The Mid-Atlantic Twin Registry, revisited

Genetic and environmental influences on alpha amylase stress reactivity and shared genetic covariation with cortisol

Salivary alpha amylase (sAA) is a common measure of stress reactivity, primarily reflecting sympathetic nervous system activity. Salivary cortisol is also a reliable, frequently used biomarker of stress and reflects the hypothalamic-pituitary-adrenal (HPA) axis response. This study examined heritability across varying metrics of sAA in response to a social evaluative stressor, the Trier Social Stress Test (TSST). The goal of this study was to estimate genetic and environmental influences on measurements of sAA stress reactivity. Moreover, we evaluated the shared genetic covariation between sAA and cortisol. Participants included twins aged 15-20 years (54% female). We measured alpha amylase and cortisol reactivity to the TSST via serial salivary cortisol samples collected pre- and post-TSST. Modest to moderate heritability estimates (11-64%) were observed across measures purported to capture alpha amylase stress reactivity (peak, area under the curve, baseline-to-peak change). Findings also indicate that sAA baseline and peak are primarily influenced by a shared genetic factor. There was no evidence of shared genetic influences between sAA and cortisol. These findings suggest the genetic control of the HPA and Sympathetic Adreno-Medullar axis are genetically independent of one another despite both playing a role in response to stressors.

Leveraging a genetically-informative study design to explore depression as a risk factor for type 2 diabetes: Rationale and participant characteristics of the Mood and Immune Regulation in Twins Study

Background

Comorbidity between depression and type 2 diabetes is thought to arise from the joint effects of psychological, behavioral, and biological processes. Studies of monozygotic twins may provide a unique opportunity for clarifying how these processes inter-relate. This paper describes the rationale, characteristics, and initial findings of a longitudinal co-twin study aimed at examining the biopsychosocial mechanisms linking depression and risk of diabetes in mid-life.

Methods

Participants in the Mood and Immune Regulation in Twins (MIRT) Study were recruited from the Mid-Atlantic Twin Registry. MIRT consisted of 94 individuals who do not have diabetes at baseline, representing 43 twin pairs (41 monozygotic and 2 dizygotic), one set of monozygotic triplets, and 5 individuals whose co-twin did not participate. A broad set of variables were assessed including psychological factors (e.g., lifetime history major depression (MD)); social factors (e.g., stress perceptions and experiences); and biological factors, including indicators of metabolic risk (e.g., BMI, blood pressure (BP), HbA1c) and immune functioning (e.g., pro- and anti-inflammatory cytokines), as well as collection of RNA. Participants were re-assessed 6-month later. Intra-class correlation coefficients (ICC) and descriptive comparisons were used to explore variation in these psychological, social, and biological factors across time and within pairs.

Results

Mean age was 53 years, 68% were female, and 77% identified as white. One-third had a history of MD, and 18 sibling sets were discordant for MD. MD was associated with higher systolic (139.1 vs 132.2 mmHg, p=0.05) and diastolic BP (87.2 vs. 80.8 mmHg, p=0.002) and IL-6 (1.47 vs. 0.93 pg/mL, p=0.001). MD was not associated with BMI, HbA1c, or other immune markers. While the biological characteristics of the co-twins were significantly correlated, all within-person ICCs were higher than the within-pair correlations (e.g., HbA1c within-person ICC=0.88 vs. within-pair ICC=0.49; IL-6 within-person ICC=0.64 vs. within-pair=0.54). Among the pairs discordant for MD, depression was not substantially associated with metabolic or immune markers, but was positively associated with stress.

Conclusions

Twin studies have the potential to clarify the biopsychosocial processes linking depression and diabetes, and recently completed processing of RNA samples from MIRT permits future exploration of gene expression as a potential mechanism.

Genetic and environmental influences on cortisol reactivity to a psychosocial stressor in adolescents and young adults

Individuals vary in their response to psychological and physiological stressors, and this reactivity can be captured using measures of cortisol. Previous research suggests cortisol reactivity is under some degree of genetic control; however, the measures used have varied widely. This study (N = 524) examined potential differences in heritability across varying cortisol metrics of stress reactivity following the Trier Social Stress Test (TSST) and whether these measures are genetically or environmentally interrelated. Participants included twins aged 15-20 years (56% female). Cortisol reactivity to the TSST was assessed via serial salivary cortisol samples collected pre- and post-TSST. Modest to moderate heritability estimates (12% [95CI: 1-36%] - 45% [95CI: 16-69%]) were observed across measures purported to capture stress reactivity (peak, area under the curve [AUC], baseline-to-peak change). Findings also demonstrate both shared and unique genetic and environmental influences between baseline cortisol and cortisol reactivity. Minimal to no additional genetic innovations above and beyond the contributions of peak cortisol were found for other measures of cortisol reactivity such as AUC. This study is one of the largest twin-based samples to examine the heritability of cortisol reactivity, and results suggest that simpler measures of cortisol reactivity demonstrate higher heritability compared to more complex measurements.

