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Both genes and the environment are important for individual differences in expertise, but little is known about gene--environment interactions underlying domain-specific achievement. Here we explored this issue in a large Swedish twin cohort (N = 6,610), using moderator modeling with musical expertise as a model domain. Specifically, we tested whether musical enrichment of the childhood environment moderates adult musical achievement, as well as the magnitude of genetic and nongenetic influences on individual differences in achievement. Musical achievement was measured using the Creative Achieve- ment Questionnaire and enrichment of the childhood environment was indexed with a principal com- ponent derived from the number of music records in the family home, number of individuals in the family environment playing an instrument, frequency of concert visits, and music education before the age of 12. As expected, we found a positive association between childhood musical enrichment and musical achievement in adulthood. Interestingly, however, the total variance in musical achievement as well as the relative importance of genetic influences increased with a higher level of musical enrichment. Estimates of genetic and environmental influences as well as the magnitude of the environmental moderation differed for men and women. These findings suggest that, in line with recent multifactorial models of expert performance, a musically enriched childhood environment amplifies individual differ- ences, an effect which is largely driven by an increase in the importance of genetic factors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: We validated the Social Mistrust Scale (SMS) and utilized it to examine the structure, prevalence, and heritability of social mistrust in a large sample of Chinese children and adolescents.Methods: In Study 1, a large sample of healthy twins (N=2094) aged 8 to 14years (M=10.27years, SD=2) completed the SMS. Structural equation modeling (SEM) was conducted to assess the structure of the SMS and to estimate the heritability of social mistrust in a sub-sample of twins (n=756 pairs). In Study 2, 32 adolescents with childhood-onset schizophrenia were compared with 34 healthy controls on levels of suspiciousness and clinical symptoms to examine the associations between the SMS and the Positive and Negative Syndrome Scale (PANSS).Results: We found a three-factor structure for social mistrust (home, school, and general mistrust). Social mistrust was found to be moderately - heritable (19%-40%), with mistrust at home most strongly influenced by genetic factors. Compared with 11.76% of the healthy controls, 56.25% of the adolescents with early-onset schizophrenia exhibited very high levels of social mistrust on all three subscales of the SMS. The SMS exhibited good discriminant validity in distinguishing adolescents with childhood-onset schizophrenia from healthy controls and showed associations with a broad range of symptoms assessed by the PANSS.Conclusions: Social mistrust assessed by the SMS may be heritable. The SMS demonstrates good discriminant validity with clinical diagnoses of schizophrenia. However, it seems to be correlated with multiple aspects of psychopathology in the schizophrenia group, rather than being specific to delusional ideation/paranoia. [ABSTRACT FROM AUTHOR]

Twin registers are wonderful research resources for research applications in medical and behavioral genetics, epidemiology, psychology, molecular genetics, and other areas of research. New registers continue to be launched all over the world as researchers from different disciplines recognize the potential to boost and widen their research agenda. In this article, we discuss multiple aspects that need to be taken into account when initiating a register, from its preliminary sketch to its actual development. This encompasses aspects related to the strategic planning and key elements of research designs, promotion and management of a twin register, including recruitment and retaining of twins and family members of twins, phenotyping, database organization, and collaborations between registers. We also present information on questions unique to twin registers and twin-biobanks, such as the assessment of zygosity by SNP arrays, the design of (biomarker) studies involving related participants, and the analyses of clustered data. Altogether, we provide a number of basic guidelines and recommendations for reflection when planning a twin register. [ABSTRACT FROM AUTHOR]

Most studies of life experiences rely on retrospective self-reports due to the major advantages of this method of data collection. However, some clinicians and researchers express doubts regarding the reliability of self-reports about lived experiences. One option to explore reliability is to assess two or more sources of information, a procedure usually labeled agreement, which consists of the comparison of a self-report (main participant) and a collateral report, to assess whether both reporters describe the same experiences (concordance) and/or to explore whether the collateral confirms the experiences reported by the main participant (corroboration). We studied concordance and corroboration of positive and negative life experiences in 47 pairs of adult twins (N = 94), both genders, 18-50 years of age; 32 pairs were monozygotic. Participants were asked about their own life experiences (to assess concordance) and about their twin’s life experiences (to assess corroboration). Overall agreement between twins was quite acceptable, although it was heterogeneous across items and/or domains. For instance, physical abuse presented a moderate kappa for concordance, while sexual abuse achieved a poor kappa. Corroboration presented globally higher kappa than concordance, suggesting that twins seem to be especially good source of collateral information. Remarkably, when valence (i.e., positive vs. negative experiences) was analyzed, concordance and corroboration were higher for positives experiences than for negative ones. Our results suggest that self- and collateral-reports are reliable means of assessing life experiences, which has important implications for future research. [ABSTRACT FROM AUTHOR]

Introduction: Genetic factors contribute to individual differences in physical activity, but it remains uncertain whether the magnitude of the genetic effects is modified by variations in home environments. We aimed to examine to what extent the psychosocial home environment in childhood and adolescence modifies the genetic influences on leisure time physical activity in young adulthood. Methods: Participants were Finnish twins (N = 3305) who reported their leisure time physical activity at age 24 yr. The psychosocial home environment was assessed by twins at ages 12, 14, and 17 yr, as well as by their parents when the twins were age 12 yr. Gene-environment interaction modeling was performed with OpenMx software. Results: Parental ratings of positive home atmosphere as well as the twins' ratings of both positive home atmosphere at age 14 yr and lower relational tensions at ages 12 and 14 yr predicted higher leisure time physical activity levels in young adulthood (regression coefficients = 0.33-0.64). Parental perceptions as well as the twins' perceptions of positive home atmosphere at ages 14 and 17 yr increased the additive genetic variation (moderation effects: 0.55, 95% confidence interval [CI] = 0.29-0.80; 0.60, 95% CI = 0.26-1.05; and 0.52, 95% CI = 0.19-0.87, respectively). The twins' ratings of positive home atmosphere at age 12 yr and lower relational tensions at ages 12 and 14 yr increased the unique environmental variation of their subsequent physical activity (moderation effects: 0.46, 95% CI = 0.19-0.60; 0.48, 95% CI = 0.29-0.64; and 0.85, 95% CI = 0.12-0.95, respectively). Conclusions: A psychosocial home environment that is warm and supportive in childhood and adolescence not only increases the mean level of subsequent leisure time physical activity in young adulthood but also modifies the genetic and environmental variances in leisure time physical activity. [ABSTRACT FROM AUTHOR]

