Behavioral disinhibition and the development of substance-use disorders: findings from the Minnesota Twin Family Study

How phenotype and developmental stage affect the genes we find: GABRA2 and impulsivity

CONTEXT

The detection and replication of genes involved in psychiatric outcome has been notoriously difficult. Phenotypic measurement has been offered as one explanation, although most of this discussion has focused on problems with binary diagnoses.

OBJECTIVE

This article focuses on two additional components of phenotypic measurement that deserve further consideration in evaluating genetic associations: (1) the measure used to reflect the outcome of interest, and (2) the developmental stage of the study population. We focus our discussion of these issues around the construct of impulsivity and externalizing disorders, and the association of these measures with a specific gene, GABRA2.

DESIGN, SETTING, AND PARTICIPANTS

Data were analyzed from the Collaborative Study on the Genetics of Alcoholism Phase IV assessment of adolescents and young adults (ages 12-26; N = 2,128).

MAIN OUTCOME MEASURES

Alcohol dependence, illicit drug dependence, childhood conduct disorder, and adult antisocial personality disorder symptoms were measured by psychiatric interview; Achenbach youth/adult self-report externalizing scale; Zuckerman Sensation-Seeking scale; Barratt Impulsivity scale; NEO extraversion and consciousness.

RESULTS

GABRA2 was associated with subclinical levels of externalizing behavior as measured by the Achenbach in both the adolescent and young adult samples. Contrary to previous associations in adult samples, it was not associated with clinical-level DSM symptom counts of any externalizing disorders in these younger samples. There was also association with sensation-seeking and extraversion, but only in the adolescent sample. There was no association with the Barratt impulsivity scale or conscientiousness.

CONCLUSIONS

Our results suggest that the pathway by which GABRA2 initially confers risk for eventual alcohol problems begins with a predisposition to sensation-seeking early in adolescence. The findings support the heterogeneous nature of impulsivity and demonstrate that both the measure used to assess a construct of interest and the age of the participants can have profound implications for the detection of genetic associations.

The effect of general and drug-specific family environments on comorbid and drug-specific problem behavior: a longitudinal examination

Previous research has shown that the development of alcohol and tobacco dependence is linked and that both are influenced by environmental and intrapersonal factors, many of which likely interact over the life course. The present study examines the effects of general and alcohol- and tobacco-specific environmental influences in the family of origin (ages 10-18) and family of cohabitation (ages 27-30) on problem behavior and alcohol- and tobacco-specific outcomes at age 33. General environmental factors include family management, conflict, bonding, and involvement. Alcohol environment includes parental alcohol use, parents' attitudes toward alcohol, and children's involvement in family drinking. Tobacco-specific environment is assessed analogously. Additionally, analyses include the effects of childhood behavioral disinhibition, initial behavior problems, and age 18 substance use. Analyses were based on 469 participants drawn from the Seattle Social Development Project (SSDP) sample. Results indicated that (a) environmental factors within the family of origin and the family of cohabitation are both important predictors of problem behavior at age 33; (b) family of cohabitation influences partially mediate the effects of family of origin environments; (c) considerable continuity exists between adolescent and adult general and tobacco (but not alcohol) environments; age 18 alcohol and tobacco use partially mediates these relationships; and (d) childhood behavioral disinhibition contributed to age 33 outcomes, over and above the effects of family of cohabitation mediators. Implications for preventive interventions are discussed.

Association between P3 event-related potential amplitude and externalizing disorders: a time-domain and time-frequency investigation of 29-year-old adults

This study determined whether time-domain P3 amplitude and time-frequency principal component (TF-PC) reductions are present in adulthood (age 29) when participants have largely passed through the age of heaviest substance misuse. Participants were assessed from age 17 through 29 for lifetime externalizing (EXT) disorders. EEG comparisons from three topographic regions were examined for P3 amplitude and TF-PCs at delta and theta frequency ranges. Significant P3 amplitude reductions were found in those with EXT for both regional and site-Pz analyses, with stronger effects observed the greater the EXT comorbidity. Reductions were also observed in all eight TF-PCs extracted, with a delta component yielding frontal effects not apparent in the time domain. Overall, results suggest that these brain measures continue, at age 29, to provide effective indices of EXT that potentially tap a neural substrate related to behavioral disinhibition.

The Minnesota Center for Twin and Family Research genome-wide association study

As part of the Genes, Environment and Development Initiative, the Minnesota Center for Twin and Family Research (MCTFR) undertook a genome-wide association study, which we describe here. A total of 8,405 research participants, clustered in four-member families, have been successfully genotyped on 527,829 single nucleotide polymorphism (SNP) markers using lllumina's Human660W-Ouad array. Quality control screening of samples and markers as well as SNP imputation procedures are described. We also describe methods for ancestry control and how the familial clustering of the MCTFR sample can be accounted for in the analysis using a Rapid Feasible Generalized Least Squares algorithm. The rich longitudinal MCTFR assessments provide numerous opportunities for collaboration.

Genetic amplification and the individualization of the parent-child relationship across adolescence

BACKGROUND

Many psychological traits become increasingly influenced by genetic factors throughout development, including several that might intuitively be seen as purely environmental characteristics. One such trait is the parent-child relationship, which is associated with a variety of socially significant outcomes, including mental health and criminal behavior. Genetic factors have been shown to partially underlie some of these associations, but the changing role of genetic influence over time remains poorly understood.

METHOD

Over 1000 participants in a longitudinal twin study were assessed at three points across adolescence with a self-report measure regarding the levels of warmth and conflict in their relationships with their parents. These reports were analyzed with a biometric growth curve model to identify changes in genetic and environmental influences over time.

RESULTS

Genetic influence on the child-reported relationship with parent increased throughout adolescence, while the relationship's quality deteriorated. The increase in genetic influence resulted primarily from a positive association between genetic factors responsible for the initial relationship and those involved in change in the relationship over time. By contrast, environmental factors relating to change were negatively related to those involved in the initial relationship.

CONCLUSIONS

The increasing genetic influence seems to be due to early genetic influences having greater freedom of expression over time whereas environmental circumstances were decreasingly important to variance in the parent-child relationship. We infer that the parent-child relationship may become increasingly influenced by the particular characteristics of the child (many of which are genetically influenced), gradually displacing the effects of parental or societal ideas of child rearing.

Quantifying the Association between Personality Similarity and Marital Adjustment Using Profile Correlations: A Cautionary Tale

Profile correlations are sometimes used to quantify personality trait similarity between relationship partners. These coefficients are then used to test whether similar couples are happier couples. The current paper describes several different methods of calculating profile correlations and outlines procedures for testing whether these coefficients are related to marital adjustment in a sample of 1,643 couples. There was little evidence that profile correlations were related to marital adjustment after accounting for normativeness (i.e., the degree to which individual's matched the typical personality profile) and when accounting for each individual's personality attributes. Results suggest that researchers using profile correlations should be cautious given that the interpretation and psychological meaning of results often depend on how the coefficients are calculated.