An epigenome-wide association study of early-onset major depression in monozygotic twins

Major depression (MD) is a debilitating mental health condition with peak prevalence occurring early in life. Genome-wide examination of DNA methylation (DNAm) offers an attractive complement to studies of allelic risk given it can reflect the combined influence of genes and environment. The current study used monozygotic twins to identify differentially and variably methylated regions of the genome that distinguish twins with and without a lifetime history of early-onset MD. The sample included 150 Caucasian monozygotic twins between the ages of 15 and 20 (73% female; Mage = 17.52 SD = 1.28) who were assessed during a developmental stage characterized by relatively distinct neurophysiological changes. All twins were generally healthy and currently free of medications with psychotropic effects. DNAm was measured in peripheral blood cells using the Infinium Human BeadChip 450 K Array. MD associations with early-onset MD were detected at 760 differentially and variably methylated probes/regions that mapped to 428 genes. Genes and genomic regions involved neural circuitry formation, projection, functioning, and plasticity. Gene enrichment analyses implicated genes related to neuron structures and neurodevelopmental processes including cell-cell adhesion genes (e.g., PCDHA genes). Genes previously implicated in mood and psychiatric disorders as well as chronic stress (e.g., NRG3) also were identified. DNAm regions associated with early-onset MD were found to overlap genetic loci identified in the latest Psychiatric Genomics Consortium meta-analysis of depression. Understanding the time course of epigenetic influences during emerging adulthood may clarify developmental phases where changes in the DNA methylome may modulate individual differences in MD risk.

Genetic and environmental risk structure of internalizing psychopathology in youth

BACKGROUND

Internalizing disorders (IDs), consisting of syndromes of anxiety and depression, are common, debilitating conditions often beginning early in life. Various trait-like psychological constructs are associated with IDs. Our prior analysis identified a tripartite model of Fear/Anxiety, Dysphoria, and Positive Affect among symptoms of anxiety and depression and the following constructs in youth: anxiety sensitivity, fearfulness, behavioral activation and inhibition, irritability, neuroticism, and extraversion. The current study sought to elucidate their overarching latent genetic and environmental risk structure.

METHODS

The sample consisted of 768 juvenile twin subjects ages 9-14 assessed for the nine, abovementioned measures. We compared two multivariate twin models of this broad array of phenotypes.

RESULTS

A hypothesis-driven, common pathway twin model reflecting the tripartite structure of the measures were fit to these data. However, an alternative independent pathway model provided both a better fit and more nuanced insights into their underlying genetic and environmental risk factors.

CONCLUSIONS

Our findings suggest a complex latent genetic and environmental structure to ID phenotypes in youth. This structure, which incorporates both clinical symptoms and various psychological traits, informs future phenotypic approaches for identifying specific genetic and pathophysiological mechanisms underlying ID risk.

The Mid-Atlantic Twin Registry of Virginia Commonwealth University

The Mid-Atlantic Twin Registry (MATR) is a population-based registry of more than 60,000 twins primarily born or living in Virginia, North Carolina and South Carolina. Researchers may utilize the MATR for administration of research services, including study recruitment, data or sample (e.g., DNA) collection, archival dataset creation, as well as data collection through mailed, phone or online surveys. In addition, the MATR houses the MATR Repository, with over 1700 DNA samples primarily from whole blood available for researchers interested in DNA genotyping. For over 40 years MATR twins have participated in research studies with investigators from a range of scientific disciplines and institutions. These studies, which have resulted in numerous publications, explored diverse topics, including substance use, smoking behaviors, developmental psychopathology, bullying, children's health, cardiovascular disease, cancer, the human microbiome, epigenetics of aging, children of twins and sleep homeostasis. Researchers interested in utilizing twins are encouraged to contact the MATR to discuss potential research opportunities.

Genetic underpinnings of callous-unemotional traits and emotion recognition in children, adolescents, and emerging adults

BACKGROUND

Callous-Unemotional (CU) and psychopathic traits are consistently associated with impaired recognition of others' emotions, specifically fear and sadness. However, no studies have examined whether the association between CU traits and emotion recognition deficits is due primarily to genetic or environmental factors.

METHODS

The current study used data from 607 Caucasian twin pairs (N = 1,214 twins) to examine the phenotypic and genetic relationship between the Inventory of Callous-Unemotional Traits (ICU) and facial emotion recognition assessed via the laboratory-based Facial Expression Labeling Task (FELT).

