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Background: Shame is considered a maladaptive self‐conscious emotion that commonly co‐occurs alongside depression and anxiety. Little is known, however, about the aetiology of shame and its associations with depression and anxiety. We estimated, for the first time, genetic and environmental influences on shame and on its associations with depression and anxiety in adolescence. Methods: The sample was twin and sibling pairs from the Genesis 1219 Study (Time 1, N = 2,685; males 42.8%, Mage = 14.95, SD = 1.67, age range: 12–21; Time 2, N = 1618; males 39.7%, Mage = 16.97, SD = 1.64, age range: 14–23). Participants completed validated questionnaires to measure shame (at Time 1), depression and anxiety (at Times 1 and 2). Results: Shame was moderately to strongly associated with concurrent depression and anxiety. Prospectively, shame was significantly associated with an increase in depression, but not anxiety. Genetic analyses revealed that shame was moderately heritable with substantial nonshared environmental influence. The associations between shame and concurrent depression and anxiety were primarily accounted for by overlapping genetic influences. Prospectively, the association between shame and later depression was primarily accounted for by genetic and nonshared environmental influences shared with earlier depression. The unique association between shame and later depression was mostly explained by common nonshared environmental influences. Conclusions: The findings offer novel evidence regarding aetiology of shame—although moderately heritable, shame in adolescents may also result from nonshared environmental factors. Genetic and nonshared environmental influences contribute to the co‐occurrence of shame with depression and anxiety. [ABSTRACT FROM AUTHOR]

Background: Children in the UK go through rigorous teacher assessments and standardized exams throughout compulsory (elementary and secondary) education, culminating with the GCSE exams (General Certificate of Secondary Education) at the age of 16 and A‐level exams (Advanced Certificate of Secondary Education) at the age of 18. These exams are a major tipping point directing young individuals towards different lifelong trajectories. However, little is known about the associations between teacher assessments and exam performance or how well these two measurement approaches predict educational outcomes at the end of compulsory education and beyond. Methods: The current investigation used the UK–representative Twins Early Development Study (TEDS) sample of over 5,000 twin pairs studied longitudinally from childhood to young adulthood (age 7–18). We used teacher assessment and exam performance across development to investigate, using genetically sensitive designs, the associations between teacher assessment and standardized exam scores, as well as teacher assessments' prediction of exam scores at ages 16 and 18, and university enrolment. Results: Teacher assessments of achievement are as reliable, stable and heritable (~60%) as test scores at every stage of the educational experience. Teacher and test scores correlate strongly phenotypically (r ~ .70) and genetically (genetic correlation ~.80) both contemporaneously and over time. Earlier exam performance accounts for additional variance in standardized exam results (~10%) at age 16, when controlling for teacher assessments. However, exam performance explains less additional variance in later academic success, ~5% for exam grades at 18, and ~3% for university entry, when controlling for teacher assessments. Teacher assessments also predict additional variance in later exam performance and university enrolment, when controlling for previous exam scores. Conclusions: Teachers can reliably and validly monitor students' progress, abilities and inclinations. High‐stakes exams may shift educational experience away from learning towards exam performance. For these reasons, we suggest that teacher assessments could replace some, or all, high‐stakes exams. [ABSTRACT FROM AUTHOR]

Background: Little is known about genetic and environmental influences on the components of disruptive mood dysregulation disorder (DMDD), tonic irritability (i.e., irritable mood) and phasic irritability (i.e., temper outbursts). This study examined prevalence, stability, and heritability of tonic irritability, phasic irritability, and a DMDD proxy (pDMDD) based on DSM‐5 criteria. Methods: pDMDD was derived using data from clinical interviews of parents and their twins (N = 1,431 twin pairs), ages 8–17, participating in Waves 1 and 2 of the Virginia Twin Study of Adolescent Behavioral Development. Biometrical modeling was used to compare a common pathway model (CPM) and an independent pathway model (IPM), and heritability estimates were obtained for pDMDD using the symptoms of irritable mood (tonic irritability; DMDD Criterion D), intense temper outbursts (phasic irritability; DMDD Criterion A), and frequent temper outbursts (phasic irritability; DMDD Criterion C). Results: Lifetime prevalence of pDMDD was 7.46%. The stability of DMDD symptoms and the pDMDD phenotype across approximately one year were moderate (.30–.69). A CPM was a better fit to the data than an IPM. Phasic irritability loaded strongly onto the pDMDD latent factor (.89–.96) whereas tonic irritability did not (.28). Genetic influences accounted for approximately 59% of the variance in the latent pDMDD phenotype, with the remaining 41% of the variance due to unique environmental effects. The heritability of tonic irritability (54%) was slightly lower than that of frequent and intense temper (components of phasic irritability; 61% and 63%, respectively). Conclusions: Compared to tonic irritability, phasic irritability appears to be slightly more stable and heritable, as well as a stronger indicator of the latent factor. Furthermore, environmental experiences appear to play a substantial role in the development of irritability and DMDD, and researchers should seek to elucidate these mechanisms in future work. [ABSTRACT FROM AUTHOR]

Objective: Early detection of binge‐eating (BE) behaviors and their risk factors is associated with better outcomes. A multi‐informant approach for assessing BE psychopathology and risk factors has been emphasized to increase the probability and accuracy of early detection. Impulsivity (particularly negative and positive urgency), trait anxiety, and depressive symptoms are associated with BE behaviors. The present study examined maternal‐child convergence of reports of child BE, impulsivity, trait anxiety, and depressive symptoms and examined the predictive power of maternal reports for child‐reported BE behaviors. Method: Participants included 927 female twins (aged 8–16 years) and 468 mothers from the Michigan State University Twin Registry. Risk factors and BE were assessed with self‐report questionnaires. Results: Intraclass correlation coefficients showed fair‐to‐moderate inter‐rater agreement (ICCs =.31–.41) between maternal and child reports of risk factors and low‐to‐fair agreement for BE (ICCs =.05–.29). Controlling for the effects of age, pubertal status, body mass index, and family relatedness, multilevel models showed that maternal reports of child impulsivity, anxiety, and depressive symptoms did not add predictive power above and beyond child reports. Discussion: Results call into question the utility and practical implications of using maternal reports to supplement child reports for BE and its risk factors. [ABSTRACT FROM AUTHOR]