Tests of a direct effect of childhood abuse on adult borderline personality disorder traits: a longitudinal discordant twin design

We used a longitudinal twin design to examine the causal association between sexual, emotional, and physical abuse in childhood (before age 18) and borderline personality disorder (BPD) traits at age 24 using a discordant twin design and biometric modeling. Additionally, we examined the mediating and moderating effects of symptoms of childhood externalizing and internalizing disorders on the link between childhood abuse and BPD traits. Although childhood abuse, BPD traits, and internalizing and externalizing symptoms were all correlated, the discordant twin analyses and biometric modeling showed little to no evidence that was consistent with a causal effect of childhood abuse on BPD traits. Instead, our results indicate that the association between childhood abuse and BPD traits stems from common genetic influences that, in some cases, also overlap with internalizing and externalizing disorders. These findings are inconsistent with the widely held assumption that childhood abuse causes BPD, and they suggest that BPD traits in adulthood are better accounted for by heritable vulnerabilities to internalizing and externalizing disorders.

Evidence for a Heritable Brain Basis to Deviance-Promoting Deficits in Self-Control

PURPOSE

Classic criminological theories emphasize the role of impaired self-control in behavioral deviancy. Reduced amplitude of the P300 brain response is reliably observed in individuals with antisocial and substance-related problems, suggesting it may serve as a neurophysiological indicator of deficiencies in self-control that confer liability to deviancy.

METHODS

The current study evaluated the role of self-control capacity - operationalized by scores on a scale measure of trait disinhibition - in mediating the relationship between P300 brain response and behavioral deviancy in a sample of adult twins (N=419) assessed for symptoms of antisocial/addictive disorders and P300 brain response.

RESULTS

As predicted, greater disorder symptoms and higher trait disinhibition scores each predicted smaller P300 amplitude, and trait disinhibition mediated observed relations between antisocial/addictive disorders and P300 response. Further, twin modeling analyses revealed that trait disinhibition scores and disorder symptoms reflected a common genetic liability, and this genetic liability largely accounted for the observed phenotypic relationship between antisocial-addictive problems and P300 brain response.

CONCLUSIONS

These results provide further evidence that heritable weaknesses in self-control capacity confer liability to antisocial/addictive outcomes and that P300 brain response indexes this dispositional liability.

Genetic influences on composite neural activations supporting visual target identification

Behavior genetic studies of brain activity associated with complex cognitive operations may further elucidate the genetic and physiological underpinnings of basic and complex neural processing. In the present project, monozygotic (N=51 pairs) and dizygotic (N=48 pairs) twins performed a visual oddball task with dense-array EEG. Using spatial PCA, two principal components each were retained for targets and standards; wavelets were used to obtain time-frequency maps of eigenvalue-weighted event-related oscillations for each individual. Distribution of inter-trial phase coherence (ITC) and single trial power (STP) over time indicated that the early principal component was primarily associated with ITC while the later component was associated with a mixture of ITC and STP. Spatial PCA on point-by-point broad sense heritability matrices revealed data-derived frequency bands similar to those well established in EEG literature. Biometric models of eigenvalue-weighted time-frequency data suggest a link between physiology of oscillatory brain activity and patterns of genetic influence.

The Brisbane Longitudinal Twin Study: Pathways to Cannabis Use, Abuse, and Dependence project-current status, preliminary results, and future directions

We describe the data being collected from the Brisbane Longitudinal Twin Study in Australia as part of the US National Institute on Drug Abuse (NIDA)-funded project, Pathways to Cannabis Use, Abuse and Dependence. The history, recruitment, assessment, and retention of twin families in this project are described in detail, along with preliminary findings and plans for future research. The goal of this NIDA project is to make a significant contribution to the discovery of quantitative trait loci influencing cannabis use disorders. Although the focus is cannabis use, abuse, and dependence in young adults, measures of comorbid illicit drug use disorders are also being collected. In addition, a variety of internalizing and externalizing disorders are being assessed, funded by support from the Australian National Health and Medical Research Council. Because these same twins have participated in numerous twin studies since 1992, future plans will include linking different phenotypes to investigate relationships between drug use, psychiatric disorders, and psychological phenotypes within cross-sectional and longitudinal or developmental frameworks.

Associations between substance use disorders and major depression in parents and late adolescent-emerging adult offspring: an adoption study

AIMS

To examine whether major depressive disorder (MDD) and substance use disorders [SUDs: specifically, nicotine dependence (ND), alcohol use disorders (AUDs), and cannabis use disorders (CUDs)] in parents predicted increased risk for these disorders in late adolescent-emerging adult offspring and, specifically, the extent to which the pattern of risk differed for adopted and non-adopted youth.

PARTICIPANTS

Late adolescent and emerging adult participants from the Sibling Interaction and Behavior Study (mean age = 18.8), a community-based investigation of adopted and non-adopted adolescents, and their parents (adoptive parents of adopted youth, biological parents of non-adopted adolescents) were included.

MEASUREMENTS

Structured interviews were used to assess these disorders.

FINDINGS

(i) When the same disorder in parents and adolescents was examined, parental MDD was associated with increased risk for MDD among both adopted (P < 0.001) and non-adopted (P < 0.01) adolescents; in contrast, SUDs were associated with increased risk for the same SUD in non-adopted offspring (all P < 0.01). (ii) When cross-SUD effects were examined, for the most part, each SUD was associated with increased risk for other SUDs among non-adopted but not adopted offspring (most P < 0.05). (iii) When MDD-SUD associations were examined, parental ND and CUDs predicted increased risk for MDD in non-adopted (P < 0.001), but not adopted, adolescents. These effects tended to remain significant when adjusting for within-person comorbidity (P < 0.05).

CONCLUSIONS

Major depressive disorder in parents appears to be a risk factor for late adolescent-emerging adult major depressive disorder but not substance use disorder in offspring, with this risk being environmentally mediated. Substance use disorder in parents appears, via genetic mediation, to increase risk of substance use disorder in adolescent offspring, and cannabis and nicotine use disorders in parents contribute similarly to major depressive disorder in those offspring.

Comparison of alcohol impairment of behavioral and attentional inhibition

BACKGROUND

Despite the wealth of studies demonstrating the impairing effects of alcohol on behavioral inhibition, less is known regarding effects of the drug on attentional inhibition (i.e., the ability to ignore distracting stimuli in the environment in order to focus attention on relevant information). The current study examined alcohol impairment of both behavioral and attentional inhibition, as well as potential associations between the two mechanisms of inhibitory control.

METHODS

Men (n=27) and women (n=21) performed a measure of behavioral inhibition (cued go/no-go task) and a measure of attentional inhibition (delayed ocular return task) following three doses of alcohol: 0.65 g/kg, 0.45 g/kg, and 0.0 g/kg (placebo).

