Genetics and developmental psychopathology: 2. The main effects of genes and environment on behavioral problems in the Virginia Twin Study of Adolescent Behavioral Development

Parental criticism is an environmental influence on adolescent somatic symptoms

Previous studies have suggested that parental criticism leads to more somatic symptoms in adolescent children. However, this research has not assessed the direction of causation or whether genetic and/or environmental influences explain the association between parental criticism and adolescent somatic symptoms. As such, it is impossible to understand the mechanisms that underlie this association. The current study uses the Extended Children of Twins design to examine whether parents' genes, adolescents' genes, and/or environmental factors explain the relationship between parental criticism and adolescent somatic symptoms. Participants came from 2 twin samples, including the Twin and Offspring Study in Sweden (N = 868 pairs of adult twins and each twin's adolescent child) and from the Twin Study of Child and Adolescent Development (N = 690 pairs of twin children and their parents). Findings showed that environmental influences account for the association between parental criticism and adolescent somatic symptoms. This suggests that parents' critical behaviors exert a direct environmental effect on somatic symptoms in adolescent children. Results support the use of intervention programs focused on parental criticism to help reduce adolescents' somatic symptoms.

Shared genetic and environmental influences on early temperament and preschool psychiatric disorders in Hispanic twins

OBJECTIVE

Despite an increasing recognition that psychiatric disorders can be diagnosed as early as preschool, little is known how early genetic and environmental risk factors contribute to the development of psychiatric disorders during this very early period of development.

METHOD

We assessed infant temperament at age 1, and attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and separation anxiety disorder (SAD) at ages 3 through 5 years in a sample of Hispanic twins. Genetic, shared, and non-shared environmental effects were estimated for each temperamental construct and psychiatric disorder using the statistical program MX. Multivariate genetic models were fitted to determine whether the same or different sets of genes and environments account for the co-occurrence between early temperament and preschool psychiatric disorders.

RESULTS

Additive genetic factors accounted for 61% of the variance in ADHD, 21% in ODD, and 28% in SAD. Shared environmental factors accounted for 34% of the variance in ODD and 15% of SAD. The genetic influence on difficult temperament was significantly associated with preschool ADHD, SAD, and ODD. The association between ODD and SAD was due to both genetic and family environmental factors. The temperamental trait of resistance to control was entirely accounted for by the shared family environment.

CONCLUSIONS

There are different genetic and family environmental pathways between infant temperament and psychiatric diagnoses in this sample of Puerto Rican preschool age children.

Sex Differences in Genetic and Environmental Influences on Adolescent Depressive Symptoms: A Meta-Analytic Review

Although sex difference in the mean level of depressive symptoms has been well established, the sex difference in genetic and environmental influences on adolescent depressive symptoms is unclear. The current study conducted a meta-analysis of twin studies on sex differences in self- and parent-reported adolescent depressive symptoms. For self-reports, genetic factors influenced adolescent depressive symptoms equally for boys and girls, accounting for 46% of variation, but shared environmental factors had stronger impacts on adolescent girls' versus boys' depressive symptoms (13% versus 1% of the variance). For parent-reports, genetic, shared, and nonshared environmental factors influenced adolescent depressive symptoms equally, with separate estimates of 34%, 35%, and 31%. The implications of sex difference in genetic and environmental etiologies of depressive symptoms are discussed.

Epidemiology of child psychopathology: major milestones

Child psychiatric epidemiology has developed rapidly from descriptive, cross-sectional studies in the 1960s to the current large-scale prospective cohorts that unravel aetiological mechanisms. The objective of the study was to give an overview of epidemiological studies that have influenced child psychiatry. A chronological overview of selected major milestone studies was obtained to demonstrate the development of child psychiatric epidemiology, with a more in-depth discussion of findings and methodological issues exemplified in one cohort, the Generation R Study. Epidemiological studies have been successful in describing the frequency and course of child psychiatric problems. The high expectations that biological factors can be used to better explain, diagnose or predict child psychiatric problems have not been met. More ambitious large-scale child psychiatric cohort studies are needed, carefully applying genetics, neuroscience or other molecular research to better understand how the brain produces maladaptive behaviour. Progress will only be attained if the basic sciences are systematically integrated in cohorts with rigorous epidemiological designs rather than hurriedly inserted in child psychiatric studies.