Objective: This study examined the effects of childhood attention deficit hyperactivity disorder (ADHD) symptoms, both inattention and hyperactivity-impulsivity, on the development of smoking in male and female adolescents.Method: Twin difference methods were used to control for shared genetic and environmental confounders in three population-based, same-sex twin samples (N=3,762; 64% monozygotic). One cohort oversampled female adolescents with ADHD beginning in childhood. Regressions of childhood inattentive and hyperactive-impulsive symptoms were conducted to predict smoking outcomes by age 17. ADHD effects were divided into those shared between twins in the pair and those nonshared, or different within pairs.Results: Adolescents who had more severe ADHD symptoms as children were more likely to initiate smoking and to start smoking younger. The association of ADHD symptoms with daily smoking, number of cigarettes per day, and nicotine dependence was greater in females than in males. Monozygotic female twins with greater attentional problems than their co-twins had greater nicotine involvement, consistent with possible causal influence. These effects remained when co-occurring externalizing behaviors and stimulant medication were considered. Hyperactivity-impulsivity, while also more strongly related to smoking for female adolescents, appeared primarily noncausal.Conclusions: Smoking initiation and escalation are affected differentially by ADHD subtype and gender. The association of inattention with smoking in female adolescents may be causal, whereas hyperactivity-impulsivity appears to act indirectly, through shared propensities for both ADHD and smoking. [ABSTRACT FROM AUTHOR]

Importance: Exposure to bullying is associated with poor mental health. However, the degree to which observed associations reflect direct detrimental contributions of exposure to bullying to mental health remains uncertain, as noncausal relationships may arise from genetic and environmental confounding (eg, preexisting vulnerabilities). Determining to what extent exposure to bullying contributes to mental health is an important concern, with implications for primary and secondary interventions.Objective: To characterize the concurrent and longitudinal contribution of exposure to bullying to mental health in childhood and adolescence using a twin differences design to strengthen causal inference.Design, Setting, and Participants: Participants were drawn from the Twins Early Development Study, a population-based cohort recruited from population records of births in England and Wales between January 1, 1994, and December 31, 1996. Data collection took place when the participants were between 11 and 16 years of age from December 1, 2005, to January 31, 2013. Data analysis was conducted from January 1, 2016, to June 20, 2017.Exposures: Participants completed the Multidimensional Peer-Victimization Scale at 11 and 14 years of age.Main Outcomes and Measures: Mental health assessments at 11 and 16 years of age included anxiety, depression, hyperactivity and impulsivity, inattention, conduct problems, and psychotic-like experiences (eg, paranoid thoughts or cognitive disorganization).Results: The 11 108 twins included in the final sample (5894 girls and 5214 boys) were a mean age of 11.3 years at the first assessment and 16.3 years at the last assessment. The most stringent twin differences estimates (monozygotic) were consistent with causal contribution of exposure to bullying at 11 years to concurrent anxiety, depression, hyperactivity and impulsivity, inattention, and conduct problems. Effects decreased over time; that is, substantial concurrent contributions to anxiety (β = 0.27; 95% CI, 0.22-0.33) persisted for 2 years (β = 0.12; 95% CI, 0.04-0.20) but not 5 years. Direct contributions to paranoid thoughts and cognitive disorganization persisted for 5 years.Conclusions and Relevance: This study is the largest to date to characterize the contribution of exposure to bullying in childhood to mental health using a twin differences design and multi-informant, multiscale data. Stringent evidence of the direct detrimental contribution of exposure to bullying in childhood to mental health is provided. Findings also suggest that childhood exposure to bullying may partly be viewed as a symptom of preexisting vulnerabilities. Finally, the dissipation of effects over time for many outcomes highlights the potential for resilience in children who were bullied. In addition to programs that aim to reduce exposure to bullying, interventions may benefit from addressing preexisting vulnerabilities and focus on resilience. [ABSTRACT FROM AUTHOR]

The goal of this study was to investigate parental involvement as an etiologic moderator of oppositional defiant disorder (ODD) during middle childhood. Previous studies examining the influence of genetic and environmental factors on ODD have not considered whether and how these factors might vary by parental involvement. We thus conducted a series of "latent genetic by measured environmental" interaction analyses, in which measured parental involvement was allowed to moderate genetic, shared, and nonshared environmental influences on child ODD. Participants include 1,027 twin pairs (age ranged from 6 to 11 years old) from the Michigan State University Twin Registry. Results did indeed suggest that the etiology of ODD varies with maternal involvement, such that genetic influence on ODD became more prominent as maternal involvement decreased. However, these results were specific to children's perceptions of maternal involvement and did not extend to maternal perceptions of her involvement. There was no evidence that paternal involvement moderated the etiology of ODD, regardless of informant. The different results found in twins' and parents' data are consistent with those in previous research showing that children may have different perceptions from parents' about their family relationships and that this discrepancy needs to be taken into account in future research. (PsycINFO Database Record [ABSTRACT FROM AUTHOR]

Background: Shared experiences within families play an important role in the initiation of cigarette use among adolescents. Behavioral genetic studies using various samples have implicated that the shared environment that twins experience is an important source of influence on whether adolescents initiate cigarette use. Whether the special twin environment, in addition to the shared environment, contributes significantly to making twin siblings more similar in cigarette initiation, and whether the influence of the special twin environment persists into adulthood, is less clear.Methods: Data for this study came from the National Longitudinal Survey of Adolescent Health. Twin, full-, and half-sibling pairs between the ages of 12 and 33 were separated into three age groups, with about 3,000 individuals in each age group. The proportion of variance in cigarette use initiation explained by genetic, shared, special twin, and unique environmental factors were examined.Results: The results of separate age-moderated univariate variance decomposition models indicate that the special twin environment does not significantly contribute to the variance in cigarette use initiation in adolescence or young adulthood.Conclusion: Factors shared by individuals in a family, but that are not specific to being a twin, are important in determining whether adolescents will initiate the use of cigarettes. [ABSTRACT FROM AUTHOR]

It has been argued that facets do not represent the bottom of the personality hierarchy—even more specific personality characteristics, nuances, could be useful for describing and understanding individuals and their differences. Combining 2 samples of German twins, we assessed the consensual validity (correlations across different observers), rank-order stability, and heritability of nuances. Personality nuances were operationalized as the 240 items of the Revised NEO Personality Inventory (NEO-PI-R). Their attributes were examined by analyzing item residuals, controlling for the variance of the facet the item had been assigned to and all other facets. Most nuances demonstrated significant {p < .0002) cross-method agreement and rank-order stability. A substantial proportion of them (48% in self-reports, 20% in informant ratings, and 50% in combined ratings) demonstrated a significant (p < .0002) component of additive genetic variance, whereas evidence for environmental influences shared by twins was modest. Applying a procedure to estimate stability and heritability of true scores of item residuals yielded estimates comparable with those of higher-order personality traits, with median estimates of rank-order stability and heritability being .77 and .52, respectively. Few nuances demonstrated robust associations with age and gender, but many showed incremental, conceptually meaningful, and replicable (across methods and/or samples) predictive validity for a range of interest domains and body mass index. We argue that these narrow personality characteristics constitute a valid level of the personality hierarchy. They may be especially useful for providing a deep and contextualized description of the individual, but also for the prediction of specific outcomes. [ABSTRACT FROM AUTHOR]