RESULTS

Alcohol impaired both behavioral and attentional inhibition relative to placebo; however, correlational analyses revealed no associations between measures of behavioral and attentional inhibition following any dose. Additionally, men committed more inhibitory failures on the behavioral inhibition task, whereas women committed more inhibitory failures on the attentional inhibition task.

CONCLUSIONS

These findings suggest that behavioral and attentional inhibition are equally sensitive to the impairing effects of alcohol, yet represent distinct components of inhibitory control. Additionally, the observed gender differences in control of behavior and attention could have important implications regarding negative consequences associated with alcohol-induced disinhibition in men and women.

The Michigan State University Twin Registry (MSUTR): an update

The primary aim of the Michigan State University Twin Registry (MSUTR) is on understanding developmental changes in genetic, environmental, and neurobiological influences on internalizing and externalizing disorders, with antisocial behavior and disordered eating representing our particular areas of interest. The MSUTR has two broad components: a large-scale, population-based registry of child, adolescent, and adult twins and their families (current N ~20,000) and a series of more focused and in-depth studies drawn from the registry (current N ~4,000). Participants in the population-based registry complete a family health and demographic questionnaire via mail. Families are then recruited for one or more of the intensive, in-person studies from the population-based registry based on their answers to relevant items in the registry questionnaire. These in-person assessments target a variety of biological, genetic, and environmental phenotypes, including multi-informant measures of psychiatric and behavioral phenotypes, census and neighborhood informant reports of twin neighborhood characteristics, buccal swab and salivary DNA samples, assays of adolescent and adult steroid hormone levels, and/or videotaped interactions of child twin families. This article provides an overview of the MSUTR and describes current and future research directions.

Decline in genetic influence on the co-occurrence of alcohol, marijuana, and nicotine dependence symptoms from age 14 to 29

OBJECTIVE

Cross-sectional studies have demonstrated high rates of comorbidity among substance use disorders. However, few studies have examined the developmental course of incident comorbidity and how it changes from adolescence to adulthood. The authors examine patterns of comorbidity among substance use disorders to gain insight into the effect of shared versus specific etiological influences on measures of substance abuse and dependence.

METHOD

The authors evaluated the pattern of correlations among nicotine, alcohol, and marijuana abuse and dependence symptom counts as well as their underlying genetic and environmental influences in a community-representative twin sample (N=3,762). Symptoms were assessed at ages 11, 14, 17, 20, 24, and 29 years. A single common factor was used to model the correlations among symptom counts at each age. The authors examined age-related changes in the influence of this general factor by testing for differences in the mean factor loading across time.

RESULTS

Mean levels of abuse or dependence symptoms increased throughout adolescence, peaked around age 20, and declined from age 24 to age 29. The influence of the general factor was highest at ages 14 and 17, but decreased from age 17 to age 24. Genetic influences of the general factor declined considerably with age alongside an increase in nonshared environmental influences.

CONCLUSIONS

Adolescent substance abuse or dependence is largely a function of shared etiology. As young people age, their symptoms are increasingly influenced by substance-specific etiological factors. Heritability analyses revealed that the generalized risk is primarily influenced by genetic factors in adolescence, but nonshared environmental influences increase in importance as substance dependence becomes more specialized in adulthood.

Reconceptualizing antisocial deviance in neurobehavioral terms

We propose that neuroscientific understanding of antisocial behavior can be advanced by focusing programmatic efforts on neurobehavioral trait constructs, that is, individual difference constructs with direct referents in neurobiology as well as behavior. As specific examples, we highlight inhibitory control and defensive reactivity as two such constructs with clear relevance for understanding antisocial behavior in the context of development. Variations in inhibitory control are theorized to reflect individual differences in the functioning of brain systems that operate to guide and inhibit behavior and regulate emotional response in the service of nonimmediate goals. Variations in defensive reactivity are posited to reflect individual differences in the sensitivity of the brain's aversive motivational (fear) system. We describe how these constructs have been conceptualized in the adult and child literatures and review work pertaining to traditional psychometric (rating and behaviorally based) assessment of these constructs and their known physiological correlates at differing ages as well as evidence linking these constructs to antisocial behavior problems in children and adults. We outline a psychoneurometric approach, which entails systematic development of neurobiological measures of target trait constructs through reference to psychological phenotypes, as a paradigm for linking clinical disorders to neurobiological systems. We provide a concrete illustration of this approach in the domain of externalizing proneness and discuss its broader implications for research on conduct disorder, antisocial personality, and psychopathy.

The co-occurring use and misuse of cannabis and tobacco: a review

AIMS

  Cannabis and tobacco use and misuse frequently co-occur. This review examines the epidemiological evidence supporting the life-time co-occurrence of cannabis and tobacco use and outlines the mechanisms that link these drugs to each other. Mechanisms include (i) shared genetic factors; (ii) shared environmental influences, including (iii) route of administration (via smoking), (iv) co-administration and (v) models of co-use. We also discuss respiratory harms associated with co-use of cannabis and tobacco, overlapping withdrawal syndromes and outline treatment implications for co-occurring use.

METHODS

  Selective review of published studies.

RESULTS

  Both cannabis and tobacco use and misuse are influenced by genetic factors, and a proportion of these genetic factors influence both cannabis and tobacco use and misuse. Environmental factors such as availability play an important role, with economic models suggesting a complementary relationship where increases in price of one drug decrease the use of the other. Route of administration and smoking cues may contribute to their sustained use. Similar withdrawal syndromes, with many symptoms in common, may have important treatment implications. Emerging evidence suggests that dual abstinence may predict better cessation outcomes, yet empirically researched treatments tailored for co-occurring use are lacking.

CONCLUSIONS

  There is accumulating evidence that some mechanisms linking cannabis and tobacco use are distinct from those contributing to co-occurring use of drugs in general. There is an urgent need for research to identify the underlying mechanisms and harness their potential etiological implications to tailor treatment options for this serious public health challenge.

Youth appraisals of inter-parental conflict and genetic and environmental contributions to attention-deficit hyperactivity disorder: examination of GxE effects in a twin sample

Identification of gene x environment interactions (GxE) for attention-deficit hyperactivity disorder (ADHD) is a crucial component to understanding the mechanisms underpinning the disorder, as prior work indicates large genetic influences and numerous environmental risk factors. Building on prior research, children's appraisals of self-blame were examined as a psychosocial moderator of latent etiological influences on ADHD via biometric twin models, which provide an omnibus test of GxE while managing the potential confound of gene-environment correlation. Participants were 246 twin pairs (total n = 492) ages 6-16 years. ADHD behaviors were assessed via mother report on the Child Behavior Checklist. To assess level of self-blame, each twin completed the Children's Perception of Inter-parental Conflict scale. Two biometric GxE models were fit to the data. The first model revealed a significant decrease in genetic effects and a significant increase in unique environmental influences on ADHD with increasing levels of self-blame. These results generally persisted even after controlling for confounding effects due to gene-environment correlation in the second model. Results suggest that appraisals of self-blame in relation to inter-parental conflict may act as a key moderator of etiological contributions to ADHD.