Background: Callous‐Unemotional (CU) and psychopathic traits are consistently associated with impaired recognition of others' emotions, specifically fear and sadness. However, no studies have examined whether the association between CU traits and emotion recognition deficits is due primarily to genetic or environmental factors. Methods: The current study used data from 607 Caucasian twin pairs (N = 1,214 twins) to examine the phenotypic and genetic relationship between the Inventory of Callous‐Unemotional Traits (ICU) and facial emotion recognition assessed via the laboratory‐based Facial Expression Labeling Task (FELT). Results: The uncaring/callous dimension of the ICU was significantly associated with impaired recognition of happiness, sadness, fear, surprise, and disgust. The unemotional ICU dimension was significantly associated with improved recognition of surprise and disgust. Total ICU score was significantly associated with impaired recognition of sadness. Significant genetic correlations were found for uncaring/callous traits and distress cue recognition (i.e. fear and sadness). The observed relationship between uncaring/callous traits and deficits in distress cue recognition was accounted for entirely by shared genetic influences. Conclusions: The results of the current study replicate previous findings demonstrating impaired emotion recognition among youth with elevated CU traits. We extend these findings by replicating them in an epidemiological sample not selected or enriched for pathological levels of CU traits. Furthermore, the current study is the first to investigate the genetic and environmental etiology of CU traits and emotion recognition, and results suggest genetic influences underlie the specific relationship between uncaring/callous traits and distress cue (fear/sadness) recognition in others. [ABSTRACT FROM AUTHOR]

Aims: To estimate birth cohort effects on alcohol consumption and abstinence in Finland and to test differences between birth cohorts in genetic and environmental sources of variation in Finnish adult alcohol use. Design The Older Finnish Twin Cohort longitudinal survey study 1975–2011. Setting: Finland. Participants: A total of 26 121 same‐sex twins aged 18–95 years (full twin pairs at baseline n = 11 608). Measurements Outcome variables were the quantity of alcohol consumption (g/month) and abstinence (drinking zero g/month). Predictor variables were 10‐year birth cohort categories and socio‐demographic covariates. In quantitative genetic models, two larger cohorts (born 1901–20 and 1945–57) were compared. Findings: Multi‐level models in both sexes indicated higher levels of alcohol consumption in more recent birth cohorts and lower levels in earlier cohorts, compared with twins born 1921–30 (all P < 0.003). Similarly, compared with twins born 1921–30, abstaining was more common in earlier and less common in more recent cohorts (all P < 0.05), with the exception of men born 1911–20. Birth cohort differences in the genetic and environmental variance components in alcohol consumption were found: heritability was 21% [95% confidence interval (CI) = 0–56%] in the earlier‐born cohort of women [mean age 62.8, standard deviation (SD) = 5.3] and 51% (95% CI = 36–56%) in a more recent cohort (mean age 60.2, SD = 3.7) at the age of 54–74. For men, heritability was 39% (95% CI = 27–45%) in both cohorts. In alcohol abstinence, environmental influences shared between co‐twins explained a large proportion of variation in the earlier‐born cohort (43%, 95% CI = 23–63%), whereas non‐shared environmental (54%, 95% CI = 39–72%) and additive genetic influences (40%, 95% CI = 13–61%) were more important among more recent cohorts of men and women. Conclusion: The contribution of genetic and environmental variability to variability in alcohol consumption in the Finnish population appears to vary by birth cohort. [ABSTRACT FROM AUTHOR]

Takahashi et al. (2020) showed that CU traits at age 7 were highly heritable, that the genetic influences underlying the course of CU traits from age 7 to 16 were largely independent from those underlying the initial level, and that the genetic influences on CU traits in early childhood were substantially different from the genetic influences on these traits in adolescence. This commentary on these important and provocative findings focuses on their implications for future research. Specifically, it notes that future studies attempting to find genetic loci related to CU traits need to consider that such loci may differ depending on the age of the sample and this research needs to consider several important considerations when measuring CU traits that can influence the results. Further, the results of Takahashi et al highlight the importance of environmental influences on the stability of CU traits that could play an important role in treatment. [ABSTRACT FROM AUTHOR]

Background: The role of general anesthetics as a risk factor for possible neurodevelopmental disorders (NDDs) in humans is unresolved. The investigation of the role of anesthetics in the development of postgeneral anesthesia (anesthesia onward) NDDs has proven to be complicated, partly because of the inherent confounding in clinical cohort studies, and partly by the fact that anesthetics are only one part in the complex process of anesthesia‐surgery. Methods: Utilizing the Swedish databases Child and Adolescent Twins Study in Sweden (CATSS) and National Patient Register (NPR), we investigated twins discordant for anesthesia, born between 1997 and 2004 for traits of NDDs. We identified 68 twin pairs discordant for anesthesia and explored traits of Attention‐Deficit/Hyperactivity Disorder (ADHD), Learning Disability (LD), and Autism Spectrum Disorder (ASD) in them while simultaneously taking congenital abnormalities and systemic disorders (CSDs) into account. We analyzed the possible effect of anesthesia on neurodevelopmental problems, and we analyzed the within‐pair differences using conditional linear regression. Results: Twins with a recorded episode of anesthesia had higher traits of NDDs than twins without; similarly twins with CSDs had higher mean scores on all traits than twins without CSDs. The within‐pair analyses suggested that exposure to anesthesia was associated with higher scores of ADHD (regression coefficient 1.02 and 95% confidence intervals: 0.27–1.78) in monozygotic (MZ) twins discordant for anesthesia. This effect remained when adjusting for congenital abnormalities. Discussion: Our finding that traits of ADHD were slightly associated with anesthesia in a genetically sensitive design is in need of replication and warrants further investigation. Future studies should aim to elucidate mechanisms behind this possible association (e.g. anesthetics doses, age at exposure, exposure duration). [ABSTRACT FROM AUTHOR]