Marriage is associated with reductions in both perceived stress and depressive symptoms, two constructs found to be influenced by common genetic effects. A study of sibling twins was used to test whether marriage decreases the proportion of variance in depressive symptoms accounted for by genetic and environmental effects underlying perceived stress. The sample consisted of 1,612 male and female twin pairs from the University of Washington Twin Registry. The stress-buffering role of marriage was tested relative to two unmarried groups: the never married and the divorced. Multivariate twin models showed that marriage reduced genetic effects of perceived stress on depressive symptoms but did not reduce environmental effects. The findings suggest a potential marital trade-off for women: access to a spouse may decrease genetic effects of perceived stress on depressive symptoms, although marital and family demands may increase environmental effects of perceived stress on depressive symptoms. [ABSTRACT FROM AUTHOR]

Background: Psychiatry has long sought to develop biological diagnostic subtypes based on symptomatic differences. This effort assumes that symptoms reflect, with good fidelity, underlying etiological processes. We address this question for major depression (MD).Methods: We examine, in twins from a population-based registry, similarity in symptom endorsement in individuals meeting criteria for last-year MD at separate interview waves and in concordant twin pairs. Among individuals with MD, we explore the impact of genetic-temperamental and child adversity risk factors on individual reported symptoms. Aggregated criteria do not separate insomnia from hypersomnia, weight gain from loss, etc. while disaggregated criteria do.Results: In twins with MD at two different waves, the mean tetrachoric correlations (±SEM) for aggregated and disaggregated DSM-IV A criteria were, respectively, +0.31 ± 0.06 and +0.34 ± 0.03. In monozygotic (MZ) and dizygotic (DZ) twin pairs concordant for last-year MD, the mean tetrachoric correlations for aggregated and disaggregated criteria were, respectively, +0.33 ± 0.07 and +0.43 ± 0.04, and +0.05 ± 0.08 and +0.07 ± 0.04. In individuals meeting MD criteria, neuroticism predicted the most MD symptoms (10), followed by childhood sexual abuse (8), low parental warmth (6), and genetic risk (4).Conclusions: The correlations for individual depressive symptoms over multiple episodes and within MZ twins concordant for MD are modest suggesting the important role of transient influences. The multidetermination of individual symptoms was further evidenced by their prediction by personality and exposure to early life adversities. The multiple factors influencing symptomatic presentation in MD may contribute to our difficulties in isolating clinical depressive subtypes with distinct pathophysiologies. [ABSTRACT FROM AUTHOR]

Children and their parents often differ in their perception of the relationship they share. As this relationship changes developmentally, the nature of these differences may also change. Longitudinal genetic designs can be used to investigate the developmental etiologies of shared and distinct perceptions. In this study, we used longitudinal psychometric models to analyze child and parent reports of negative parenting for 6417 twin pairs from the Twins Early Development Study at ages 9, 12 and 14 years. Within-time cross-reporter correlations, indicating the degree to which children and parents perceived negative parenting behaviors similarly at each age, were moderate ( r = .44 − .46). Longitudinal genetic analyses revealed these shared perceptions to be relatively stable during the transition into adolescence, with this stability driven by a combination of children's genetic factors and family-wide environmental factors. In contrast, child- and parent-specific perceptions of parenting were predominantly age-specific, a developmental pattern underpinned by child genetic factors and a combination of family-wide and unique environmental influences. These results and their implications are discussed in the context of interplay between reciprocal interactions, subjective insight and developmental behavioral change in the parent-child relationship. [ABSTRACT FROM AUTHOR]

Study Question: Compared to families with IVF singletons, what are parental depressive, parent-adolescent interaction and adolescent adjustment outcomes in families with 11-17-year-old IVF twins?Summary Answer: No differences were detected for any measured outcome between families with 11-17-year-old IVF twins and those with IVF singletons, despite high statistical power.What Is Known Already: When IVF twins are younger than 5-years-old, parents tend to have more mental health difficulties and poorer parent-child interactions relative to IVF singletons. By middle childhood, these differences may no longer exist and available studies with middle childhood-aged IVF twins challenge the expected long-term implications of the early concerns. IVF twins may even have more optimum adjustment than IVF singletons in middle childhood.Study Design, Size, Duration: Study of 280, 11-17-year-old IVF children (n = 122 twins and n = 158 singletons) from 195 families at a US reproductive endocrinology clinic.Participants/materials, Setting, Method: At Wave 1, clinic patients with an IVF child born between 1998 and 2004 were invited to participate in an online survey. In this follow-up study, mothers and fathers provided information on each of their 11-17-year-old IVF adolescents.Main Results and the Role Of Chance: There were no differences between 11- and 17-year-old IVF twins and IVF singletons in parent depressive symptoms, parent-adolescent interactions or adolescent adjustment outcomes.Limitations Reasons For Caution: Although the family demographics are representative of IVF patients, participants were drawn from one US clinic.Wider Implications Of the Findings: Study results provide reassurance that by adolescence IVF twins and their families function as well as IVF singletons and their families.Study Funding/competing Interests: University of Minnesota (UMN) Agriculture Experiment Station (MN-52-107), UMN Grant-in-Aid of Research, Artistry and Scholarship, UMN College of Education and Human Development Research Development Investment Grant, UMN Women's Philosophic Leadership Circle Award, UMN Eva Miller Endowed Fellowship. The authors have no conflicts of interest to declare. [ABSTRACT FROM AUTHOR]

Environmental factors play a key role in the development of Attention-Deficit/Hyperactivity Disorder (ADHD), but the long-term effects of these factors are still unclear. This study analyses data from 1024 monozygotic (identical) twins in Australia, the United States, and Scandinavia who were assessed for ADHD in Preschool, Kindergarten, Grade 1, and Grade 2. Differences within each twin pair were used as a direct measure of non-shared environmental effects. The Trait-State-Occasion (TSO) model developed by Cole et al. (Psychological Methods, 10, 3-20, 2005) was used to separate the non-shared environmental effects into stable factors, and transient factors that excluded measurement error. Stable factors explained, on average, 44 % and 39 % of the environmental variance in hyperactive-impulsive and inattentive symptoms, respectively. Transient effects explained the remaining 56 % and 60 % of variance. The proportion of stable variance was higher than expected based on previous research, suggesting promise for targeted interventions if future research identifies these stable risk factors. [ABSTRACT FROM AUTHOR]

Mental wellbeing and mental illness symptoms are typically conceptualized as opposite ends of a continuum, despite only sharing about a quarter in common variance. We investigated the normative variation in measures of wellbeing and of depression and anxiety in 1486 twins who did not meet clinical criteria for an overt diagnosis. We quantified the shared versus distinct genetic and environmental variance between wellbeing and depression and anxiety symptoms. The majority of participants (93%) reported levels of depression and anxiety symptoms within the healthy range, yet only 23% reported a wellbeing score within the “flourishing” range: the remainder were within the ranges of “moderate” (67%) or “languishing” (10%). In twin models, measures of wellbeing and of depression and anxiety shared 50.09% of variance due to genetic factors and 18.27% due to environmental factors; the rest of the variance was due to unique variation impacting wellbeing or depression and anxiety symptoms. These findings suggest that an absence of clinically-significant symptoms of depression and anxiety does not necessarily indicate that an individual is flourishing. Both unique and shared genetic and environmental factors may determine why some individuals flourish in the absence of symptoms while others do not. [ABSTRACT FROM AUTHOR]