RESULTS

The uncaring/callous dimension of the ICU was significantly associated with impaired recognition of happiness, sadness, fear, surprise, and disgust. The unemotional ICU dimension was significantly associated with improved recognition of surprise and disgust. Total ICU score was significantly associated with impaired recognition of sadness. Significant genetic correlations were found for uncaring/callous traits and distress cue recognition (i.e. fear and sadness). The observed relationship between uncaring/callous traits and deficits in distress cue recognition was accounted for entirely by shared genetic influences.

CONCLUSIONS

The results of the current study replicate previous findings demonstrating impaired emotion recognition among youth with elevated CU traits. We extend these findings by replicating them in an epidemiological sample not selected or enriched for pathological levels of CU traits. Furthermore, the current study is the first to investigate the genetic and environmental etiology of CU traits and emotion recognition, and results suggest genetic influences underlie the specific relationship between uncaring/callous traits and distress cue (fear/sadness) recognition in others.

The genetic and environmental structure of fear and anxiety in juvenile twins

Fear and anxiety are conceptualized as responses to acute or potential threat, respectively. Adult twin studies found substantial interplay between genetic and environmental factors influencing fear disorders (phobias) and anxiety disorders. Research in children, however, has largely examined these factors independently. Thus, there exists a substantial knowledge gap regarding the underlying etiologic structure of these closely-related constructs during development. Symptom counts for five fear (criticism, the unknown, death, animal, medical) and four anxiety (generalized, panic, separation, social) dimensions were obtained for 373 twin pairs ages 9-14. Multivariate twin modeling was performed to elucidate the genetic and environmental influences distributed amongst these dimensions. The best fitting model contained one genetic, two familial environmental, and two unique environmental factors shared between fear and anxiety symptoms plus dimension-specific genetic and unique environmental factors. Although several environmental factors were shared between fear and anxiety dimensions, one latent factor accounted for genetic influences across both domains. While adult studies find somewhat distinct etiological differences between anxiety and phobic disorders, the current results suggest that their relative genetic and environmental influences are not as clearly demarcated in children. These etiological distinctions are more nuanced, likely contributing to the highly diffuse symptom patterns seen during development.

The Genetic and Environmental Relationship Between Childhood Behavioral Inhibition and Preadolescent Anxiety

This study uses novel approaches to examine genetic and environmental influences shared between childhood behavioral inhibition (BI) and symptoms of preadolescent anxiety disorders. Three hundred and fifty-two twin pairs aged 9-13 and their mothers completed questionnaires about BI and anxiety symptoms. Biometrical twin modeling, including a direction-of-causation design, investigated genetic and environmental risk factors shared between BI and social, generalized, panic and separation anxiety. Social anxiety shared the greatest proportion of genetic (20%) and environmental (16%) variance with BI with tentative evidence for causality. Etiological factors underlying BI explained little of the risk associated with the other anxiety domains. Findings further clarify etiologic pathways between BI and anxiety disorder domains in children.

Fear-potentiated startle response as an endophenotype: Evaluating metrics and methods for genetic applications

The modulation of the startle response (SR) by threatening stimuli (fear-potentiated startle; FPS) is a proposed endophenotype for disorders of the fearful-fearlessness spectrum. FPS has failed to show evidence of heritability, raising concerns. However, metrics used to index FPS-and, importantly, other conditional phenotypes that are dependent on a baseline-may not be suitable for the approaches used in genetic epidemiology studies. Here, we evaluated multiple metrics of FPS in a population-based sample of preadolescent twins (N = 569 from 320 twin pairs, M_age = 11.4) who completed a fear-conditioning paradigm with airpuff-elicited SR on two occasions (~1 month apart). We applied univariate and multivariate biometric modeling to estimate the heritability of FPS using several proposed standardization procedures. This was extended with data simulations to evaluate biases in heritability estimates of FPS (and similar metrics) under various scenarios. Consistent with previous studies, results indicated moderate test-retest reliability (r = 0.59) and heritability of the overall SR (h² = 34%) but poor reliability and virtually no unique genetic influences on FPS when considering a raw or standardized differential score that removes baseline SR. Simulations demonstrated that the use of differential scores introduces bias in heritability estimates relative to jointly analyzing baseline SR and FPS in a multivariate model. However, strong dependency of FPS on baseline levels makes unique genetic influences virtually impossible to detect regardless of methodology. These findings indicate that FPS and other conditional phenotypes may not be well suited to serve as endophenotypes unless such codependency can be disentangled.