Delineating physiologic defensive reactivity in the domain of self-report: phenotypic and etiologic structure of dispositional fear

BACKGROUND

Individual differences in fear and fearlessness have been investigated at their extremes in relation to markedly different forms of psychopathology--anxiety disorders and psychopathy, respectively. A documented neural substrate of fear-related traits and disorders is defensive reactivity as reflected in aversive startle potentiation (ASP).

METHOD

The current study extended prior work by characterizing, in a sample of adult twins from the community (n = 2511), the phenotypic and etiologic structure of self-report measures of fear and fearlessness known to be associated with ASP.

RESULTS

Analyses revealed a hierarchical structure to the trait fear domain, with an overarching, bipolar fear/fearlessness dimension saturating each measure in this domain, and subfactors labeled 'distress,' 'stimulation seeking' and 'sociability' accounting for additional variance in particular measures. The structure of genetic and non-shared environmental associations among the measures closely mirrored the phenotypic structure of the domain.

CONCLUSIONS

The findings have implications for proposals to reconceptualize psychopathology in neurobiological terms.

Index of the transmissible common liability to addiction: heritability and prospective associations with substance abuse and related outcomes

BACKGROUND

Substance use disorders (SUDs) are highly comorbid and exhibit a relatively late onset. As such, many behaviors and personality traits present prior to the initiation of substance use can be used to predict later SUDs. The transmissible liability index (TLI) is a quantitative measure of such behaviors that indexes the common liability to SUDs. We examined the predictive utility and heritability of the TLI in a large community twin sample.

METHODS

Using the Minnesota Twin Family Study (N=2510), we estimated TLI scores from mother, child, and teacher reports of symptom and personality measures assessed at age 11. We then estimated the genetic and environmental contributions to the association between TLI scores at age 11 and composite measures of substance abuse and behavioral disinhibition (antisocial behavior) at age 17.

RESULTS

For both male and female twins, TLI scores were highly heritable (.76) and exhibited moderate associations with adolescent substance abuse (r=.29) and behavioral disinhibition (r=.40). Genetic factors accounted for the association between TLI scores and the adolescent outcomes.

CONCLUSIONS

Findings support the utility of the TLI as a measure of the inherited, common liability to SUDs.

Examining electrodermal hyporeactivity as a marker of externalizing psychopathology: a twin study

Literature suggests that reduced electrodermal reactivity (EDR) is related to externalizing problems. However, the genetic and environmental etiology of this association is unknown. Using a standard habituation paradigm, we measured responses to 15 loud tones in four cohorts of adolescent twins (N = 2,129). We quantified EDR as the average size of elicited responses (amplitude) and by counting the number of skin conductance responses (frequency). Externalizing liability was indexed through a general factor underlying substance-related problems and antisocial behavior. Response frequency, but not mean amplitude, was inversely associated with externalizing liability in each twin cohort. Biometric modeling revealed that most of the overlap between response frequency and externalizing liability was due to genetic influences common to both phenotypes. It is argued that neurological mechanisms involved in habituation may shed light on the etiology of psychopathology.

Longitudinal twin study of borderline personality disorder traits and substance use in adolescence: developmental change, reciprocal effects, and genetic and environmental influences

Although the comorbidity between borderline personality disorder (BPD) and substance abuse is well established, there are few longitudinal studies that have examined its developmental origins or whether the comorbidity is due to common genetic or environmental risk factors. To fill this gap, we used a large sample of female adolescent twins (N = 1,280) to examine the developmental course, reciprocal influences, and the genetic and environmental factors underlying the co-occurrence of BPD traits and substance use from age 14 to 18. Rank-order stability was moderate to high for both BPD traits (r = .58) and substance use (r = .51), whereas mean levels of substance use increased substantially from age 14 to 18 (d = 0.77) and BPD traits showed a small decline (d = -0.21). BPD traits and substance use exhibited concurrent and prospective associations; however, the longitudinal associations dropped to nonsignificance after accounting for the temporal stability of each trait. Twin analyses revealed that shared environmental factors accounted for the association between BPD traits and substance use at age 14, but genetic factors accounted for the association at age 18. These results indicate that, at least in adolescence, the comorbidity between BPD traits and substance use is a consequence of common risk factors rather than due to one being a casual antecedent of the other.

An examination of environmental and genetic contributions to the determinants of suicidal behavior among male twins

The purpose of the present study was to examine the relative association of genetic and environmental factors with individual differences in each of the proximal, jointly necessary, and sufficient causes for suicidal behavior, according to the Interpersonal-Psychological Theory of Suicide (IPTS; Joiner, 2005). We examined data on derived scales measuring acquired capability, belongingness, and burdensomeness (the determinants of suicidal behavior, according to theory) from 348 adolescent male twins. Univariate biometrical models were used to estimate the magnitude of additive genetic (A), non-additive genetic (D), shared environmental (C), and non-shared environmental (E) effects associated with the variance in acquired capability, belongingness, and burdensomeness. The best fitting model for the acquired capability allowed for additive genetic and environmental effects, whereas the best fitting model for burdensomeness and belongingness allowed for shared and non-shared environmental effects. The present research extends prior work by specifying the environmental and genetic contributions to the components of the IPTS, and our findings suggest that belongingness and burdensomeness may be more appropriate targets for clinical intervention than acquired capability as these factors may be more malleable or amenable to change.

Returns to education: what do twin studies control?

The current article examines the assumptions of the MZ co-twin control method that has been applied in attempts to gain more accurate estimates of the returns to education by naturally 'controlling' for individual differences on which MZ twins are matched. The current study examined 1738 MZ and 926 DZ twins from Minnesota, including 133 pairs of MZ and 101 pairs of DZ twins discordant for university attendance. They were assessed prospectively on personality, intelligence, GPA, and academic motivation; a subset also has reported income at age 29. MZ twins discordant for university attendance differed significantly and prospectively on verbal IQ, personality traits, and GPA. While MZ co-twin control studies can provide more accurate estimates of the returns to education than analyses of single individuals, these studies do not entirely obviate the need to control for differences between university students and non-students that predate university attendance and might account for income differentials and even non-monetary outcomes.