Research using twins has found that much of the variability in externalizing phenotypes-including alcohol and drug use, impulsive personality traits, risky sex, and property crime-is explained by genetic factors. Nevertheless, identification of specific genes and variants associated with these traits has proven to be difficult, likely because individual differences in externalizing are explained by many genes of small individual effect. Moreover, twin research indicates that heritable variance in externalizing behaviors is mostly shared across the externalizing spectrum rather than specific to any behavior. We use a longitudinal, "deep phenotyping" approach to model a general externalizing factor reflecting persistent engagement in a variety of socially problematic behaviors measured at 11 assessment occasions spanning early adulthood (ages 18 to 28). In an ancestrally homogenous sample of non-Hispanic Whites (N = 337), we then tested for enrichment of associations between the persistent externalizing factor and a set of 3,281 polymorphisms within 104 genes that were previously identified as associated with alcohol-use behaviors. Next, we tested for enrichment among domain-specific factors (e.g., property crime) composed of residual variance not accounted for by the common factor. Significance was determined relative to bootstrapped empirical thresholds derived from permutations of phenotypic data. Results indicated significant enrichment of genetic associations for persistent externalizing, but not for domain-specific factors. Consistent with twin research findings, these results suggest that genetic variants are broadly associated with externalizing behaviors rather than unique to specific behaviors. (PsycINFO Database Record [ABSTRACT FROM AUTHOR]

Background: Use of cigarettes and cannabis frequently co-occurs. We examine the role of genetic and environmental influences on variation in and covariation between tobacco cigarette and cannabis use across European-American (EA) and African-American (AA) women.Methods: Data on lifetime cannabis and cigarette use were drawn from interviews of 956 AA and 3557 EA young adult female twins and non-twin same sex female full siblings. Twin modeling was used to decompose variance in and covariance between cigarette and cannabis use into additive genetic, shared, special twin and non-shared environmental sources.Results: Cigarette use was more common in EAs (75.3%, 95% C.I. 73.8-76.7%) than AAs (64.2%, 95% C.I. 61.2-67.2%) while cannabis use was marginally more commonly reported by AAs (55.5%, 95% C.I. 52.5-58.8%) than EAs (52.4%, 95% C.I. 50.7-54.0%). Additive genetic factors were responsible for 43-66% of the variance in cigarette and cannabis use. Broad shared environmental factors (shared+special twin) played a more significant role in EA (23-29%) than AA (2-15%) women. In AA women, the influence of non-shared environment was more pronounced (42-45% vs. 11-19% in EA women). There was strong evidence for the same familial influences underlying use of both substances (rA=0.82-0.89; rC+T=0.70-0.75). Non-shared environmental factors were also correlated but less so (rE=0.48-0.66). No racial/ethnic differences were apparent in these sources of covariation.Conclusion: Heritability of cigarette and cannabis use is comparable across racial/ethnic groups. Differences in the contribution of shared and non-shared environmental influences indicate that different factors may shape substance use in EA and AA women. [ABSTRACT FROM AUTHOR]

This article is based on an in-depth interview with a pair of twins diagnosed with selective mutism and their parents 2 years after recovery. Selective mutism (SM) is a rare disorder, and identical twins sharing the condition are extremely rare. The twins developed SM simultaneously during their first year of school. The treatment and follow-up they received for several years are briefly described in this article. The interview explored the children’s and their parents’ narratives about the origin of the condition, the challenges it entailed in their daily lives, and what they found helpful in the treatment they were offered. In the interview, the children conveyed experiences that even the parents were unaware of and revealed examples of daily life-traumas for which they were unable to obtain support and help. The whole family was trapped in the silence. The twins and their parents emphasized different aspects in terms of what they believed were helpful. The implications of these findings for our understanding and treatment of children with SM are discussed, as well as the potential of service user involvement in child and adolescent mental health research. [ABSTRACT FROM AUTHOR]

Bidirectional pathways between twin relationship quality and friendship quality were investigated in a large longitudinal twin cohort. We examined negative and positive relationship features in 313 monozygotic (MZ) twins and 238 same-sex dizygotic (DZ) twins from ages 13 to 14 years, using latent structural modeling. Results showed stronger stability of the twin relationship quality compared to friendship quality. Positive features in the sibling relationship were associated with increased positive features in the relationship with the best friend a year later. In contrast, no significant association between negative sibling relationship features and change in negative friendship quality features was found. These findings speak to the important role of the sibling relationship in the development of good quality friendship relations in twins. [ABSTRACT FROM AUTHOR]

Previous studies suggest strong associations between exposure to weight-conscious peer groups and increased levels of disordered eating. This association has been attributed to socialization effects (i.e., membership leads to disordered eating); however, selection effects (i.e., selecting into peer groups based on genetic and/or environmental predispositions toward disordered eating) could contribute to or even account for these associations. The current study was the first to use a co-twin control design to disentangle these types of selection factors from socialization effects. Participants included 610 female twins (ages 8-14) drawn from the Michigan State University Twin Registry. To comprehensively examine a range of eating pathology, several disordered eating attitudes and behaviors (e.g., body dissatisfaction, binge eating) were examined via self-report questionnaires. Questionnaires also were used to assess peer group emphasis on body weight and shape. Replicating previous results, significant individual-level associations were found between membership in weight-conscious peer groups and disordered eating. However, co-twin control analyses indicated that these associations were largely due to genetic and/or shared environmental selection factors rather than pure socialization effects. Importantly, results remained unchanged when controlling for pubertal status, suggesting that effects do not vary across developmental stage. Overall, these findings question whether associations between weight-conscious peer groups and disordered eating are due entirely to socialization processes. Future studies are needed to identify the specific genetic and/or shared environmental factors that may drive selection into weight-conscious peer groups. [ABSTRACT FROM AUTHOR]

This paper examines the link between schooling and health. We provide new evidence on the relationship between formal schooling completed and several aspects of health by using Finnish twin data matched to individual information on schooling. Health is measured in 1990 (and 1981). Schooling is defined using comprehensive register-based information. All models account for initial health endowment in 1975. The sample sizes vary from 2542 to 4402 identical twins, depending on the specification. Using twin design, we find that unobserved family and genetic factors drive the cross-sectional correlations between schooling and many health measures, especially for females. Our within-MZ twin results for males show that high school (or vocational) or lowest level tertiary education reduces BMI and medication use. High school (or vocational) or university graduated males also exercise more than males who have completed primary education only. Given that high school or basic tertiary education have the strongest positive health effects for males, our results suggest that policies that prevent secondary school dropout alone may yield social benefits in the form of better health. [ABSTRACT FROM AUTHOR]

