seeking and risk taking, also has yielded some insight. Further, translating the biology of bipolar disorder in humans into animal models has led to greater understanding of roles for candidate biological systems such as the GRIK2 and CLOCK genes, as well as the extracellular signal-related kinase pathway involved in the pathophysiology of the illness. The National Institute of Mental Health Research Domain Criteria initiative seeks to identify building blocks of complex illnesses like bipolar disorder in hopes of uncovering the neurobiology of each, as well as how each fits together to produce syndromes like bipolar disorder or why so many mental illnesses co-occur together. Research Domain Criteria-driven preclinical models of isolated behaviors and domains involved in mania and bipolar disorder will ultimately inform movement toward nosology supported by neurobiology.

A randomized, double-blind, placebo-controlled study of ziprasidone monotherapy in bipolar disorder with co-occurring lifetime panic or generalized anxiety disorder

OBJECTIVE

Bipolar disorder often co-occurs with anxiety disorders. Evidence suggests that second-generation antipsychotics (SGAs) may be useful in treating both conditions. This study examined the efficacy of ziprasidone in the treatment of these disorders.

METHOD

This 3-site, randomized, double-blind, placebo-controlled, parallel group, 8-week trial of ziprasidone monotherapy examined 49 subjects with bipolar disorder and lifetime panic disorder (with or without agoraphobia) or generalized anxiety disorder (GAD) experiencing moderately severe anxiety symptoms at entrance into the study. Both bipolar disorder and anxiety diagnoses were based on DSM-IV-TR criteria. Patients were screened and randomized from June 25, 2010, through August 23, 2011. Primary outcome measures were the Clinical Global Impressions-21 Anxiety Scale (CGI-21 Anxiety) and the Sheehan Disability Scale (SDS), with secondary measures monitoring anxiety and mood symptoms.

RESULTS

Last-observation-carried-forward analyses demonstrated that patients in the ziprasidone group did not improve significantly more than those in the placebo group on the CGI-21 Anxiety (F1 = 0.34; P = .564) or SDS (F1 = 0.26; P = .611). Secondary analysis using hierarchical linear modeling found similar results (CGI-21 Anxiety: F1 = 1.82; P = .178; and SDS: F1 = 0.70; P = .408). Regardless of group, time in the study was associated with significant decrease in anxiety (F1 = 11.08; P = .001) and total disability (F1 = 26.16; P < .001). Patients in the ziprasidone group showed a greater increase in abnormal involuntary movement, and 81.8% (n = 9) of the subjects who withdrew from the study due to adverse events, serious adverse events, or side effects were in the ziprasidone group.

CONCLUSIONS

Results suggest that ziprasidone monotherapy was not associated with a clinically significant improvement in anxiety symptoms or improved function for patients with bipolar disorder, lifetime panic disorder or GAD, and concurrent moderately severe anxiety symptoms, and it was associated with a more negative side-effect profile relative to placebo.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01172652.

Personality dimensions as common and broadband-specific features for internalizing and externalizing disorders

Several researchers have suggested that the nature of the covariation between internalizing and externalizing disorders may be understood better by examining the associations between temperament or personality and these disorders. The present study examined neuroticism as a potential common feature underlying both internalizing and externalizing disorders and novelty seeking as a potential broad-band specific feature influencing externalizing disorders alone. Participants were 12- to 18-year-old twin pairs (635 monozygotic twin pairs and 691 dizygotic twin pairs; 48 % male and 52 % female) recruited from the Colorado Center for Antisocial Drug Dependence. Genetic and nonshared environmental influences shared in common with neuroticism influenced the covariation among distinct internalizing disorders, the covariation among distinct externalizing disorders, and the covariation between internalizing and externalizing disorders. Genetic influences shared in common with novelty seeking influenced the covariation among externalizing disorders and the covariation between major depressive disorder and externalizing disorders, but not the covariation among internalizing disorders or between anxiety disorders and externalizing disorders. Also, after accounting for genetic and environmental influences shared in common with neuroticism and novelty seeking, there were no significant common genetic or environmental influences among the disorders examined, suggesting that the covariance among the disorders is sufficiently explained by neuroticism and novelty seeking. We conclude that neuroticism is a heritable common feature of both internalizing disorders and externalizing disorders, and that novelty seeking is a heritable broad-band specific factor that distinguishes anxiety disorders from externalizing disorders.