Increased medically assisted reproduction ( MAR) use to treat infertility has resulted in a growing twin birth rate. Little is known about parent-child relationships for twin relative to singleton children in middle childhood. This study fills this gap by examining parent-child relationships in 57 families with eighty 6- to 12-year-old MAR twin and singleton children using observational data (warm and supportive communication, control, and hostility). Nested ANCOVAs indicate that while mothers exhibit similar interactional behaviors toward twins and singletons, fathers have less optimum behaviors toward twins relative to singletons. Twins displayed less engaged behavior with mothers and fathers relative to singletons. Given the vitality of parent-child relationships for family and child adjustment, future studies should examine determinants and outcomes of twin-singleton relationship differences to bolster twins' and their families' functioning. [ABSTRACT FROM AUTHOR]

Aims To examine whether genetic influences on the development of alcohol use disorders (AUD) among men during emerging adulthood through mid-adulthood are stable or dynamic. Design A twin study modeling developmental changes in the genetic and environmental influences on AUD during three age periods (18-25, 26-33 and 33-41) as a Cholesky decomposition. Setting Sweden. Participants Swedish male twin pairs (1532 monozygotic and 1940 dizygotic) and 66 033 full male sibling pairs born less than 2 years apart. Measurements AUD was identified based on Swedish medical and legal registries. Findings The best-fitting model included additive genetic and unique environmental factors, with no evidence for shared environmental factors. Although the total heritability was stable over time, there were two major genetic factors contributing to AUD risk, one beginning at ages 18-25 with a modest decline in importance over time [0.84; confidence interval (CI) = 0.83-0.88], and another of less impact beginning at ages 26-33 with a modest increase in importance by ages 33-41 (0.31; CI = 0.05-0.47). Conclusions The heritability of alcohol use disorders among Swedish men appears to be stable among three age periods: 18-25 years, 26-33 years, and 33-41 years. Two sets of genetic risk factors contribute to alcohol use disorders risk, with one originating during the ages 18-25 years and another coming online at 26-33 years, providing support for the developmentally dynamic hypothesis. [ABSTRACT FROM AUTHOR]

Background and Objectives: We examined the associations of religious attendance during childhood (C-RA) and adulthood (A-RA) with alcohol involvement (ever drinking, timing of first alcohol use, and alcohol use disorder [AUD]) in White and Black female twins. As genetic and environmental factors influence religious attendance and alcohol involvement, we examined the extent to which they contribute to their association.Methods: Data on 3,234 White and 553 Black female twins (18-29 years) from the Missouri Adolescent Female twin Study. Significant correlations between C-RA or A-RA and alcohol involvement were parsed into their additive genetic, shared environmental, and individual-specific environmental sources.Results: C-RA was associated with ever drinking and timing of first alcohol use in Whites. A-RA was associated with ever drinking and AUD in both Whites and Blacks. Shared environmental influences did not contribute to alcohol or religiosity phenotypes in Blacks. In Whites, the association between C-RA and alcohol was due to shared environmental influences, whereas the association between A-RA and alcohol was attributable to additive genetic, shared environmental, and individual-specific environmental sources. Individual-specific environment and genetics contributed to associations between A-RA and ever drinking and AUD, respectively, in Blacks.Conclusions: Factors other than C-RA contribute to lower rates of alcohol involvement in Blacks. Shared environment does not contribute to links between A-RA and alcohol involvement in Blacks.Scientific Significance: The protective impact of childhood religiosity on alcohol use and misuse is important in Whites and is due to familial factors shared by religiosity and alcohol involvement. (Am J Addict 2017;26:437-445). [ABSTRACT FROM AUTHOR]

In this small-scale indicative study I explored the issue of individuation in relation to the life stories of a group of adult opposite-sex twins, using a psycho-social approach and a narrative interview methodology (Hollway & Jefferson, 2013). I found that none of the six interviewees reported having had a close relationship with their mother in infancy and childhood but five said they had had a close relationship with their co-twin, which endured in later life. Cleaving to the co-twin seemed to complicate and disrupt identity formation and the development of mature adult relationships. I concluded that the respondents in the study had experienced a similar psycho-social challenge to that of same-sex twins - how to honour their twinship while at the same time attempting to forge a unique identity - but that they seemed to have faced an additional challenge when it came to developing adult relationships with members of the opposite sex. [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]