Objective: The authors investigated the relative importance of genetic and environmental influences on perinatal depression, and the genetic overlap between perinatal depression and nonperinatal depression.Method: Analyses were conducted using structural equation modeling for 1) the lifetime version of the Edinburgh Postnatal Depression Scale in 3,427 Swedish female twins and 2) clinical diagnoses of depression separated into perinatal depression and nonperinatal depression in a Swedish population-based cohort of 580,006 sisters.Results: In the twin study, the heritability of perinatal depression was estimated at 54% (95% CI=35%-70%), with the remaining variance attributable to nonshared environment (46%; 95% CI=31%-65%). In the sibling design, the heritability of perinatal depression was estimated at 44% (95% CI=35%-52%) and the heritability of nonperinatal depression at 32% (95% CI=24%-41%). Bivariate analysis showed that 14% of the total variance (or 33% of the genetic variance) in perinatal depression was unique for perinatal depression.Conclusions: The heritability of perinatal depression was estimated at 54% and 44%, respectively, in separate samples, and the heritability of nonperinatal depression at 32%. One-third of the genetic contribution was unique to perinatal depression and not shared with nonperinatal depression, suggesting only partially overlapping genetic etiologies for perinatal depression and nonperinatal depression. The authors suggest that perinatal depression constitutes a subset of depression that could be prioritized for genomic discovery efforts. The study findings have direct translational impact that can assist clinicians in the counseling of their patients regarding risk and prognosis of perinatal depression. [ABSTRACT FROM AUTHOR]

We estimated the temporal course of posttraumatic stress disorder (PTSD) in Vietnam-era veterans using a national sample of male twins with a 20-year follow-up. The complete sample included those twins with a PTSD diagnostic assessment in 1992 and who completed a DSM-IV PTSD diagnostic assessment and a self-report PTSD checklist in 2012 (n = 4,138). Using PTSD diagnostic data, we classified veterans into 5 mutually exclusive groups, including those who never had PTSD, and 4 PTSD trajectory groups: (a) early recovery, (b) late recovery, (c) late onset, and (d) chronic. The majority of veterans remained unaffected by PTSD throughout their lives (79.05% of those with theater service, 90.85% of those with nontheater service); however, an important minority (10.50% of theater veterans, 4.45% of nontheater veterans) in 2012 had current PTSD that was either late onset (6.55% theater, 3.29% nontheater) or chronic (3.95% theater, 1.16% nontheater). The distribution of trajectories was significantly different by theater service (p < .001). PTSD remains a prominent issue for many Vietnam-era veterans, especially for those who served in Vietnam. [ABSTRACT FROM AUTHOR]

The study of twin behavior offers the opportunity to study differential patterns of social and communicative interactions in a context where the adult partner and same-age peer are equally familiar. We investigated the development of social engagement, communicative gestures, and imitation in 7- to 25-month-old twins. Twin dyads (N=20 pairs) participated in 10-min, semi-structured play sessions, with the mother seated in a chair completing paperwork for half the session, and on the floor with her children for the other half. Overall, twins engaged more with their mothers than with their siblings: they showed objects and imitated speech and object use more frequently when interacting with their mothers than with their siblings. When the mother was otherwise engaged, the twins played with toys separately, observed each other's toy play, or were unengaged. These results demonstrate that adult scaffolding of social interactions supports increased communicative bids even in a context where both familiar peers and adults are available as communicative partners. [ABSTRACT FROM AUTHOR]

Increased utilization of in vitro fertilization (IVF) to treat infertility has resulted in a growing twin birthrate. Despite early childhood risks, twins have fewer psychosocial problems in middle childhood than singleton children. This study proposes that parents' conformity expectations for children have differential effects on parent-child relationships for twin and singleton children, which indirectly explains twins' more optimum psychosocial adjustment. Parental conformity expectations, parent-child relationship satisfaction, and children's emotional, behavioral, and attention problems were assessed in a sample of 288 6- to 12-year-old IVF-conceived twins and singletons. Overall, parents of twins had higher expectations for child conformity to parent rules than singleton parents. Path models demonstrate that twin status and parental expectations for child conformity interact to influence parent-child relationships, and this interaction indirectly accounted for differences in twins' and singletons' psychosocial adjustment. Findings suggest parenting constructs have differential influences on the association between twin status and parent-child relationships. Parenting research, predominantly conducted with singletons, should be reexamined before applying existing research to twin children and their families. [ABSTRACT FROM AUTHOR]

Sleep disturbances regularly co-occur with clinical psychotic disorders and dimensions of psychotic-like experiences (PLEs). One possible explanation for this, which has yet to be tested, is that similar genetic or environmental influences underlie sleep disturbances and vulnerability to PLEs. We conducted a twin study to test this possibility in relation to sleep disturbances and six specific PLEs in adolescence in the general population. Approximately 5,000 16-year-old twin pairs completed the Pittsburgh Sleep Quality Index and Insomnia Severity Index. PLEs were assessed using the Specific PLEs Questionnaire, comprising five self-report subscales (Paranoia, Hallucinations, Cognitive Disorganization, Grandiosity, and Anhedonia) and one parent-report subscale (Negative Symptoms). The associations between these measures were tested using structural equation twin model fitting. Paranoia, Hallucinations, and Cognitive Disorganization displayed moderate and significant correlations with both sleep measures (0.32-.42), while Negative Symptoms, Anhedonia, and Grandiosity showed lower correlations (0.01-0.17). Genetic and environmental influences significantly overlapped across PLEs (Paranoia, Hallucinations, Cognitive Disorganization) and both types of sleep disturbance (mean genetic and nonshared environmental correlations = 0.54 and 0.24, respectively). These estimates reduced, yet remained significant, after controlling for negative affect. The association between PLEs with sleep disturbances in adolescence is partly due to genetic and environmental influences that are common to them both. These findings indicate that the known neurobiology of sleep disturbance may provide clues regarding the causes of PLEs in adolescence. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the effects of genetic and environmental factors on sense of coherence (SOC) in young adulthood and whether family environment measured in childhood modifies these effects. Methods: SOC was measured at 20-27 years of age in 3,193 Finnish twins using the Antonovsky's 13-item short scale. The twins and their parents had rated their emotional family environment independently when the twins were 12 years of age. The data were analyzed using applications of structural linear equation modeling to twin data. Results: Females rated SOC 2.42 points lower than males. Additive genetic factors explained 39 % of the variation of SOC in males and 49 % in females, whereas the rest of the variation was explained by environmental factors unique to each twin individual. For the dimensions of SOC, the highest genetic correlation was found between comprehensibility and manageability (0.90 in males and 0.97 in females). SOC was strongest in the participants who had reported supportive family atmosphere and low relational tensions to parents in childhood. These participants also had higher genetic variance and lower unique environmental variance of SOC when compared to those who reported emotionally more stressful family environment. The results were similar when we used parental rating of family environment. Conclusion: Genetic factors are important for SOC, but genetic influences are much greater in supportive family environments. This emphasizes the importance of childhood home for the development of strong SOC. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to do a psychometric evaluation of the somatic and psychological health report (SPHERE) among Chinese adolescents. Our participants were 116 twins (50 females). Psychometric evaluation indicated that the reliability and validity of this scale were good. The internal consistencies and split-half reliabilities of all subscales were above 0.80. Furthermore, the item-total correlations were acceptable for all the subscales (all the values were higher than 0.20). The present findings suggest that the SPHERE can be well used to measure Chinese adolescents’ somatic and psychological health. [ABSTRACT FROM PUBLISHER]