Confirmatory factor structure and psychometric properties of the Multidimensional Peer Victimization Scale

The Multidimensional Peer Victimization Scale (MPVS; Mynard & Joseph, 2000) is a 16-item self-report scale that captures peer victimization across four dimensions: physical victimization, verbal victimization, social manipulation, and attacks on property. Performance of the scale has not been evaluated among older adolescents. We examined the factor structure, internal consistency reliability, and performance of the scale in two separate epidemiological U.S. samples representing different age groups: 9-14 year olds (N=610) and 15-17 year olds (N=524). The four-factor structure of the scale was affirmed in both samples, however; there was not metric invariance by gender in the younger age group. The scale and its subscales were found to have good internal consistency. Expected relationships between the MPVS and measures of irritability, anxiety, and depression were affirmed. Results support continued use of the MPVS among child and adolescent samples.

A Developmental Twin Study of Emotion Recognition and Its Negative Affective Clinical Correlates

OBJECTIVE

Youth with psychiatric disorders distinguished by irritability, including depression and associated trait neuroticism, show deficits in the ability to recognize facial expressions of emotion, particularly happiness. However, the contribution of genetic and environmental factors to this ability remains unknown. The present study examined this trait in twins to assess the genetic and environmental influences on face-emotion recognition abilities and their association with irritability, neuroticism, and depression.

METHOD

Child and adolescent twins (N = 957 from 496 families) 9 to 17 years old rated their irritability (on the Affective Reactivity Index), neuroticism (on the Junior Eysenck Personality Questionnaire), and depression (on the Short Mood and Feelings Questionnaire) and completed a face-emotion labeling task. Faces depicting anger, disgust, fear, happiness, sadness, and surprise were morphed with a neutral face, yielding 10 levels of increasing emotional expressivity. Biometrical twin analyses evaluated contributions of genetic and environmental factors to the etiology of face-emotion recognition and its association with irritability, neuroticism, and depression.

RESULTS

Recognition of each emotion was heritable; common and specific sets of genetic factors influenced all emotions and individual emotions, respectively. Irritability, neuroticism, and depression were modestly and negatively correlated with emotion recognition, particularly the recognition of happiness. For irritability and neuroticism, this correlation appeared largely due to genetic factors.

CONCLUSION

This study maps genetic and environmental contributions to face-emotion recognition and its association with irritability, neuroticism, and depression. Findings implicate common genetic factors in deficits regarding the recognition of happiness associated with irritability and neuroticism in childhood and adolescence.

Age-Related Differences in the Structure of Genetic and Environmental Contributions to Types of Peer Victimization

The goal of the present investigation was to clarify and compare the structure of genetic and environmental influences on different types (e.g., physical, verbal) of peer victimization experienced by youth in pre-/early adolescence and mid-/late adolescence. Physical, verbal, social, and property-related peer victimization experiences were assessed in two twin samples (306 pairs, ages 9-14 and 294 pairs, ages 15-20). Cholesky decompositions of individual differences in victimization were conducted, and independent pathway (IP) and common pathway (CP) twin models were tested in each sample. In the younger sample, a Cholesky decomposition best described the structure of genetic and environmental contributors to peer victimization, with no evidence that common additive genetic or environmental factors influence different types of peer victimization. In the older sample, common environmental factors influenced peer victimization types via a general latent liability for peer victimization (i.e., a CP model). Whereas the pre-/early adolescent sample demonstrated no evidence of a shared genetic and environmental structure for different types of peer victimization, the mid-/late adolescent sample demonstrates the emergence of an environmentally-driven latent liability for peer victimization across peer victimization types.

A Population-Based Twin Study of Childhood Irritability and Internalizing Syndromes

Childhood irritability exhibits significant theoretical and empirical associations with depression and anxiety syndromes. The current study used the twin design to parse genetic and environmental contributions to these relationships. Children ages 9-14 from 374 twin pairs were assessed for irritability and symptoms of depression, generalized anxiety, panic, social phobia, and separation anxiety using dimensional self-report instruments. Multivariate structural equation modeling decomposed the correlations between these syndromes into genetic and environmental components to examine shared and specific risk domains. Irritability had significant associations with each internalizing symptom domain. Genetic contributions to irritability are moderately correlated with genetic risk for symptoms of depression, generalized anxiety, and separation anxiety with weaker overlap with the other anxiety syndromes. Familial and specific environmental risk factors explained covariation among syndromes and indicated potential syndrome-specific risk. There is substantial overlap among the genetic and environmental factors that influence individual differences in irritability and those that increase liability for depression and anxiety symptoms in children. These findings deepen the current understanding of childhood internalizing risk factors and provide important implications for syndrome prediction and susceptibility gene discovery efforts.