Background: Reciprocal social behavior (RSB) is a developmental prerequisite for social competency, and deficits in RSB constitute a core feature of autism spectrum disorder (ASD). Although clinical screeners categorically ascertain risk of ASD in early childhood, rapid methods for quantitative measurement of RSB in toddlers are not yet established. Such measurements are critical for tracking developmental trajectories and incremental responses to intervention. Methods: We developed and validated a 20-min video-referenced rating scale, the video-referenced rating of reciprocal social behavior (vrRSB), for untrained caregivers to provide standardized ratings of quantitative variation in RSB. Parents of 252 toddler twins [Monozygotic (MZ) = 31 pairs, Dizygotic (DZ) = 95 pairs] ascertained through birth records, rated their twins' RSB at two time points, on average 6 months apart, and completed two developmental measures, the Modified Checklist for Autism in Toddlers (M-CHAT) and the MacArthur Communicative Development Inventory Short Form (MCDI-s). Results: Scores on the vrRSB were fully continuously distributed, with excellent 6-month test-retest reliability ([intraclass correlation coefficient] ICC = 0.704, p < .000). MZ twins displayed markedly greater trait concordance than DZ twins, (MZ ICC = 0.863, p < .000, DZ ICC = 0.231, p < .012). VrRSB score distributions were highly distinct for children passing versus failing the M-CHAT (t = -8.588, df = 31, p < .000), incrementally improved from 18-24 months, and were inversely correlated with receptive and expressive vocabulary on the MCDI-s. Conclusions: Like quantitative autistic trait ratings in school-aged children and adults, toddler scores on the vrRSB are continuously distributed and appear highly heritable. These ratings exhibited minimal measurement error, high inter-individual stability, and developmental progression in RSB as children matured from 18-24 months, supporting their potential utility for serially quantifying the severity of early autistic syndromes over time and in response to intervention. In addition, these findings inform the geneticenvironmental structure of RSB in early typical development. [ABSTRACT FROM AUTHOR]

The present study examined sibling influence over reactive and proactive aggression in a sample of 452 same-sex twins (113 male dyads, 113 female dyads). Between and within siblings influence processes were examined as a function of relative levels of parental coercion and hostility to test the hypothesis that aggression contagion between twins occurs only among dyads who experience parental coerciveness. Teacher reports of reactive and proactive aggression were collected for each twin in kindergarten (M = 6.04 years; SD = 0.27) and in first grade (M = 7.08 years; SD = 0.27). Families were divided into relatively low, average, and relatively high parental coercion-hostility groups on the basis of maternal reports collected when the children were 5 years old. In families with relatively high levels of parental coercion-hostility, there was evidence of between-sibling influence, such that one twin's reactive aggression at age 6 predicted increases in the other twin's reactive aggression from ages 6 to 7, and one twin's proactive aggression at age 6 predicted increases in the other twin's proactive aggression from ages 6 to 7. There was also evidence of within-sibling influence such that a child's level of reactive aggression at age 6 predicted increases in the same child's proactive aggression at age 7, regardless of parental coercion-hostility. The findings provide new information about the etiology of reactive and proactive aggression and individual differences in their developmental interplay. [ABSTRACT FROM AUTHOR]

We investigated age and gender effects on 'Positive Orientation' ( POS)-an individual's tendency to view life with a positive outlook-using a genetically informed design. Study subjects were 1016 twins aged 22-75 from the Italian twin registry. We assessed POS by the recently developed P-scale. First, we used confirmatory factor analysis to investigate scale's measurement invariance by age and gender. Then, we applied biometric modelling to estimate genetic and environmental components of POS score. Overall, we found a satisfactory degree of measurement invariance by both age and gender. Results from these analyses further indicated an increasing mean level of POS across the lifespan. Additive genetic and unshared environmental factors explained respectively 58% and 42% of variance in POS score, with no significant gender differences; furthermore, the pattern of change of gene-environment architecture of POS over time was consistent with a greater plasticity of personality at older ages. [ABSTRACT FROM AUTHOR]

Friend support is often assumed to exert direct environmental influences on psychological distress, yet the role of both genetic and environmental influences on this association has not been examined. This study investigates whether both genetic and environmental factors explain the link between friend support and psychological distress in adults. The sample was drawn from the Midlife Development in the United States study and included 947 pairs of monozygotic, same-sex dizygotic (DZ), and opposite-sex DZ twins. Results showed that genetic influences explain the association between friend support and psychological distress, suggesting that heritable contributions to friend support also shape psychological distress. Interventions focused on psychological distress should consider how individuals' heritable characteristics influence their friend support and psychological distress. [ABSTRACT FROM AUTHOR]

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]

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]

This study used the monozygotic (MZ) twin difference method to examine whether differences in friends' aggression increased the differences in MZ twins' aggression and depressive symptoms from kindergarten to Grade 1 and whether perceived victimization by the friend played a mediating role in this context. Participants were 223 MZ twin pairs. Results showed that differences in kindergarten friends' aggression significantly predicted an increased difference in MZ twins' aggression from kindergarten (mean age = 6.7 years) to Grade 1 (mean age = 7.5 years) for both boys and girls. Differences in perceived victimization by the friend mediated this association, albeit only in boys. Differences in perceived victimization by the friend also predicted an increase in MZ twins' differences in depressive symptoms. These results support the importance of friendship experiences during early childhood. [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]

Abstract: Objective: To evaluate the total number of inter-twin contacts between monochorionic diamniotic (MD) and dichorionic diamniotic (DD) twins using four-dimensional (4D) sonography late in the first trimester of pregnancy. Method: Six MD and 8 DD pregnancies were studied for 30minutes with 4D sonography at 10–11 and 12–13weeks of gestation. A total of 10 types of inter-twin contact was evaluated. Results: There was a significant difference in the total number of all contacts between MD and DD twins at the 10–11weeks of gestation (P <0.05). There was also a significant difference in the total number of contacts between 10–11 and 12–13weeks of gestation in DD twins (P <0.05). Conclusion: Four-dimensional sonography provides a means of evaluating inter-twin contact in the first trimester of pregnancy and could be an accurate and reliable tool in studies of inter-twin behavior. [Copyright &y& Elsevier]

We tested the structure and magnitude of genetic and environmental influences on the overlap among self-esteem, negative emotionality, and major depression symptoms in adolescent girls ( N=706) from the Minnesota Twin Family Study. Genetic and environmental influences on all three operated via a general, heritable factor. Genetic influences explained the majority of overlap among the three constructs, as well as most of the variance in self-esteem and negative emotionality. Genetic influences on depression were more modest and largely due to genetic factors specific to depression. These findings support the theory that self-esteem, depression, and neuroticism represent aspects of a common temperamental core. The interrelations among the three constructs in mid-adolescence is consistent with their interrelations in adulthood. [ABSTRACT FROM AUTHOR]