Recent research demonstrates that a wide range of political attitudes, beliefs, and behaviors can be explained in part by genetic variation. However, these studies have not yet identified the mechanisms that generate such a relationship. Some scholars have speculated that psychological traits mediate the relationship between genes and political participation, but so far there have been no empirical tests. Here we focus on the role of three psychological traits that are believed to influence political participation: cognitive ability, personal control, and extraversion. Utilizing a unique sample of more than 2,000 Swedish twin pairs, we show that a common genetic factor can explain most of the relationship between these psychological traits and acts of political participation, as well as predispositions related to participation. While our analysis is not a definitive test, our results suggest an upper bound for a proposed mediation relationship between genes, psychological traits, and political participation. [ABSTRACT FROM AUTHOR]

Several influential psychologists have attempted to estimate to what extent human happiness levels are directly controlled by genes by comparing the happiness levels of identical twins raised apart. If we discover that the happiness levels of identical twins raised apart tend to be closer than the happiness levels of fraternal twins raised apart, this is taken as evidence that average happiness levels are largely controlled by genes. However, if it turns out that identical twins' happiness levels tend to be substantially different, as different as fraternal twins raised apart, it has been argued that this implies that the environment largely determines happiness levels. I contend that this interpretation of the data rests on a set of questionable, closely related assumptions: a) that pairs of identical twins raised apart are raised in substantially different environments; b) that genetically identical twins aren't identical in other pertinent ways; and c) that average levels of affect that are correlated with certain sets of genes in the environments the twin studies were conducted in will be correlated with those genes in other relevant environments because those genes govern average affect levels. In this paper, I will show that these assumptions are false and explain how to properly go about investigating the contingent causal links between genes and happiness. In the end, I argue that there is no good evidence that our genes delimit our hedonic potential and that the fact that this misinterpretation of the data has been widely disseminated is potentially harmful to human well-being. [ABSTRACT FROM PUBLISHER]

Aims Multiple forms of drug abuse/dependence frequently co-occur with problem/pathological gambling ( PPG). The current study examines the extent to which genetic and environmental factors contribute to their co-occurrence. Design Bivariate models investigated the magnitude and correlation of genetic and environmental contributions to problem/pathological gambling and its co-occurrence with nicotine dependence, cannabis abuse/dependence and stimulant abuse/dependence. Setting Computer-assisted telephone interviews in the community. Participants Participants were 7869 male twins in the Vietnam Era Twin Registry, a USA-based national twin registry. Measurements Life-time DSM- III- R diagnoses for problem/pathological gambling, nicotine dependence, cannabis abuse/dependence and stimulant abuse/dependence were determined using the Diagnostic Interview Schedule. Findings All drug-use disorders displayed additive genetic and non-shared environmental contributions, with cannabis abuse/dependence also displaying shared environmental contributions. Both genetic [genetic correlation r A = 0.22; 95% confidence interval ( CI) = 0.10-0.34] and non-shared environmental components (environmental correlation r E = 0.24; 95% CI = 0.10-0.37) contributed to the co-occurrence of problem/pathological gambling and nicotine dependence. This pattern was shared by cannabis abuse/dependence ( r A = 0.32; 95% CI = 0.05-1.0; r E = 0.36; 95% CI = 0.16-0.55) but not stimulant abuse/dependence ( SAD), which showed only genetic contributions to the co-occurrence with problem/pathological gambling ( r A = 0.58; 95% CI = 0.45-0.73). Conclusions Strong links between gambling and stimulant-use disorders may relate to the neurochemical properties of stimulants or the illicit nature of using 'hard' drugs such as cocaine. The greater contribution of environmental factors to the co-occurrence between problem/pathological gambling and 'softer' forms of drug abuse/dependence (cannabis, tobacco) suggest that environmental interventions (perhaps relating to availability and legality) may help to diminish the relationship between problem/pathological gambling and tobacco- and cannabis-use disorders. [ABSTRACT FROM AUTHOR]

Objectives Emotional processing difficulties are potential risk markers for eating disorders that are also present after recovery. The aim of this study was to examine these traits in twins with eating disorders. Methods The Reading the Mind in the Eyes test, Emotional Stroop task and the Difficulties in Emotion Regulation Scale were administered to 112 twins with and without eating disorders (DSM IV-TR eating disorder criteria). Generalised estimating equations compared twins with eating disorders against unaffected co-twins and control twins, and within-pair correlations were calculated for clinical monozygotic ( n = 50) and dizygotic twins ( n = 20). Results Emotion recognition difficulties, attentional biases to social threat and difficulties in emotion regulation were greater in twins with eating disorders, and some were present in their unaffected twin siblings. Evidence for a possible genetic basis was highest for emotion recognition and attentional biases to social stimuli. Conclusion Emotion recognition difficulties and sensitivity to social threat appear to be endophenotypes associated with eating disorders. However, the limited statistical power means that these findings are tentative and require further replication. Copyright © 2013 John Wiley & Sons, Ltd and Eating Disorders Association. [ABSTRACT FROM AUTHOR]

Research suggests that sibling-peer connections are important for understanding adolescent problem behaviors. Using a novel behavioral genetic design, the current study investigated peer network overlap in 300 child-child pairs (aged 7-13 years) in 5 dyad types: monozygotic ( MZ), dizygotic twins, full siblings ( FSs), friend pairs, and virtual twins (i.e., same-aged, genetically unrelated siblings). Genetic relatedness, sex composition, and age differences contributed to peer overlap in sibling dyads. MZ twins showed the highest overlap (82%), opposite-sex FS pairs showed the lowest overlap (27%), and friend pairs (48%) were close to the mean (53%). Social contact variables and self-reported relationship intimacy predicted additional variance in peer overlap. The roles of genotype-environment correlational and shared environmental processes in the sibling-peer connections are discussed. [ABSTRACT FROM AUTHOR]