Examination of the structure of psychopathology using latent class analysis

Several recent studies using factor analytic methods find that the structure of psychopathology reflects broad internalizing and externalizing dimensions, with the internalizing dimension being further divided into fear and distress disorders. Although these variable-centered studies have provided important insights into the structure of psychopathology, they provide limited information about the classification of individual cases. The present study examines patterns of lifetime internalizing and externalizing psychopathology in participants from the Oregon Adolescent Depression Project using latent class analysis that classifies individuals rather than variables. A 4-class solution best fits the data. The largest class (62.5%) included individuals with relatively little psychopathology; 1 class (16.4%) was largely characterized by internalizing disorders, 1 class (16.9%), largely characterized by externalizing disorders; and the final class (4.2%), characterized by both internalizing and externalizing disorders. The validity of the classes was further examined using data on psychiatric morbidity, temperament, and family aggregation of psychopathology. Classes differed on indices of positive, negative, and disinhibited temperament in ways that were consistent with theoretical predictions. Patterns of familial aggregation of psychopathology demonstrated relative specificity of transmission of different disorders. Overall, the findings support conclusions from studies of dimensional models of internalizing and externalizing disorders, and extend them to person-centered approaches to classification.

An examination of pathways from childhood maltreatment to adolescent binge drinking

Considerable clinical and empirical evidence has accumulated over the past decades indicating that there is a strong association between childhood maltreatment and heavy episodic drinking in adolescence, but there is a paucity of empirically based knowledge about the processes linking the association. The aim of this paper is to examine mechanisms that might account for the association between childhood maltreatment and heavy episodic drinking in adolescence. Using a nationally representative sample of adolescents (ages ranging 12-21; N = 6,337), this study examined the role of individual self-regulatory processes in the associations, controlling for age, gender, race/ethnicity, peer substance use, parental alcoholism, and parent-child conflict. Factor analyses were used to test the measurement structure of self-regulatory processes. Findings confirmed the association between childhood maltreatment and heavy episodic drinking in adolescence. Structural modeling analyses indicated indirect effects for childhood maltreatment primarily through poor self-regulatory processes and peer substance use. Implications for future research are discussed.

Adolescent substance use groups: antecedent and concurrent personality differences in a longitudinal study

This study attempted to extend Shedler and Block's (1990) influential study, which found that adolescent drug experimenters had the healthiest personality functioning compared to abstainers and frequent users. Using a prospective design, we examined the relationship between antecedent and concurrent personality and age-18 substance use in a community sample of 1,298 twins (96% Caucasian, 49% male). Personality measures at ages 11 and 18 assessed positive emotionality (agentic and communal), negative emotionality, and constraint. Substance use groups-abstainers, experimenters, and problem users-were created at age 18. Age-18 substance use groups differed in age-11 and age-18 constraint such that problem users were lower than experimenters, who were lower than abstainers. Age-18 substance use groups did not differ in age-18 positive emotionality. However, abstainers were significantly lower than experimenters in communal positive emotionality, whereas female abstainers scored higher in agentic positive emotionality than female experimenters, who scored higher than female problem users. Experimenters were significantly lower in negative emotionality than problem users. Our findings are inconsistent with the notion that experimenters had the healthiest personality functioning and instead suggest different strengths and weaknesses for each group. Future studies should examine agentic and communal positive emotionality separately.

Child maltreatment increases sensitivity to adverse social contexts: neighborhood physical disorder and incident binge drinking in Detroit

INTRODUCTION

Exposure to child maltreatment is associated with elevated risk for behavioral disorders in adulthood. One explanation for this life-course association is that child maltreatment increases vulnerability to the effects of subsequent stressors; however, the extent to which maltreatment increases sensitivity to social context has never been examined. We evaluated whether the association between neighborhood physical disorder and binge drinking was modified by child maltreatment exposure.

METHODS

Data were drawn from the Detroit Neighborhood Health Study, a prospective representative sample of predominately African Americans in the Detroit population. Neighborhood physical disorder was measured via systematic neighborhood assessment. Child maltreatment indicators included self-reported physical, sexual, and emotional abuse. Incident binge drinking was defined as at least one episode of ≥5 drinks (men) or ≥4 drinks (women) in the past 30-day period among those with no binge drinking at baseline (N=1013).

RESULTS

Child maltreatment and neighborhood physical disorder interacted to predict incident binge drinking (B=0.16, p=0.02) and maximum number of past 30-day drinks (B=0.15, p=0.04), such that neighborhood physical disorder predicted problematic alcohol use only among individuals with high exposure to child maltreatment.

CONCLUSION

The results add to the growing literature that African Americans in the US are exposed to an array of stressors that have pernicious consequences for problematic alcohol use. Our results document the need for increased attention to the potential for at-risk alcohol use among populations with a high degree of stress exposure.

Cognitive control links alcohol use, trait disinhibition, and reduced cognitive capacity: Evidence for medial prefrontal cortex dysregulation during reward-seeking behavior

BACKGROUND

Guided by the prediction of response-outcome theory of cognitive control (Alexander and Brown, 2010a), the present study examined reward-seeking medial prefrontal cortex (mPFC) activity as a common neuro-functional marker of excessive alcohol consumption, trait disinhibition, and reduced cognitive capacity; all of which have shown consistent patterns of covariation in previous psychometric research (e.g., Bogg and Finn, 2010).

METHODS

A sample of 18-23-year-old university students with a heterogeneous prevalence of alcohol dependence was assessed with functional magnetic resonance imaging (fMRI) while completing a version of the Balloon Analogue Risk Task (Lejuez et al., 2002). A follow-back typical weekly alcohol consumption interview, self-report measures of trait disinhibition and IQ, and a complex span working memory task also were administered.

RESULTS

Correlational region-of-interest analyses showed greater typical weekly alcohol consumption, greater trait disinhibition, and lower IQ were associated with greater reductions in mPFC activity during reward-seeking behaviors (successive inflation choices). The results also showed greater typical weekly alcohol consumption, greater trait disinhibition, and lower IQ were associated with greater increases in mPFC activity during reward-seeking outcomes (successive successful inflation outcomes). No significant relations with the measure of working memory were found.

CONCLUSIONS

The findings suggest mPFC activity during risk/reward appraisal and performance monitoring is a common neuro-functional feature of co-varying expressions of excessive alcohol consumption, trait disinhibition, and lower IQ.

Are the symptoms of cannabis use disorder best accounted for by dimensional, categorical, or factor mixture models? A comparison of male and female young adults

Despite the consensus that criteria for cannabis abuse and dependence and symptoms of withdrawal are best explained by a single latent liability, it remains unknown whether alternative models provide a better explanation of these criteria. A series of latent factor, latent class, and hybrid factor mixture models were fitted to data from 872 recent cannabis users from the Minnesota Twin Family Study who completed Diagnostic and Statistical Manual of Mental Disorders (3rd ed., revised, and 4th ed.) diagnostic criteria for cannabis abuse, dependence, and symptoms of withdrawal. Despite theoretical appeal, results did not support latent class or factor mixture modeling. Instead, symptoms of abuse, dependence, and withdrawal were better summarized by a single latent factor Cannabis Use Disorder (CUD) for male and female young adults. An almost 2-fold sex difference in item endorsement was best explained by a single mean difference on the CUD factor, indicating that young men have a greater latent liability toward expressing CUD.