Studies have demonstrated ERP abnormalities related to concentration difficulties in post-traumatic stress disorder (PTSD). We used an identical-twin, case-control design to investigate whether these abnormalities reflect pre-trauma vulnerability or the acquired consequence of PTSD. Vietnam combat veterans and their non-combat-exposed, identical twins completed a three-tone oddball task. Veterans with PTSD had delayed target N2 latencies compared to veterans without PTSD. In a small nonmedicated, nonsmoking subsample, veterans with PTSD also had significantly diminished target P3b amplitudes. A mixed-model, random-effects analysis on the nonmedicated, nonsmoking subsample that included the combat-unexposed co-twins showed a significant Diagnosis × Combat Exposure interaction for target P3b amplitude. Results replicate increased N2 latency and diminished P3b amplitude in PTSD and suggest that diminished P3b amplitude is an acquired condition in PTSD. [ABSTRACT FROM AUTHOR]

Aims To explore the developmental relationships between early-onset depressive disorders and later use of addictive substances. Design, setting and participants A sample of 1545 adolescent twins was drawn from a prospective, longitudinal study of Finnish adolescent twins with baseline assessments at age 14 years and follow-up at age 17.5 years. Measurements At baseline, DSM-IV diagnoses were assessed with a professionally administered adolescent version of Semi-Structured Assessment for Genetics of Alcoholism (C-SSAGA-A). At follow-up, substance use outcomes were assessed via self-reported questionnaire. Findings Early-onset depressive disorders predicted daily smoking [odds ratio (OR) 2.29, 95% confidence interval (CI) 1.49–3.50, P < 0.001], smokeless tobacco use (OR = 2.00, 95% CI 1.32–3.04, P = 0.001), frequent illicit drug use (OR = 4.71, 95% CI 1.95–11.37, P = 0.001), frequent alcohol use (OR = 2.02, 95% CI 1.04–3.92, P = 0.037) and recurrent intoxication (OR = 1.83, 95% CI 1.18–2.85, P = 0.007) 3 years later. ORs remained significant after adjustment for comorbidity and exclusion of baseline users. In within-family analysis of depression-discordant co-twins (analyses that control for shared genetic and familial background factors), early-onset depressive disorders at age 14 predicted significantly frequent use of smokeless tobacco and alcohol at age 17.5. Conclusions Our results suggest important predictive associations between early-onset depressive disorders and addictive substance use, and these associations appear to be independent of shared familial influences. [ABSTRACT FROM AUTHOR]

Monitoring the correspondence between the intended and actually executed action, a fundamental mechanism of behavioral regulation, is reflected by error-related negativity (ERN), an ERP component generated by the anterior cingulate cortex. This study examined genetic influences on the ERN and other components related to action monitoring (correct negativity, CRN, and error positivity, Pe). A flanker task was administered to adolescent twins (age 12) including 99 monozygotic (MZ) and 175 dizygotic (DZ) pairs. Genetic analysis showed substantial heritability of all three ERP components (40%–60%) and significant genetic correlations between them. This study provides the first evidence for heritable individual differences in the neural substrates of action monitoring and suggests that ERN, CRN, and Pe can potentially serve as endophenotypes for genetic studies of personality traits and psychopathology associated with abnormal regulation of behavior. [ABSTRACT FROM AUTHOR]

Background Constructs such as drinking expectancies (beliefs regarding the effects of alcohol) and motives (drinking alcohol to achieve a valued end) have been shown to be associated with various stages of alcohol use behaviors. However, little is known of the extent to which genetic and environmental influences contribute to individual differences in expectancies and motives. Methods Using data from 3656 young adult same-sex female twins, we examined the association between measures of drinking expectancies and motives and drinking behaviors. Using twin models, we estimated the extent to which genetic, shared and non-shared environmental factors influenced individual differences in expectancies and motives and also tested whether the extent of the genetic and environmental contributions on expectancies varied across abstainers and users of alcohol. Results Expectancies predicted initiation of alcohol use. Both motives and expectancies were associated with frequency and quantity of alcohol consumption and drinks-to-intoxication. There was no evidence for heritable influences on expectancies and enhancement motives, with familial similarity for these traits being due to shared environment. Heritable influences on social, coping and conformity motives ranged from 11% to 33%. When expectancies were stratified by alcohol use, significant heritable influences (31–39%) were found for cognitive–behavioral impairment and risk-taking/negative self-perception (RT/NSP) in abstainers only, while environmental influences contributed to familial variance for other measures of expectancies in alcohol users. Conclusions Environmental influences (both familial and individual-specific) shape alcohol expectancies, while heritable influences may predispose to motives for drinking. Individual differences in expectancies are moderated by alcohol use, suggesting that sources of individual differences in expectancies may vary in drinkers versus abstainers. [ABSTRACT FROM AUTHOR]

Objective: To examine whether a high genetic liability to develop affective disorder is associated with specific personality traits. Method: A cross-sectional, high-risk, case–control study. Through nation-wide registers, healthy monozygotic (MZ) and dizygotic (DZ) twins with (high-risk twins) and without (the control group/low-risk twins) a co-twin history of affective disorder were identified. Personality traits were compared for a total of 211 high-risk and low-risk twins. Results: In univariate analyses, the high-risk twins had a higher level of neuroticism than the control twins ( P = 0.03). In multivariate analyses, a high genetic liability to affective disorder was not significantly associated with neuroticism but correlated to sex, minor psychopathology and recent life events. Conclusion: A high genetic liability to affective disorder showed an association with neuroticism, but the association interacts with other predictors of affective disorder such as female gender, minor psychopathology and recent adversity. [ABSTRACT FROM AUTHOR]