Resting Heart Rate Variability (HRV) in Adolescents and Young Adults from a Genetically-Informed Perspective

Reduced heart rate variability (HRV) is associated with cardiac morbidity, mortality, and negative psychopathology. Most research concerning genetic influences on HRV has focused on adult populations, with fewer studies investigating the developmental period of adolescence and emerging adulthood. The current study estimated the genetic and environmental contributions to resting HRV in a sample of twins using various HRV time domain metrics to assess autonomic function across two different time measurement intervals (2.5- and 10-min). Five metrics of resting HRV [mean interbeat interval (IBI), the standard deviation of normal IBIs (SDNN), root square mean of successive differences between IBIs (RMSSD), cardiac vagal index (CVI), and cardiac sympathetic index (CSI)] were assessed in 421 twin pairs aged 14-20 during a baseline electrocardiogram. This was done for four successive 2.5-min intervals as well as the overall 10-min interval. Heritability (h²) appeared consistent across intervals within each metric with the following estimates (collapsed across time intervals): mean IBI (h² = 0.36-0.46), SDNN (h² = 0.23-0.30), RMSSD (h² = 0.36-0.39), CVI (h² = 0.37-0.42), CSI (h² = 0.33-0.46). Beyond additive genetic contributions, unique environment also was an important influence on HRV. Within each metric, a multivariate Cholesky decomposition further revealed evidence of genetic stability across the four successive 2.5-min intervals. The same models showed evidence for both genetic and environmental stability with some environmental attenuation and innovation. All measures of HRV were moderately heritable across time, with further analyses revealing consistent patterns of genetic and environmental influences over time. This study confirms that in an adolescent sample, the time interval used (2.5- vs. 10-min) to measure HRV time domain metrics does not affect the relative proportions of genetic and environmental influences.

Genetic and Environmental Contributions of Negative Valence Systems to Internalizing Pathways

The genetic and environmental contributions of negative valence systems (NVS) to internalizing pathways study (also referred to as the Adolescent and Young Adult Twin Study) was designed to examine varying constructs of the NVS as they relate to the development of internalizing disorders from a genetically informed perspective. The goal of this study was to evaluate genetic and environmental contributions to potential psychiatric endophenotypes that contribute to internalizing psychopathology by studying adolescent and young adult twins longitudinally over a 2-year period. This report details the sample characteristics, study design, and methodology of this study. The first wave of data collection (i.e., time 1) is complete; the 2-year follow-up (i.e., time 2) is currently underway. A total of 430 twin pairs (N = 860 individual twins; 166 monozygotic pairs; 57.2% female) and 422 parents or legal guardians participated at time 1. Twin participants completed self-report surveys and participated in experimental paradigms to assess processes within the NVS. Additionally, parents completed surveys to report on themselves and their twin children. Findings from this study will help clarify the genetic and environmental influences of the NVS and their association with internalizing risk. The goal of this line of research is to develop methods for early internalizing disorder risk detection.

Test-retest reliability of the facial expression labeling task

Recognizing others' emotional expressions is vital for socioemotional development; impairments in this ability occur in several psychiatric disorders. Further study is needed to map the development of this ability and to evaluate its components as potential transdiagnostic endophenotypes. Before doing so, however, research is required to substantiate the test-retest reliability of scores of the face emotion identification tasks linked to developmental psychopathology. The current study estimated test-retest reliability of scores of one such task, the facial expression labeling task (FELT) among a sample of twin children (N = 157; ages 9-14). Participants completed the FELT at two visits two to five weeks apart. Participants discerned the emotion presented of faces depicting six emotions (i.e., happiness, anger, sadness, fear, surprise, and disgust) morphed with a neutral face to provide 10 levels of increasing emotional expressivity. The present study found strong test-retest reliability (Pearson r) of the FELT scores across all emotions. Results suggested that data from this task may be effectively analyzed using a latent growth curve model to estimate overall ability (i.e., intercept; r's = 0.76-0.85) and improvement as emotions become clearer (i.e., linear slope; r's = 0.69-0.83). Evidence of high test-retest reliability of this task's scores informs future developmental research and the potential identification of transdiagnostic endophenotypes for child psychopathology. (PsycINFO Database Record

Clinical Correlates of Carbon Dioxide Hypersensitivity in Children

OBJECTIVE

Hypersensitivity to carbon dioxide (CO₂)-enriched air may be a promising risk marker for anxiety disorders. Among adult and adolescent samples, heterogeneity in distress response to the CO₂ challenge task indexes 3 underlying classes of individuals, which distinguish between sustained and acute threat response as markers for internalizing disorders, broadly, and anxiety disorders, specifically. The present study examines latent classes in children's response to the CO₂ challenge task to clarify the association of CO₂ hypersensitivity with anxiety and internalizing symptomatology in childhood.

METHOD

Healthy children from a community twin sample (N = 538; age 9-13 years) rated anxious distress every 2 minutes while breathing air enriched to 7.5% CO₂ for 8 minutes. Latent growth mixture modeling evaluated potential classes of individuals with characteristic trajectories of distress during the task to clarify the association with internalizing disorder symptoms and related traits (e.g., anxiety sensitivity, irritability).