Relationship between personality change and the onset and course of alcohol dependence in young adulthood

AIMS

To examine the reciprocal effects between the onset and course of alcohol use disorder (AUD) and normative changes in personality traits of behavioral disinhibition and negative emotionality during the transition between adolescence and young adulthood.

DESIGN

Longitudinal-epidemiological study assessing AUD and personality at ages 17 and 24 years.

SETTING

Participants were recruited from the community and took part in a day-long, in-person assessment.

PARTICIPANTS

Male (n = 1161) and female (n = 1022) twins participating in the Minnesota Twin Family Study.

MEASUREMENTS

The effects of onset (adolescent versus young adult) and course (persistent versus desistent) of AUD on change in personality traits of behavioral disinhibition and negative emotionality from ages 17 to 24 years.

FINDINGS

Onset and course of AUD moderated personality change from ages 17 to 24 years. Adolescent onset AUD was associated with greater decreases in behavioral disinhibition. Those with an adolescent onset and persistent course failed to exhibit normative declines in negative emotionality. Desistence was associated with a 'recovery' towards psychological maturity in young adulthood, while persistence was associated with continued personality dysfunction. Personality traits at age 11 predicted onset and course of AUD, indicating personality differences were not due to active substance abuse.

CONCLUSIONS

Personality differences present prior to initiation of alcohol use increase risk for alcohol use disorder, but the course of alcohol use disorder affects the rate of personality change during emerging adulthood. Examining the reciprocal effects of personality and alcohol use disorder within a developmental context is necessary to improve understanding for theory and intervention.

Minnesota Center for Twin and Family Research

The Minnesota Center for Twin and Family Research (MCTFR) houses a collection of longitudinal, community-based twin-family and adoptee-family projects that focus on the mental health outcomes of adolescent youth with a special focus on the development of substance use and related behavior disorders. The Minnesota Twin Family Study includes epidemiological investigations of 11- and 17-year-old twins, an examination of 11-year-old twins selected for being at high risk for having a childhood disruptive behavior disorder, and a supplemental registry of young adult twins age 18 years and older who are not enrolled in these longitudinal studies. Also, part of the MCTFR is the Sibling Interaction and Behavior Study, a complementary prospective investigation of adolescent sibling pairs in families with adoptive and biological offspring. MCTFR participants from these various projects are assessed in person and through multiple informants to provide comprehensive coverage of psychological adjustment, mental health, and psychosocial risk/protective factors. Measurement of EEG and autonomic nervous system reactivity is also part of the assessment battery for twin families. This article provides an overview of study design and includes a review of recent MCTFR findings.

Early Onset Problem Behavior, Young Adult Psychopathology, and Contextual Risk

A prospective study of 692 male twins was undertaken to investigate the relationships among early adolescent problem behavior, contextual risk, and disinhibitory psychopathology. Early adolescent problem behavior was assessed by the number of the following behaviors engaged in by the time of the age-14 assessment: (1) tobacco use, (2) alcohol use, (3) marijuana use, (4) other illicit drug use, (5) sexual intercourse, and (6) police contact. Contextual risk was assessed as a composite of measures of peer models, parent-offspring conflict, and academic engagement from the age-14 assessment. Disinhibitory psychopathology was assessed by symptoms of nicotine dependence, alcohol dependence, drug dependence, and adult antisocial behavior at the age-18 assessment. Early adolescent problem behavior and contextual risk were strongly correlated (r = .53) and both were strongly and independently associated with symptoms of disinhibitory psychopathology (r from .35 to .60). The association of early adolescent problem behavior with both contextual risk and disinhibitory psychopathology was mediated entirely by genetic factors while the association between contextual risk and disinhibitory psychopathology was mediated by both genetic and nonshared environmental factors. The results are discussed in the context of emerging research on the prognostic significance of early adolescent problem behavior for risk of adult psychopathology.

Genetic and environmental contributions to the association between anthropometric measures and iq: a study of Minnesota twins at age 11 and 17

Associations of height and head circumference with IQ are well documented, but much less is known about the association of IQ with other anthropometric measures or the mechanisms behind these associations. We therefore analyzed the associations between IQ and several anthropometric measures using a twin-study design. Twins born in Minnesota were assessed at either age 11 (756 complete pairs) or 17 (626 complete pairs) and analyzed using genetic modeling. Head circumference and height showed the most consistent positive associations with IQ, whereas more detailed anthropometric measures were not significantly better predictors of IQ. These associations were mainly due to common genetic factors. Our results suggest that the same genetic factors have an effect on physical and cognitive development. Head circumference and height capture information on children's physical development, which is partly associated also with cognitive development.

Strategies for characterizing complex phenotypes and environments: general and specific family environmental predictors of young adult tobacco dependence, alcohol use disorder, and co-occurring problems

BACKGROUND

Defining phenotypes in studies of tobacco and alcohol misuse is difficult because of the complexity of these behaviors and their strong association with each other and with other problem behaviors. The present paper suggests a strategy for addressing this issue by conceptualizing and partitioning variance in phenotypes into either general or substance/behavior-specific. The paper also applies the general or substance/behavior-specific conceptualization to environmental predictors of tobacco and alcohol misuse and other problem behaviors.

METHODS

Data were drawn from the Seattle Social Development Project, a contemporary, ethnically diverse and gender-balanced longitudinal panel including 808 participants. Latent variable modeling was used to partition variance in young adult (age 24) nicotine dependence, alcohol abuse and dependence, illicit drug abuse and dependence, involvement in crime, and engagement in HIV sexual risk behavior into general problem behavior and behavior-specific variance. Similarly, measures of general, drinking-specific, and smoking-specific adolescent family environment were constructed.

RESULTS

Consistent with expectations, more positive general family environment during adolescence was associated with lower levels of shared variance in problem behaviors at age 24, but not with unique variance in tobacco or alcohol use disorder. Higher levels of family smoking and drinking environments during adolescence, however, were positively associated with unique variance in tobacco and alcohol use disorder, respectively, but did not predict shared variance in problem behaviors.

CONCLUSIONS

Results support the utility of the proposed approach. Ways in which this approach might contribute to future molecular genetic studies are discussed.

Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies

A meta-analysis of twin, family and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on impulsivity. The best fitting model for 41 key studies (58 independent samples from 14 month old infants to adults; N=27,147) included equal proportions of variance due to genetic (0.50) and non-shared environmental (0.50) influences, with genetic effects being both additive (0.38) and non-additive (0.12). Shared environmental effects were unimportant in explaining individual differences in impulsivity. Age, sex, and study design (twin vs. adoption) were all significant moderators of the magnitude of genetic and environmental influences on impulsivity. The relative contribution of genetic effects (broad sense heritability) and unique environmental effects were also found to be important throughout development from childhood to adulthood. Total genetic effects were found to be important for all ages, but appeared to be strongest in children. Analyses also demonstrated that genetic effects appeared to be stronger in males than in females. Method of assessment (laboratory tasks vs. questionnaires), however, was not a significant moderator of the genetic and environmental influences on impulsivity. These results provide a structured synthesis of existing behavior genetic studies on impulsivity by providing a clearer understanding of the relative genetic and environmental contributions in impulsive traits through various stages of development.

Components of Disinhibition (Vs. Constraint) Differentially Predict Aggression and Alcohol Use

Disinhibition (vs. Constraint; DvC), which has been shown to represent a central aspect of the externalizing domain, consists of several correlated but distinguishable underlying traits, which may have different patterns of association with various externalizing indicators. In a sample of 18– to 19–year old undergraduate students ( N = 430; 71.1% female), we examined the specificity and generality of the association between lower order components of DvC and both aggression and alcohol use, externalizing–related behavioural constructs that have well–established links to DvC. All three components of DvC—including Disagreeableness, low Self–Control and low Accomplishment—were associated independently with Reactive Aggression, but only Disagreeableness was correlated significantly with Proactive Aggression. Also, only low Self–Control was associated with alcohol use. Thus, aggression was broadly associated with components of DvC—although much more strongly with the Disagreeableness domain—whereas alcohol use was specifically correlated with low Self–Control. These results suggest that lower order components of DvC have distinct patterns of associations with externalizing–related outcomes. Copyright © 2011 John Wiley & Sons, Ltd.

The social norms of birth cohorts and adolescent marijuana use in the United States, 1976-2007

AIMS

Studies of the relationship between social norms and marijuana use have generally focused on individual attitudes, leaving the influence of larger societal-level attitudes unknown. The present study investigated societal-level disapproval of marijuana use defined by birth cohort or by time-period.

DESIGN

Combined analysis of nationally representative annual surveys of secondary school students in the United States conducted from 1976 to 2007 as part of the Monitoring the Future study.

SETTING

In-school surveys completed by adolescents in the United States.

PARTICIPANTS

A total of 986 003 adolescents in grades 8, 10 and 12.

MEASUREMENTS

Main predictors included the percentage of students who disapproved of marijuana in each birth cohort and time-period. Multi-level models with individuals clustered in time-periods of observation and birth cohorts were modeled, with past-year marijuana use as the outcome.

FINDINGS

Results indicated a significant and strong effect of birth cohort disapproval of marijuana use in predicting individual risk of marijuana use, after controlling for individual-level disapproval, perceived norms towards marijuana and other characteristics. Compared to birth cohorts in which most (87-90.9%) adolescents disapproved of marijuana use, odds of marijuana use were 3.53 times higher in cohorts where fewer than half (42-46.9%) disapproved (99% confidence interval: 2.75, 4.53).

CONCLUSIONS

Individuals in birth cohorts that are more disapproving of marijuana use are less likely to use, independent of their personal attitudes towards marijuana use. Social norms and attitudes regarding marijuana use cluster in birth cohorts, and this clustering has a direct effect on marijuana use even after controlling for individual attitudes and perceptions of norms.

Understanding general and specific connections between psychopathology and marital distress: a model based approach

Marital distress is linked to many types of mental disorders; however, no study to date has examined this link in the context of empirically based hierarchical models of psychopathology. There may be general associations between low levels of marital quality and broad groups of comorbid psychiatric disorders as well as links between marital adjustment and specific types of mental disorders. The authors examined this issue in a sample (N = 929 couples) of currently married couples from the Minnesota Twin Family Study who completed self-report measures of relationship adjustment and were also assessed for common mental disorders. Structural equation modeling indicated that (a) higher standing on latent factors of internalizing (INT) and externalizing (EXT) psychopathology was associated with lower standing on latent factors of general marital adjustment for both husbands and wives, (b) the magnitude of these effects was similar across husbands and wives, and (c) there were no residual associations between any specific mental disorder and overall relationship adjustment after controlling for the INT and EXT factors. These findings point to the utility of hierarchical models in understanding psychopathology and its correlates. Much of the link between mental disorder and marital distress operated at the level of broad spectrums of psychopathological variation (i.e., higher levels of marital distress were associated with disorder comorbidity), suggesting that the temperamental core of these spectrums contributes not only to symptoms of mental illness but to the behaviors that lead to impaired marital quality in adulthood.

Fluid intelligence and psychosocial outcome: from logical problem solving to social adaptation

Background

While fluid intelligence has proved to be central to executive functioning, logical reasoning and other frontal functions, the role of this ability in psychosocial adaptation has not been well characterized.

Methodology/Principal Findings

A random-probabilistic sample of 2370 secondary school students completed measures of fluid intelligence (Raven's Progressive Matrices, RPM) and several measures of psychological adaptation: bullying (Delaware Bullying Questionnaire), domestic abuse of adolescents (Conflict Tactic Scale), drug intake (ONUDD), self-esteem (Rosenberg's Self Esteem Scale) and the Perceived Mental Health Scale (Spanish adaptation).

Lower fluid intelligence scores were associated with physical violence, both in the role of victim and victimizer. Drug intake, especially cannabis, cocaine and inhalants and lower self-esteem were also associated with lower fluid intelligence. Finally, scores on the perceived mental health assessment were better when fluid intelligence scores were higher.

Conclusions/Significance

Our results show evidence of a strong association between psychosocial adaptation and fluid intelligence, suggesting that the latter is not only central to executive functioning but also forms part of a more general capacity for adaptation to social contexts.

Externalizing psychopathology and behavioral disinhibition: working memory mediates signal discriminability and reinforcement moderates response bias in approach-avoidance learning

Research has suggested that reduced working memory capacity plays a key role in disinhibited patterns of behavior associated with externalizing psychopathology. In this study, participants (N = 365) completed 2 versions of a go/no-go mixed-incentive learning task that differed in the relative frequency of monetary rewards and punishments for correct and incorrect active-approach responses, respectively. Using separate structural equation models for conventional (hit and false alarm rates) and signal detection theory (signal discriminability and response bias) performance indices, distinct roles for working memory capacity and changes in payoff structure were found. Specifically, results showed that (a) working memory capacity mediated the effects of externalizing psychopathology on false alarms and discriminability of go versus no-go signals; (b) these effects were not moderated by the relative frequency of monetary rewards and punishments; (c) the relative frequency of monetary rewards and punishments moderated the effects of externalizing psychopathology on hits and response bias for go versus no-go responses; and (d) these effects were not mediated by working memory capacity. The findings implicate distinct roles for reduced working memory capacity and poorly modulated active approach and passive avoidance in the link between externalizing psychopathology and behavioral disinhibition.