Although religiousness is considered a protective factor against antisocial behaviors and a positive influence on prosocial behaviors, it remains unclear whether these associations are primarily genetically or environmentally mediated. In order to investigate this question, religiousness, antisocial behavior, and altruistic behavior were assessed by self-report in a sample of adult male twins (165 MZ and 100 DZ full pairs, mean age of 33 years). Religiousness, both retrospective and current, was shown to be modestly negatively correlated with antisocial behavior and modestly positively correlated with altruistic behavior. Joint biometric analyses of religiousness and antisocial behavior or altruistic behavior were completed. The relationship between religiousness and antisocial behavior was due to both genetic and shared environmental effects. Altruistic behavior also shared most all of its genetic influence, but only half of its shared environmental influence, with religiousness. [ABSTRACT FROM AUTHOR]

Little is known about the underlying causes and developmental patterns of stability and change in early reading abilities. In a longitudinal study of twins (n=4,291 pairs), individual differences in reading achievement assessed by teachers using U.K. National Curriculum (NC) criteria showed substantial heritabilities at ages 7, 9, and 10 years (.57-.67) and modest shared environmental influences (.10-.17). Stability in NC scores was primarily mediated genetically. There was also evidence for age-specific genetic influences at each age. Genetic influences on reading are substantial and stable during the elementary school years despite the shift from "learning to read" to "reading to learn." [ABSTRACT FROM AUTHOR]

Background: A fundamental issue for child psychology concerns the origins of individual differences in early reading development. Method: A measure of word recognition, the Test of Word Reading Efficiency (TOWRE), was administered by telephone to a representative population sample of 3,909 same-sex and opposite-sex pairs of 7-year-old twins. Analyses allowing for sex differences in aetiology were used to estimate the extent to which genetic and environmental influences contribute to normal variation in word recognition and word recognition difficulties, defined by scores below the 5th and 10th percentiles of the unselected sample. Results: Both normal variation in word recognition and impaired word recognition abilities were substantially heritable (h2 = .65–.67; h = .37–.72). Environmental influences were primarily shared between twins, rather than specific to each individual, and small to moderate in magnitude. There was evidence for qualitative sex differences. Quantitative sex differences were also suggested at the extremes, with genetic influences being more important as a cause of reading difficulties in boys than in girls. Conclusions: These findings indicate that early individual differences and impairments in word recognition are principally influenced by genetic factors and may involve partly distinct genetic or environmental effects in boys and girls. Crucially, they also provide evidence that reading impairments are linked genetically to the normal distribution. Genetic risk for early impairments in word recognition is continuous rather than discrete. [ABSTRACT FROM AUTHOR]

Childhood psychopathology is associated with both high and low levels of prosocial behaviour. It has been proposed that the development of prosocial behaviour shows emerging and consolidating individual differences as children grow older. The influences on these individual differences have not previously been examined in children and adolescents using multiple raters in a genetically informative design. Twin data from 682 families based on parent and teacher reports were used to examine the genetic and environmental influences on prosocial behaviour in 5–16-year-olds. Effects of sex, age and rater were examined. There were no significant differences in the magnitude of genetic and environmental influence on male and female prosocial behaviour. Declining common environment and increasing genetic influences were seen with age. This emerged as a trend in parent data and reached statistical significance in teacher data. When parent and teacher data were examined together in a rater bias model significant bias acting on the parent ratings emerged, in keeping with previous discrepancies between parental and observational measures. There was overlap in the phenotype rated by parents and teachers, with a highly heritable common underlying phenotype. The influences on the distribution of prosocial behaviour in children and adolescents show declining shared environmental and increasing genetic influences with age. Parental assessments of prosocial behaviour show significantly higher scores than teacher reports and whilst there is overlap in the phenotype rated by parents and teachers, parents show significant bias in their ratings. [ABSTRACT FROM AUTHOR]

Two studies reported that twins may dispute ownership of autobiographical experiences. One observation made in both studies was that the events that were disputed by the twins were rather ordinary events. In the present study, we tested the idea that the disputed memories are such ordinary and mundane events. A brief narrative description of disputed and nondisputed events that were provided by participants in the Ikier, Tekcan, Gülgöz, and Küntay (2003) study was given to an independent sample of participants who were asked to rate (a) the ordinariness of the event, given the age and sex of the protagonist of the event and (b) the likelihood that the event would have happened to them. Results showed that disputed memories were rated as more mundane than nondisputed personal memories. Moreover, a substantial portion of the disputed memories from the Ikier et al. study were for events that our subjects reported to have also experienced. These findings are discussed in the context of cognitive processes contributing to formation of false memories. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Twin studies of childhood behavior problems support the conclusion that individual differences in impulsivity, hyperactivity, and inattention are largely due to genetic influences. Non-genetic variation is due to environmental influences that are unique to the individual, and possibly to rater contrast effects. In the present longitudinal twin study, we report on the size of genetic and environmental effects on individual differences in attention problems at ages 3, 7, 10 and 12 years. Mothers were asked to complete the CBCL for their twin offspring when the children were 3 ( n = 11,938), 7 ( n = 10,657), 10 ( n = 6,192), and 12 years old ( n = 3,124). We focus on the Overactivity (OA) scale in the Child Behavior Checklist (CBCL/2–3), and on the Attention Problem (AP) scale of the CBCL/4–18. The data were analyzed using longitudinal structural equation modeling. Broad heritability of OA and AP is estimated at nearly 75%, at each age. A contrast effect was observed at age 3 only. The results revealed less stability of OA at age 3 to AP at age 7 ( r = .40), compared to the stability from AP at age 7 and beyond ( r = .70). Genetic effects explained between 76% and 92% of the covariance between OA and AP. OA and AP are highly heritable at all ages in both genders. The same set of genes appears to be expressed in boys and girls. The size of genetic and environmental contributions remains the same across the ages studied. Stability in OA and AP is accounted for by genetic influences. Children who do not display OA or AP at a given age are unlikely to develop these problems at a subsequent age. [ABSTRACT FROM AUTHOR]