RESULTS

Although all participants reported increased distress during the task, interindividual heterogeneity in distress indexed 3 underlying classes: a consistently low class ("low"), a consistently high class ("high"), and participants who demonstrated markedly increased acute distress ("acute"). Compared to the low class, the high class reported greater internalizing psychopathology, whereas membership in the acute class was associated with experiencing a panic-like event during the task.

CONCLUSION

As in older individuals, 3 distinct trajectories emerged to capture interindividual heterogeneity in children's distress during the CO₂ challenge task. These classes were distinguished by clinical validators that reinforce the association of CO₂ hypersensitivity and internalizing disorder phenotypes in children.

The utility of twins in developmental cognitive neuroscience research: How twins strengthen the ABCD research design

The ABCD twin study will elucidate the genetic and environmental contributions to a wide range of mental and physical health outcomes in children, including substance use, brain and behavioral development, and their interrelationship. Comparisons within and between monozygotic and dizygotic twin pairs, further powered by multiple assessments, provide information about genetic and environmental contributions to developmental associations, and enable stronger tests of causal hypotheses, than do comparisons involving unrelated children. Thus a sub-study of 800 pairs of same-sex twins was embedded within the overall Adolescent Brain and Cognitive Development (ABCD) design. The ABCD Twin Hub comprises four leading centers for twin research in Minnesota, Colorado, Virginia, and Missouri. Each site is enrolling 200 twin pairs, as well as singletons. The twins are recruited from registries of all twin births in each State during 2006-2008. Singletons at each site are recruited following the same school-based procedures as the rest of the ABCD study. This paper describes the background and rationale for the ABCD twin study, the ascertainment of twin pairs and implementation strategy at each site, and the details of the proposed analytic strategies to quantify genetic and environmental influences and test hypotheses critical to the aims of the ABCD study.

Review: Genetic research on alcohol use outcomes in African American populations: A review of the literature, associated challenges, and implications

BACKGROUND AND OBJECTIVES

There have been remarkable advances in understanding genetic influences on complex traits; however, individuals of African descent have been underrepresented in genetic research.

METHODS

We review the limitations of existing genetic research on alcohol phenotypes in African Americans (AA) including both twin and gene identification studies, possible reasons for underrepresentation of AAs in genetic research, the implications of the lack of racially diverse samples, and special considerations regarding conducting genetic research in AA populations.

RESULTS

There is a marked absence of large-scale AA twin studies so little is known about the genetic epidemiology of alcohol use and problems among AAs. Individuals of African descent have also been underrepresented in gene identification efforts; however, there have been recent efforts to enhance representation. It remains unknown the extent to which genetic variants associated with alcohol use outcomes in individuals of European and African descent will be shared. Efforts to increase representation must be accompanied by careful attention to the ethical, legal, and social implications of genetic research. This is particularly true for AAs due to the history of abuse by the biomedical community and the persistent racial discrimination targeting this population.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Lack of representation in genetic studies limits our understanding of the etiological factors that contribute to substance use and psychiatric outcomes in populations of African descent and has the potential to further perpetuate health disparities. Involving individuals of diverse ancestry in discussions about genetic research will be critical to ensure that all populations benefit equally from genetic advances. (Am J Addict 2017;26:486-493).

Latent structure of negative valence measures in childhood

BACKGROUND

Internalizing disorders (IDs), consisting of the syndromes of anxiety and depression, are common, debilitating conditions often having onsets in adolescence. Scientists have developed dimensional self-report instruments that assess putative negative valence system (NVS) trait-like constructs as complimentary phenotypes to clinical symptoms. These include various measures that index temperamental predispositions to IDs and correlate with neural substrates of fear, anxiety, and affective regulation. This study sought to elucidate the overarching structure of putative NVS traits and their relationship to early manifestations of ID symptomatology.

METHODS

The sample consisted of 768 juvenile twin subjects ages 9-13. Together with ID symptoms, extant validated instruments were chosen to assess a broad spectrum of NVS traits: anxiety sensitivity, irritability, fearfulness, behavioral activation and inhibition, and neuroticism and extraversion. Exploratory and confirmatory factor analyses (EFA/CFA) were used to investigate the latent structure of the associations among these different constructs and ID symptoms. Bifactor modeling in addition to standard correlated-factor analytic approaches were applied.

RESULTS

Factor analyses produced a primary tripartite solution comprising anxiety/fear, dysphoria, and positive affect among all these measures. Competing DSM-like correlated factors and an RDoC-like NVS bifactor structure provided similar fit to these data.