A Twin and Adoption Study of Reading Achievement: Exploration of Shared-Environmental and Gene-Environment-Interaction Effects

Existing behavior-genetic research implicates substantial influence of heredity and modest influence of shared environment on reading achievement and reading disability. Applying DeFries-Fulker analysis to a combined sample of twins and adoptees (N = 4,886, including 266 reading-disabled probands), the present study replicates prior findings of considerable heritability for both reading achievement and reading disability. A simple biometric model adequately described parent and offspring data (combined N = 9,430 parents and offspring) across differing types of families present in the sample Analyses yielded a high heritability estimate (around 0.70) and a negligible shared-environmentality estimate for both reading achievement and reading disability. No evidence of gene × environment interaction was found for parental reading ability and parental educational attainment, the two moderators analyzed.

Genome-wide association study of conduct disorder symptomatology

Conduct disorder (CD) is one of the most prevalent childhood psychiatric conditions, and is associated with a number of serious concomitant and future problems. CD symptomatology is known to have a considerable genetic component, with heritability estimates in the range of 50%. Despite this, there is a relative paucity of studies aimed at identifying genes involved in the susceptibility to CD. In this study, we report results from a genome-wide association study of CD symptoms. CD symptoms were retrospectively reported by a psychiatric interview among a sample of cases and controls, in which cases met the criteria for alcohol dependence. Our primary phenotype was the natural log transformation of the number of CD symptoms that were endorsed, with data available for 3963 individuals who were genotyped on the Illumina Human 1M beadchip array. Secondary analyses are presented for case versus control status, in which caseness was established as endorsing three or more CD symptoms (N = 872 with CD and N = 3091 without CD). We find four markers that meet the criteria for genome-wide significance (P<5 × 10(-8)) with the CD symptom count, two of which are located in the gene C1QTNF7 (C1q and tumor necrosis factor-related protein 7). There were six additional SNPs in the gene that yielded converging evidence of association. These data provide the first evidence of a specific gene that is associated with CD symptomatology. None of the top signals resided in traditional candidate genes, underscoring the importance of a genome-wide approach for identifying novel variants involved in this serious childhood disorder.

Genetic and environmental influences on personality trait stability and growth during the transition to adulthood: a three-wave longitudinal study

During the transition to adulthood individuals typically settle into adult roles in love and work. This transition also involves significant changes in personality traits that are generally in the direction of greater maturity and increased stability. Competing hypotheses have been offered to account for these personality changes: The intrinsic maturation hypothesis suggests that change trajectories are endogenous, whereas the life-course hypothesis suggests that these changes occur because of transactions with the social environment. This study investigated the patterns and origins of personality trait changes from ages 17 to 29 using 3 waves of Multidimensional Personality Questionnaire data provided by twins. Results suggest that (a) trait changes were more profound in the first relative to the second half of the transition to adulthood; (b) traits tend to become more stable during the second half of this transition, with all the traits yielding retest correlations between .74 and .78; (c) Negative Affectivity declined over time, and Constraint increased over time; minimal change was observed on agentic or communal aspects of Positive Emotionality; and (d) both genetic and nonshared environmental factors accounted for personality changes. Overall, these genetically informed results support a life-course perspective on personality development during the transition to adulthood.

Explaining associations between cannabis use disorders in adolescence and later major depression: a test of the psychosocial failure model

AIMS

Cannabis use disorders (CUDs) in adolescence are associated with increased risk for later major depressive disorder (MDD). The goal of this study was to examine the "psychosocial failure" explanation for this association: the possibility that psychosocial consequences of CUDs in adolescence account for the increased risk for later MDD.

METHODS

Participants (n=1252) were drawn from the community-based sample of the Minnesota Twin Family Study and were assessed at ages 17, 20, and 24. CUDs and MDD were assessed via structured interview. "Psychosocial failure" was defined as educational failure (high school dropout), occupational failure (persistent unemployment), or engagement in crime.

RESULTS

Psychosocial failure partially mediated the association between CUDs in adolescence and later MDD.

CONCLUSIONS

The adverse psychosocial consequences of CUDs in adolescence partially - but not fully - account for the observed association between early CUDs and later MDD.

Age-of-onset or behavioral sub-types? A prospective comparison of two approaches to characterizing the heterogeneity within antisocial behavior

There are two common approaches to sub-typing the well-documented heterogeneity within antisocial behavior: age-of-onset (i.e., childhood-onset versus adolescence-onset; see Moffitt 1993) and behavioral (i.e., physical aggression versus non-aggressive rule-breaking). These approaches appear to be associated, such that aggression is more characteristic of childhood-onset antisocial behavior whereas rule-breaking is linked to both child- and adolescence-onset antisocial behavior. However, it remains unclear which approach, if either, better explains the heterogeneity within antisocial behavior. We examined this question in a prospective sample of male twins, assessed at the ages of 11, 14, 17, and 24 years. Although the age-of-onset subtypes predicted adult antisocial behavior in the expected direction when analyzed alone, this association dissipated once we controlled for aggression and rule-breaking. Such findings suggest that the behavioral sub-types of antisocial behavior may be a stronger predictor of later antisocial outcomes than is its age-of-onset.

Testing the role of adolescent sexual initiation in later-life sexual risk behavior: a longitudinal twin design

The consistent association between adolescent sexual initiation (ASI) and risky adult sexual behavior (RASB) has generally been assumed to indicate that ASI has a causal effect on RASB; consequently, it is assumed that delaying ASI will reduce RASB. Yet the ASI-RASB association might be better accounted for by some third variable. We evaluated the causal role of ASI (initiation of oral, anal, or vaginal sex at or before age 16) in influencing RASB in a longitudinal sample of 2,173 twins (followed from ages 11 to 24 or from ages 17 to 29) using two methods: the discordant-twin design and the propensity-score design. The former controlled for unmeasured genetic and shared environmental factors, and the latter controlled for measured nonshared environmental factors. We replicated the link between ASI and RASB reported in previous research, but results from the discordant-twin and propensity-score analyses suggested that this association is better explained by common genetic or environmental risk factors than as a causal effect. These findings suggest that preventing ASI is unlikely to reduce RASB.

New variable selection methods for zero-inflated count data with applications to the substance abuse field

Zero-inflated count data are very common in health surveys. This study develops new variable selection methods for the zero-inflated Poisson regression model. Our simulations demonstrate the negative consequences which arise from the ignorance of zero-inflation. Among the competing methods, the one-step SCAD method is recommended because it has the highest specificity, sensitivity, exact fit, and lowest estimation error. The design of the simulations is based on the special features of two large national databases commonly used in the alcoholism and substance abuse field so that our findings can be easily generalized to the real settings. Applications of the methodology are demonstrated by empirical analyses on the data from a well-known alcohol study.