In order to estimate the influence of genetic and environmental factors on 'crying without a cause' and 'being easily upset' in 2-year-old children, a large twin study was carried out. Prospective data were available for ~18,000 2-year-old twin pairs from the Netherlands Twin Register. A bivariate genetic analysis was performed using structural equation modeling in the Mx software package. The influence of maternal personality characteristics and demographic and lifestyle factors was tested to identify specific risk factors that may underlie the shared environment of twins. Furthermore, it was tested whether crying without a cause and being easily upset were predictive of later internalizing, externalizing and attention problems. Crying without a cause yielded a heritability estimate of 60% in boys and girls. For easily upset, the heritability was estimated at 43% in boys and 31% in girls. The variance explained by shared environment varied between 35% and 63%. The correlation between crying without a cause and easily upset (r = .36) was explained both by genetic and shared environmental factors. Birth cohort, gestational age, socioeconomic status, parental age, parental smoking behavior and alcohol use during pregnancy did not explain the shared environmental component. Neuroticism of the mother explained a small proportion of the additive genetic, but not of the shared environmental effects for easily upset. Crying without a cause and being easily upset at age 2 were predictive of internalizing, externalizing and attention problems at age 7, with effect sizes of .28-.42. A large influence of shared environmental factors on crying without a cause and easily upset was detected. Although these effects could be specific to these items, we could not explain them by personality characteristics of the mother or by demographic and lifestyle factors, and we recognize that these effects may reflect other maternal characteristics. A substantial influence of genetic factors was found for the two items, which are predictive of later behavioral problems. [ABSTRACT FROM AUTHOR]

Sex differences in mental rotation ability have been observed in many countries. A previous study of Finnish participants reported that genetic and environmental influences on mental rotation ability differ between sexes. In this study, we assessed genetic and environmental influences on variance in mental rotation ability in 649 Japanese twins using a mental rotation test. To explain the influence of sex on variance in mental rotation ability, we applied genetic analysis using the sex limitation model. The following two factors explained variance in mental rotation ability: (1) the additive genetic factor, which reflects the accumulated small influence of many genes, and (2) the unique environmental factor, which is a type of environmental factor that differs between co-twins. The shared environmental factor, a type of environmental factor common for co-twins, could not explain the variance in mental rotation ability. Furthermore, the additive genetic factor was the same between sexes (i.e., not qualitative sex differences for the additive genetic factor), indicating that the same genes affect mental rotation ability in both sexes. Despite this observation, the additive genetic influence was greater in males than in females. In contrast, the unique environmental influence was not different between sexes. Considering the current results and those of a previous study, the quantitative sex difference for the additive genetic influences in mental rotation ability may be universal, while the unique environmental differences may depend on the characteristics of specific populations. [ABSTRACT FROM AUTHOR]

Background: There is currently little evidence concerning the impact of the inter-twin relationship on behavioral outcomes and yet the twin relationship is frequently hypothesized to be a unique source of psychopathology in twins. The current study asked whether the inter-twin relationship is a predictor of behavioral difficulties and whether there are zygosity differences in this relationship.Method: An Australian sample of same sex twins (N = 356, 164 MZ and 192 DZ) was studied in the year prior to school (Time 1) and again in first year of school (Time 2). Associations between twin-relationship and behavior problems were examined via path-analysis, and Satorra-Bentler chi-square difference tests were used to compare twins across zygosity.Results: Results show that both conflict and lower levels of warmth at Time 1 were predictive of hyperactivity and conduct disorder at Time 2, but they were not associated with emotional difficulties or peer problems. While DZ twins shared less warmth than MZ twins, there were no differences in behavior problems.Conclusion: Conflict and lower levels of warmth in the inter-twin relationship are associated with hyperactivity and conduct disorder and may serve as important considerations when making decisions regarding class separation at entry to school. [ABSTRACT FROM AUTHOR]

The present study investigated the genetic and environmental covariance between psychopathic personality traits with reactive and proactive aggression in 9- to 10-year-old twins (N = 1,219). Psychopathic personality traits were assessed with the Child Psychopathy Scale (D. R. Lynam, 1997), while aggressive behaviors were assessed using the Reactive Proactive Questionnaire (A. Raine et al., 2006). Significant common genetic influences were found to be shared by psychopathic personality traits and aggressive behaviors using both caregiver (mainly mother) and child self-reports. Significant genetic and nonshared environmental influences specific to psychopathic personality traits and reactive and proactive aggression were also found, suggesting etiological independence among these phenotypes. Additionally, the genetic relation between psychopathic personality traits and aggression was significantly stronger for proactive than reactive aggression when using child self-reports. [ABSTRACT FROM AUTHOR]

Stressful events early in life can affect children's mental health problems. Collecting valid and reliable information about children's bad experiences is important for research and clinical purposes. This study aimed to (1) investigate whether mothers and children provide valid reports of bullying victimization, (2) examine the inter-rater reliability between the two informants, (3) test the predictive validity of their reports with children's emotional and behavioral problems and (4) compare the genetic and environmental etiology of bullying victimization as reported by mothers and children. We assessed bullying victimization in the Environmental-Risk (E-Risk) Longitudinal Twin Study, a nationally-representative sample of 1,116 families with twins. We collected reports from mothers and children during private interviews, including detailed narratives. Findings showed that we can rely on mothers and children as informants of bullying victimization: both informants provided information which adhered to the definition of bullying as involving repeated hurtful actions between peers in the presence of a power imbalance. Although mothers and children modestly agreed with each other about who was bullied during primary and secondary school, reports of bullying victimization from both informants were similarly associated with children's emotional and behavioral problems and provided similar estimates of genetic and environmental influences. Findings from this study suggest that collecting information from multiple informants is ideal to capture all instances of bullying victimization. However, in the absence of child self-reports, mothers can be considered as a viable alternative, and vice versa. [ABSTRACT FROM AUTHOR]

Objectives. Despite the well-replicated finding that neuroticism is associated with increased susceptibility for psychopathology, it remains unclear what 'vulnerability as indexed by neuroticism' represents in terms of everyday life emotional processes. This study examined the association between neuroticism and six phenotypes of daily life emotional responses: positive affect (PA), negative affect (NA), PA variability, NA variability, stress sensitivity, and reward experience, and investigated the contribution of genetic and environmental factors to these associations. Design. A prospective cohort study in a population-based sample of 416 adult female twins. Method. A momentary assessment approach (experience sampling method) was used to collect multiple assessments of affect in daily life. Neuroticism was assessed with the Eysenck Personality Scale. Multi-level regression analyses were carried out to examine the association between neuroticism and the phenotypes of daily life emotional responses. Cross-twin, cross-trait analyses, and bivariate structural equation modelling (SEM) were performed in order to investigate the nature of these associations. Results. A high neuroticism scorewas associated with lowermomentary PA levels and increased NA variability, independent of momentary NA, PA variability, stress sensitivity, and reward experience. Both the cross-twin, cross-trait analyses, and the bivariate SEM showed that unique, non-shared environmental factors drive the association between neuroticism and PA and that the association between neuroticism and increased NA variability is based on shared genetic factors as well as individual-specific environmental factors. Conclusions. Neuroticism as measured by Eysenck questionnaire may index an environmental risk for decreased daily life PA levels and a genetic as well as an environmental risk for increased NA variability. Decomposing the broad measure of neuroticism into measurable persons-context interactions increases its 'informative' value in explaining psychopathology. [ABSTRACT FROM AUTHOR]