CONCLUSIONS

Our findings support the conceptual organization of a tripartite latent internalizing domain in developing children. This structure includes both clinical symptoms and a variety of self-report dimensional traits currently in use by investigators. These various constructs are, therefore, most informatively investigated using an inclusive, integrated approach.

Test-retest reliability and validity of a frustration paradigm and irritability measures

BACKGROUND

Data on the reliability and validity of assessments for irritability, particularly behavioral paradigms, are limited. This study examined the test-retest reliability and validity of a frustration paradigm (the Affective Posner 2 task) and two irritability measures [the Affective Reactivity Index (ARI) and Child Behavior Checklist (CBCL) irritability].

METHODS

Participants were 109 youth from a general population sample of twins (aged 9-14 years). Participants completed two visits that were 2-4 weeks apart. At both visits, participants completed the Affective Posner 2 task and self-reported their irritability using the ARI. Parents reported their child's irritability using the ARI and completed the CBCL.

RESULTS

The Affective Posner 2 task demonstrated good test-retest reliability, with intraclass correlations (ICCs) ranging from .44 to .78. The task effectively evoked negative affect (frustration and unhappiness) at both test and retest, demonstrating its construct validity. Moreover, self-rated frustration and unhappiness during the frustration components of the task correlated positively with self-reported but not parent-reported irritability, providing modest support for convergent validity. Parent- and child-reports of the ARI and parent-reports of the CBCL irritability measure showed excellent test-retest reliability, with ICCs ranging from .88 to .90.

LIMITATIONS

The sample consists of mostly twins aged 9-14 years from the communities. Thus, results may not generalize to non-twin samples or clinical samples outside of this age range.

CONCLUSIONS

The Affective Posner 2 paradigm and the ARI and CBCL irritability scales may be useful tools for longitudinal or treatment research on irritability.

Clinical characteristics of latent classes of CO2 hypersensitivity in adolescents and young adults

Although breathing CO₂-enriched air reliably increases anxiety, there is debate concerning the nature and specificity of CO₂ hypersensitivity to panic risk and panic disorder versus anxiety disorders and related traits broadly, particularly among adolescents and emerging adults. The present study sought to clarify the association of CO₂ hypersensitivity with internalizing conditions and symptoms among adolescents and young adults. Participants (N = 628) self-reported anxiety levels every 2 min while breathing air enriched to 7.5% CO₂ for 8 min. Growth mixture models were used to examine the structure of anxiety trajectories during the task and the association of each trajectory with dimensional and diagnostic assessments of internalizing disorders. Three distinct trajectories emerged: overall low (low), overall high (high), and acutely increased anxiety (acute). Compared to the low class, the acute class reported elevated neuroticism, anxiety sensitivity, and stress whereas the high class reported elevated anxiety symptoms, depression symptoms, neuroticism, anxiety sensitivity, and increased likelihood of an anxiety disorder diagnosis. Moreover, the acute and high classes reported experiencing a panic-like event at a higher rate than the low class while participants in the high class terminated the task prematurely at a higher rate. The present study clarifies the nature of response to CO₂ challenge. Three distinct response profiles emerged, which clarifies the manifestation of CO₂ hypersensitivity in anxiety disorders with strong, though not unique, associations with panic-relevant traits.

The Inventory of Callous-Unemotional Traits (ICU) in Children: Reliability and Heritability

Callous-unemotional (CU) traits comprise the core symptoms of psychopathy, yet no study has estimated the heritability of CU traits in a community sample of children using an instrument designed solely to assess CU traits. The current study uses data from 339 twin pairs aged 9-14 to examine the reliability and heritability of the parent-report Inventory of Callous-unemotional Traits (ICU) at two assessments approximately 3 weeks apart. Time-specific measurement error was taken into account to obtain a more accurate estimate of the heritability reflecting the latent liability to CU traits. Test-retest reliability was 0.84 and heritability at visit 1 was 39%. The heritability of the latent liability to CU traits was 47%. This latent liability contributed 79% of the variance in ICU score at visit 1 and visit 2. This is the first study to account for measurement error while examining the heritability of CU traits, furthering our understanding of psychopathy in children.

The Twin Study of Negative Valence Emotional Constructs

The Twin Study of Negative Valence Emotional Constructs is a multi-site study designed to examine the relationship between a broad selection of potential measures designed to assess putative endophenotypes for negative valence systems (NVS) and early symptoms of internalizing disorders (IDs). In this article, we describe the sample characteristics, data collection protocols, and measures used. Pre-adolescent Caucasian twin pairs were recruited through the Mid-Atlantic Twin Registry; data collection began in February of 2013. Enrolled twins completed various dimensional self-report measures along with cognitive, emotional, and psychophysiological tasks designed to assess NVS function. Parents also completed surveys about their twins and themselves. In addition, a subset of the twins also participated in a neuroimaging protocols. Data collection is in the final stages, and preliminary analyses are underway. The findings will potentially expand our understanding of the mechanisms by which genetic and environmental factors contribute to individual differences in NVS phenotypes and provide new insights into underlying risk factors for IDs.