Findings from family and twin-based studies of Attention Deficit/Hyperactivity Disorder (ADHD) have indicated that inattentive and combined subtypes cluster together among sibling pairs who both express ADHD symptoms. The current report examines the familial clustering of ADHD subtypes, defined according to latent class and DSM-IV criteria, in a general population sample of 2,848 Australian twins, 1,013 of their non-twin siblings and 4,036 female twins from Missouri, USA. Significant clustering of DSM-IV inattentive and combined subtypes, and significant clustering of the same latent classes among siblings was predicted. Logistic regression was used to assess 1) the clustering of same and different subtype combinations among twin and twin-sibling pairs and 2) whether genetic influences contribute significantly to the observed patterns of subtype combinations among siblings. With the exception of the DSM-IV hyperactive-impulsive subtype and the severe hyperactive-impulsive latent class, all other sibling DSM-IV and latent class ADHD subtypes consistently exhibited significant same-subtype clustering with MZ probands, DZ probands and their siblings in both samples. Furthermore, a significant genetic influence contributing to subtype concordance was detected for every DSM-IV subtype excluding hyperactive-impulsive, and for all eight latent classes. While some instances of significant different-subtype clustering among siblings was observed across both classification systems and samples, the particular subtype combinations involved were largely inconsistent across samples and no significant genetic influences contributing towards these discordant subtype combinations were detected. For both DSM-IV and latent class subtypes, the overall pattern of findings in both samples indicated significant familial clustering of same-subtype combinations and significant genetic influences contributing to these patterns of subtype concordance, despite important sample differences. These findings further extend previous work and are most consistent with the presence of multiple independent forms of ADHD. [ABSTRACT FROM AUTHOR]

In this study several aspects of attention were studied in 237 nearly 6-year-old twin pairs. Specifically, the ability to sustain attention and inhibition were investigated using a computerized test battery (Amsterdam Neuropsychological Tasks). Furthermore, the Teacher's Report Form (TRF) was filled out by the teacher of the child and the attention subscale of this questionnaire was analyzed. The variance in performance on the different tasks of the test battery and the score on the attention scale of the TRF were decomposed into a contribution of the additive effects of many genes (A), environmental effects that are shared by twins (C) and unique environmental influences not shared by twins (E) by using data from MZ and DZ twins. The genetic model fitting results showed an effect of A and E for the attention scale of the TRF, and for some of the inhibition and sustained attention measures. For most of the attention variables, however, it was not possible to decide between a model with A and E or a model with C and E. Time-on-task effects on reaction time or number of errors and the delay after making an error did not show familial resemblances. A remarkable finding was that the heritability of the attention scale of the TRF was found to be higher than the heritability of indices that can be considered to be more direct measures of attention, such as mean tempo in the sustained attention task and response speed in the Go–NoGo task. In preschoolers, familial resemblances on sustained attention and inhibition were observed. [ABSTRACT FROM AUTHOR]

We investigated the aetiology of language impairment in 579 four-year-old twins with low language performance and their co-twins, members of 160 MZ twin pairs, 131 same-sex DZ pairs and 102 opposite-sex DZ pairs. Language impairment in 4-year-olds was defined by scores below the 15th percentile on a general factor derived from an extensive language test battery. Language impairment of different degrees of severity was investigated by using multiple cut-offs below the 15th percentile. DeFries–Fulker extremes analysis indicated that language impairment as measured by the general language scale is under strong genetic influence. In addition, group differences heritability showed an increasing trend (from 38% to 76%) as a function of severity of language impairment. Although more boys are impaired than girls, incorporating opposite-sex DZ pairs into the analysis found neither quantitative nor qualitative differences between boys and girls in genetic and environmental aetiologies. Language impairment at four years is heritable. This finding replicates previous research on language impairment and extends it by showing that language impairment is heritable in twins selected from a representative community sample. Despite the mean difference between boys and girls, genetic and environmental influences are quantitatively and qualitatively similar for language impairment for boys and girls. For both boys and girls, heritability appears to be greater for more severe language impairment, indicating stronger influence of genes at the lower end of language ability. [ABSTRACT FROM AUTHOR]

The relation between sociability and positive affect is one of the most often replicated results of research on personality and subjective well-being. It is shown how behavior genetics can contribute to our understanding of the covariance between sociability and positive emotionality. The results of a multimethod behavior-genetic study with 158 monozygotic and 120 dizygotic twins are reported. In this study, sociability and two components of positive emotionality (positive affect, energy) were assessed by self-report and other report. Additionally, positive state affect was assessed in five situations and aggregated across situations. The results showed that there are strong genetic correlations between all variables. Furthermore, there are substantive correlations between the nonshared environmental components of the different variables. Shared environmental influences, however, seemed to be unimportant for explaining the correlations between sociability and the different components of positive emotionality. The results are discussed with respect to their implications for future research on sociability and positive emotionality. [ABSTRACT FROM AUTHOR]

The mother–infant communicative speech of a group of mothers of 4-month-old first-born twin infants was compared to the speech of a group of mothers of first-born singleton infants. Maternal groups were matched on age, education level, mother–infant attachment status and infant gender, and maternal depression was assessed as a control variable. Maternal speech was coded for focus, content, complexity and syntax of mothers' utterances. The findings of earlier studies with toddler age twins, that maternal speech style was more directive and less infant-focused, were replicated in this prelinguistic period of infancy. Compared to mothers of singletons, mothers of twins used less infant-focused speech, were less responsive to their infants' cues, and attributed less agency to their infants. Mothers of twins also used fewer questions and requests but did not differ from mothers of singletons in their use of negatives and imperatives. These early differences in the language learning environments of twin and singleton infants may be due to the reduced opportunities that mothers of twins have to establish dyadic communicative routines with their infants and to familiarize themselves with their infants as interactive partners, and may have implications for the early language development of twins. Copyright © 2002 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Deals with a study which examined differential heritability of eating disorders in prepubertal and pubertal twins. Methods; Results; Discussion.