Copy number variations (CNVs) are common structural variations in the human genome that strongly affect genomic diversity and can play a role in the development of several diseases, including neurodevelopmental disorders. Recent reports indicate that monozygotic twins can show differential CNV profiles. We searched CNVs in monozygotic twins discordant for schizophrenia to identify susceptible loci for schizophrenia. Three pairs of monozygotic twins discordant for schizophrenia were subjected to analysis. Genomic DNA samples were extracted from peripheral blood lymphocytes. We adopted the Affymetrix Genome-Wide Human SNP (Single Nucleotide Polymorphism) Array 6.0 to detect copy number discordance using Partek Genomics Suite 6.5 beta. In three twin pairs, however, validations by quantitative PCR and DNA sequencing revealed that none of the regions had any discordance between the three twin pairs. Our results support the hypothesis that epigenetic changes or fluctuation in developmental process triggered by environmental factors mainly contribute to the pathogenesis of schizophrenia. Schizophrenia caused by strong genetics factors including copy number alteration or gene mutation may be a small subset of the clinical population. [ABSTRACT FROM AUTHOR]

Health is a multidimensional and continual concept. Traditional latent analytic approaches have inherent deficits in capturing the complex nature of the concept; however, the Grade of Membership (GoM) model is well suited for this problem. We applied the GoM method to a set of 31 indicators to construct ideal profiles of health status based on physical, mental and social support items among 848 adult twins from Qingdao, China. Four profiles were identified: healthy individuals (pure type I), individuals with personality disorders (pure type II), individuals with mental impairments (pure type III) and individuals with physical impairments (pure type IV). The most frequently occurring combination in this population was profiles I, II, IV (14.74%), followed by profiles I, II, III, IV (13.44%), and then type I (11.08%). Only 13.56% of subjects fell completely into one single pure type, most individuals exhibited some of the characteristics of two or more pure types. Our results indicated that, compared to conventional statistical methods, the GoM model was more suited to capture the complex concept of health, reflecting its multidimensionality and continuity, while also exhibiting preferable reliability. This study also made an important contribution to research on GoM application in non-independent samples. [ABSTRACT FROM AUTHOR]

We examined the variation and heritability of DSM-IV nicotine withdrawal (NW) in adult and adolescent male and female twin cigarette smokers (who reported smoking 100 or more cigarettes lifetime). Telephone diagnostic interviews were completed with 3,112 Australian adult male and female smokers (53% women; age: 24-36) and 702 Missouri adolescent male and female smokers (59% girls; age: 15-21). No gender or cohort differences emerged in rates of meeting criteria for NW (44%). Latent class analyses found that NW symptoms were best conceptualized as a severity continuum (three levels in adults and two levels in adolescents). Across all groups, increasing NW severity was associated with difficulty quitting, impairment following cessation, heavy smoking, depression, anxiety, conduct disorder and problems with alcohol use. NW was also associated with seeking smoking cessation treatment and with smoking persistence in adults. The latent class structure of NW was equally heritable across adult and adolescent smokers with additive genetic influences accounting for 49% of the variance and the remaining 51% of variance accounted for by unique environmental influences. Overall, findings suggest remarkable similarity in the pattern and heritability of NW across adult and adolescent smokers, and highlight the important role of NW in psychiatric comorbidity and the process of smoking cessation across both age groups. [ABSTRACT FROM AUTHOR]

Research on twin-singleton differences in externalizing and internalizing problems in childhood is largely cross-sectional and yields contrasting results. The goal of this study was to compare developmental trajectories of externalizing and internalizing problems in 6- to 12-year-old twins and singletons. Child Behavior Checklist (CBCL) maternal reports of externalizing and internalizing problems were obtained for a sample of 9651 twins from the Netherlands Twin Register and for a representative general population sample of 1351 singletons. Latent growth modeling was applied to estimate growth curves for twins and singletons. Twin-singleton differences in the intercepts and slopes of the growth curves were examined. The developmental trajectories of externalizing problems showed a linear decrease over time, and were not significantly different for twins and singletons. Internalizing problems seem to develop similarly for twins and singletons up to age 9. After this age twins' internalizing symptoms start to decrease in comparison to those of singletons, resulting in less internalizing problems than singletons by the age of 12 years. Our findings confirm the generalizability of twin studies to singleton populations with regard to externalizing problems in middle and late childhood. The generalizability of studies on internalizing problems in early adolescence in twin samples should be addressed with care. Twinship may be a protective factor in the development of internalizing problems during early adolescence. [ABSTRACT FROM AUTHOR]

Background: Negative parenting practices may be an environmental risk factor for subsequent conduct problems. Research on the association between parenting practices and callous-unemotional traits, a risk factor for conduct problems, has produced mixed findings.Aims: To investigate whether negative parental discipline is a non-shared environmental risk factor for the development of conduct problems and callous-unemotional traits.Method: Longitudinal, multi-informant data from a community sample of twins were analysed using the monozygotic (MZ) twin differences design for 4508 twins (2254 twin pairs).Results: Within MZ twin pairs, the twin receiving more negative parental discipline at 7 years had more conduct problems (but not more callous-unemotional traits) at 12 years.Conclusions: During the transition to early adolescence, negative parental discipline operates as a non-shared environmental risk factor for development of conduct problems, but not for the development of callous-unemotional traits. [ABSTRACT FROM AUTHOR]

Twin studies are well known for their value in quantifying the contribution of genes to population variation in behaviors and personality traits. Twin studies also provide a unique opportunity to untangle the contribution of environmental experiences to emotional and behavioral development. This is particularly true when examining monozygotic (MZ) twins since they represent a pair of individuals naturally matched on both their genetic background and their shared environment, thus allowing the identification of environmental experiences unique to each twin which may impact developmental outcome. This article presents two analytical strategies based on the discordant MZ-twin method. It stresses the power of this method to establish plausible causal pathways between environmental factors and developmental outcomes, and provides examples from the socio- developmental literature to illustrate its application. It also describes the limitations of this method and its requirements for optimal utilization. [ABSTRACT FROM AUTHOR]

The goals, prospects and methods of the Prospective Twin Registry in Southwestern China (TRiSC) are described. The aim of this study is to measure children's behavioral development and psychopathology from phenotypic, genetic and environmental perspectives. It focuses on measuring children's behavior and psychopathology from child self-reports, as well as parental and teacher informant reports, and relating it to the children's general cognitive abilities, and to the parenting style in the family. Other variables of interest such as children's temperament and parental health status are discussed, as well as plans for further research. [ABSTRACT FROM AUTHOR]