Informing DSM-5: biological boundaries between bipolar I disorder, schizoaffective disorder, and schizophrenia

BACKGROUND

The fifth version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) opted to retain existing diagnostic boundaries between bipolar I disorder, schizoaffective disorder, and schizophrenia. The debate preceding this decision focused on understanding the biologic basis of these major mental illnesses. Evidence from genetics, neuroscience, and pharmacotherapeutics informed the DSM-5 development process. The following discussion will emphasize some of the key factors at the forefront of the debate.

DISCUSSION

Family studies suggest a clear genetic link between bipolar I disorder, schizoaffective disorder, and schizophrenia. However, large-scale genome-wide association studies have not been successful in identifying susceptibility genes that make substantial etiological contributions. Boundaries between psychotic disorders are not further clarified by looking at brain morphology. The fact that symptoms of bipolar I disorder, but not schizophrenia, are often responsive to medications such as lithium and other anticonvulsants must be interpreted within a larger framework of biological research.

SUMMARY

For DSM-5, existing nosological boundaries between bipolar I disorder and schizophrenia were retained and schizoaffective disorder preserved as an independent diagnosis since the biological data are not yet compelling enough to justify a move to a more neurodevelopmentally continuous model of psychosis.

Bipolar depression in pediatric populations : epidemiology and management

Depression in children and adolescents with bipolar disorder is more commonly observed than mania or hypomania, and is associated with significant functional disability in multiple environmental realms. Optimal management of pediatric bipolar depression is often defined by its multimodal nature with emphasis on both psychopharmacological and psychosocial treatment. This article provides a brief overview of the epidemiology and clinical course of pediatric bipolar depression, a clinically-oriented guide to the evidence-based psychopharmacological and psychosocial management of bipolar depression in youth, and suggestions on how best to integrate medication and therapy. Recommended treatment for bipolar depression in pediatric populations usually includes both medication and psychosocial interventions given a paucity of double-blind, placebo-controlled psychopharmacological studies. Lithium and lamotrigine are feasible and tentatively efficacious options; however, treatment with quetiapine monotherapy may be no better than placebo. Furthermore, some youth may be at heightened risk for developing manic symptoms after treatment with selective serotonin reuptake inhibitors (SSRIs). Psychotherapy, either alone or adjunctively with medications, provides practitioners with a safe and feasible alternative. Interpersonal and Social Rhythm Therapy for Adolescents (IPSRT-A), Child- and Family-Focused Cognitive Behavioral Therapy (CFF-CBT), Dialectical Behavior Therapy for Adolescents (DBT-A), family psychoeducation, and Family Focused Therapy for Adolescents (FFT-A) are evidence-based treatments available to clinicians treating youth with bipolar depression.

Biological evidence for a neurodevelopmental model of pediatric bipolar disorder

Bipolar disorder (BD) is a chronic illness with high morbidity and mortality. Pediatric onset BD has a more severe course of illness with higher rates of relapse and psychosocial impairment. Discovering interventions early in the course of BD in youth is paramount to preventing full illness expression and improve functioning in these individuals throughout the lifespan. It is therefore important to understand the mechanisms involved in the development of BD in order to determine which youth are at most risk and provide biological targets for early intervention. To serve this cause, we propose a neurodevelopmental model of BD, based on the existing data that implicate prefrontal-subcortical network dysfunction, caused by pre-existing genetic susceptibility and triggered by pathological reactions to stress and chronic inflammatory processes.

Early childhood temperament and the covariation between internalizing and externalizing behavior in school-aged children

There is significant covariation between internalizing and externalizing behavior, although there is also evidence that internalizing behavior is a protective factor against externalizing behavior. Several researchers have posited that the examination of the relationship between temperament or personality and behavior problems may help explain these seemingly contradictory results. Specifically, negative emotionality or neuroticism has been cited as a temperament characteristic that internalizing and externalizing behavior share in common, whereas behavioral inhibition may be related only to internalizing behavior. We examined the degree to which the covariation between internalizing and externalizing behavior assessed from age 4 to 12 years can be explained by temperament characteristics assessed from age 14 to 36 months. Additionally, we assessed the extent to which this relationship is due to genetic or environmental factors, analyzing data from 225 monozygotic and 185 dizygotic twin pairs assessed by the Colorado Longitudinal Twin Study. In males, a portion of the covariation between internalizing and externalizing behavior was explained by shared environmental influences in common with emotionality and shared environmental influences in common with shyness. In females, most of the covariation between internalizing and externalizing behavior was explained by shared environmental influences in common with emotionality. A possible limitation of this study is that the covariation between temperament and behavior problems may be due to shared measurement variance, as parent ratings were used to assess both temperament and behavior problems.