Recent studies have demonstrated substantial correlations between normal and abnormal personality traits. Yet little is known about how these correlations are mediated genetically and environmentally: Do normal and abnormal personality traits stem from the same underlying genes and environments? We addressed this question using data from 128 monozygotic and dizygotic twin pairs in the Minnesota Study of Twins Reared Apart (MISTRA). Additive genetic and nonshared environmental correlations between scales of the Minnesota Multiphasic Personality Inventory (MMPI)--an index of abnormal personality--and the Multidimensional Personality Questionnaire (MPQ)--an index of normal personality--were estimated. Results indicated that phenotypic correlations between normal and abnormal personality were mediated by genetic as well as environmental factors, although the magnitude of genetic mediation tended to be larger overall. Moreover, the patterns of phenotypic, genetic, and environmental relationships among the scales were similar, suggesting that influences on normal and abnormal personality act through systems common to both. It is suggested that future research focus on the neurogenetic substrates of these shared systems and how dysfunction in these systems influences development of disordered personality. [ABSTRACT FROM AUTHOR]

The degree to which individual differences in child-parent attachment were mediated by genetic, shared environmental, and nonshared environmental influences was investigated. One hundred and ten preschool-aged twin pairs (N = 220) were assessed in the Strange Situation and coded using conventional four-way classifications and a continuous measure of attachment security. The degree of sibling similarity in attachment was substantial, with an overall concordance rate of 67% at the secure/insecure level. The degree of concordance was equally high in monozygotic and dizygotic twin pairs, 70% and 64%, respectively, suggesting little genetic influence but a moderate degree of discordance. Twin similarity on the continuous measure of attachment security was r(57) = .48 and r(53) = .38 for monozygotic and dizygotic twin pairs, respectively, also consistent with a modest role for genetic influence but a significant effect for shared and nonshared environment. The implications for genetic influences on the environment and for understanding nonshared and shared environmental influences are discussed. [ABSTRACT FROM AUTHOR]

Differences in mothers' parenting behaviors toward their identical twin preschoolers were examined to identify nonshared environmental processes in social-emotional development. The study included 62 pairs of 3&half;-year-old same-sex identical twins. Indicators of each child's social-emotional development (temperament, prosocial behavior, behavior problems and noncompliance) and parenting environment (warmth and negativity, positive and negative control, responsiveness) were assessed using observers', interviewers', and parents' ratings. Mothers treated their identical twins differently, and this differential treatment covaried in expected ways with identical twin differences in social-emotional adjustment. The twin who received more supportive and less punitive forms of parenting was also higher in positive mood and prosocial behaviors and lower in negative mood and behavior problems when compared to her or his twin. [ABSTRACT FROM AUTHOR]

Despite cognitive neuroscience's emphasis on the modularity of cognitive processes, multivariate genetic research indicates that the same genetic factors largely affect diverse cognitive abilities, at least from middle childhood onward. We explored this issue for verbal and nonverbal cognitive development in infancy in a study of 1,937 pairs of same-sex 2-year-old twins born in England and Wales in 1994. The twins were assessed by having their parents use a measure of productive vocabulary (the MacArthur Communicative Development Inventory) and a novel measure of nonverbal cognitive abilities (Parent Report of Children's Ability). Verbal and nonverbal development correlated .42. A multivariate genetic analysis indicated that genetic factors were responsible for less than half of this phenotypic correlation. Moreover, the genetic correlation between verbal and nonverbal abilities was only .30, which indicates that genetic effects on verbal and nonverbal abilities are largely independent in infancy. These multivariate genetic results suggest that genetic effects on cognitive abilities are modular early in development and then become increasingly molar. The implications of this result for theories of cognitive development are discussed. [ABSTRACT FROM AUTHOR]

Examines sex differences in verbal and nonverbal cognitive development of twins. Comparison between the scores of both measures in girls and boys; Demonstration of greater heritability of boys in verbal measure; Influence of sex-specific factors on individual differences in verbal ability; Similarity of influences for both sexes in nonverbal development.

Analyzing data from Loehlin and Nichols's (1976) classic twin study, we computed measures of Masculine Instrumentality (M), Feminine Expressiveness (F), and Gender Diagnosticity (GD). Quantitative genetic modeling analyses of within-sex individual differences in M, F, and GD indicated that: (1) Additive genetic factors contribute significantly to individual differences in M, F, and GD. (2) The environmental effects on M, F, and GD tend to be nonshared. (3) The genetic and environmental components of individual differences in M, F, and GD tend not to show gender differences. Finally, (4) the estimated within-sex heritability of GD (.53) is significantly greater than the estimated within-sex heritabilities of either M (.36) or F (.38). [ABSTRACT FROM AUTHOR]

Studies the extent to which heredity influences perceptions of childhood family environment in adult twins who were reared apart. Effect on self-reports of childhood family environment; Importance of environmental influences; Personality traits; Cultural orientation.

Presents a comparative analysis of the mental ability profiles of monozygotic (MZ) and dizygotic (DZ) twins. Concordance of MZ twins relative to DZ twins; Application of the Wechsler Intelligence Scale to twins; Profiles of MZ and DZ twins under the Bayley scales.