Contemporary views on the genetics of anorexia nervosa

Anorexia nervosa (AN) is a serious mental illness characterized by severe dietary restriction that leads to high rates of morbidity, chronicity, and mortality. Unfortunately, effective treatment is lacking and few options are available. High rates of familial aggregation and significant heritability suggested that the complex etiology of AN is affected by both genetic and environmental factors. In this paper, we review studies that reported common and rare genetic variation that influence susceptibility of AN through candidate gene studies, genome-wide association studies, and sequencing-based studies. We also discuss gene expression, methylation, imaging genetics, and pharmacogenetics to demonstrate that these studies have collectively advanced our knowledge of how genetic variation contributes to AN susceptibility and clinical course. Lastly, we highlight the importance of gene by environment interactions (G×E) and share our enthusiasm for the use of nutritional genomic approaches to elucidate the interaction among nutrients, metabolic intermediates, and genetic variation in AN. A deeper understanding of how nutrition alters genome stability, how genetic variation influences uptake and metabolism of nutrients, and how response to food components affects disordered eating, will lead to personalized dietary interventions and effective nutraceutical and pharmacological treatments for AN.

The CODATwins Project: The Cohort Description of Collaborative Project of Development of Anthropometrical Measures in Twins to Study Macro-Environmental Variation in Genetic and Environmental Effects on Anthropometric Traits

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

Use of an electronic medical record to create the marshfield clinic twin/multiple birth cohort

Population-based genetic analyses, such as the Genome-Wide Association Study (GWAS), have proven powerful for describing the genetic complexities of common disease in epidemiologic research. However, the significant challenges faced by population-based study designs have resulted in revitalization of family-based approaches, including twin studies. Twin studies are unique in their ability to ascertain both heritable and environmental contributions to human disease. Several regional and national twin registries have been constructed using a variety of methods to identify potential twins. A significant challenge in constructing these large twin registries includes the substantial resources required to recruit participants, collect phenotypic data, and update the registries as time progresses. Here we describe the use of the Marshfield Clinic electronic medical record (EMR) to identify a cohort of 19,226 patients enriched for twins or multiples. This cohort defines the Marshfield Clinic Twin/Multiple Birth Cohort (MCTC). An EMR system provides both a mechanism to identify potential twins and a source of detailed phenotypic data in near real time without the need for patient contact outside standard medical care. To demonstrate that the MCTC can be used for genetic-based epidemiologic research, concordance rates for muscular dystrophy (MD) and fragile-X syndrome-two highly heritable diseases-were assessed. Observations indicate that both MD and fragile-X syndrome are highly correlated among affected twins in the MCTC (P ≅ 3.7 × 10(-6) and 1.1 × 10(-4) , respectively). These findings suggest that EMR systems may not only be an effective resource for predicting families of twins, but can also be rapidly applied to epidemiologic research.

Lindon J. Eaves, Ph.D., M.A. (Oxon), D.Sc. Theory-model-data

We begin this special issue by providing a glimpse into the career of Dr. Lindon J. Eaves, from the perspectives of a student, postdoc, instructor, assistant to associate and full professor over the last 20 odd years. We focus primarily on Lindon's contributions to methodological issues and research designs to address them, in particular those related to models for extended twin-family designs, for the development of adolescent behavior, for genotype-environment covariation and interaction, and their application to the Virginia 30,000 and the Virginia Twin Study of Adolescent Behavioral Development. We then introduce the collection of papers in this special festschrift issue of Behavior Genetics, celebrating Dr. Eaves achievements over the last 40 years.

Heritability of DUI convictions: a twin study of driving under the influence of alcohol

BACKGROUND

The study was undertaken to assess the relative contributions of genetic and environmental influences on drunk-driving.

METHODS

Driving records of a cohort of male and female twins (N = 17,360) from the Mid-Atlantic Twin Registry were examined. Structural equation models were used to estimate the magnitude of genetic and environmental effects on male and female phenotypes, and test for gender differences.

RESULTS

There were significant gender and age effects. Compared with females, males were five times more likely to engage in driving under the influence. Among persons aged 21-49 years, the risk for drunk-driving was eight times that for those aged 50+ years and five times greater than those ≤20 years. In both males and females, aged 21-49 years, a large proportion (57%) of the variance in drunk-driving was due to genetic factors and the remaining 43% due to individual specific environmental influences.

CONCLUSIONS

Drunk-driving is under significant genetic influence in both males and females. Our findings suggest that a different set of genes influence DUIs in men and women.