The heritability of insomnia progression during childhood/adolescence: results from a longitudinal twin study

STUDY OBJECTIVES

To determine prevalence and heritability of insomnia during middle/late childhood and adolescence; examine longitudinal associations in insomnia over time; and assess the extent to which genetic and environmental factors on insomnia remain stable, or whether new factors come into play, across this developmental period.

DESIGN

Longitudinal twin study.

SETTING

Academic medical center.

PATIENTS OR PARTICIPANTS

There were 739 complete monozygotic twin pairs (52%) and 672 complete dizygotic twin pairs (48%) initially enrolled and were followed up at three additional time points (waves). Mode ages at each wave were 8, 10, 14, and 15 y (ages ranged from 8-18 y).

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Clinical ratings of insomnia symptoms were assessed using the Child and Adolescent Psychiatric Assessment (CAPA) by trained clinicians, and rated according to Diagnostic and Statistical Manual of Mental Disorders (DSM)-III-R criteria for presence of 'clinically significant insomnia', over four sequential waves. Insomnia symptoms were prevalent but significantly decreased across the four waves (ranging from 16.6% to 31.2%). 'Clinically significant insomnia' was moderately heritable at all waves (h² range = 14% to 38%), and the remaining source of variance was the nonshared environment. Multivariate models indicated that genetic influences at wave 1 contributed to insomnia at all subsequent waves, and that new genetic influences came into play at wave 2, which further contributed to stability of symptoms. Nonshared environmental influences were time-specific.

CONCLUSION

Insomnia is prevalent in childhood and adolescence, and is moderately heritable. The progression of insomnia across this developmental time period is influenced by stable as well as new genetic factors that come into play at wave 2 (modal age 10 y). Molecular genetic studies should now identify genes related to insomnia progression during childhood and adolescence.

Higher prevalence of iron deficiency as strong predictor of attention deficit hyperactivity disorder in children

Background:

It has been reported that ferritin and iron deficiency may be related to the path physiology of attention deficit hyperactivity disorder (ADHD).

Aim:

The aim of this study was to determine the association between iron deficiency and ADHD and the impact and role of iron deficiency on the development of ADHD in children.

Subjects and Methods:

The study based on the case-control study age- and sex-matched control and conducted at the School Health and Primary Healthcare Clinics, Qatar. A total of 630 children with ADHD aged 5-18 and 630 controls aged 5-18 years old. Sociodemographic and clinical data were collected, including physician diagnosis. The health status of the subjects was assessed by ascertaining clinical presentations and symptoms, family history, body mass index (BMI), iron deficiency, ferritin, serum 25-hydroxyvitamin D, calcium, magnesium, and phosphorus levels. Descriptive, univariate, and multivariate statistical analysis were performed.

Results:

Mean age (standard deviation [SD] in years) for ADHD and control children were 11.54 (3.83) versus 11.50 (3.62). There were statistically significant differences between ADHD versus control children for vitamin D [16.81 (7.84) vs. 22.18 (9.00) ng/ml], serum iron [82.11 (13.61) vs. 85.60 (12.47) ng/ml], ferritin [36.26 (5.93) vs. 38.19 (5.61) ng/ml], hemoglobin [12.02 (2.13) vs. 12.89 (2.02) g/dL], magnesium [0.82 (0.08) vs. 0.88 (0.06) mmol/L], serum calcium level [2.35 (0.12) vs. 2.39 (0.14) mmol/L], and phosphorous [1.47 (0.30) vs. 1.54 (0.26) mmol/L]. Of total 630 of ADHD children, 116 (18.4%) had severe vitamin D deficiency (<10 ng/ml). Multivariate logistic regression analysis revealed that serum vitamin D level, serum iron, ferritin, serum calcium level, physical activity, nervous behavior, consanguinity, BMI, and child order were considered as the main factors associated with the ADHD after adjusting for age, gender, and other variables.

Conclusion:

The study indicates that low serum iron, ferritin levels, and vitamin D deficiency may be associated with ADHD.

Maternal pre-pregnancy weight and externalising behaviour problems in preschool children: a UK-based twin study

OBJECTIVE

To estimate the heritability of child behaviour problems and investigate the association between maternal pre-pregnancy overweight and child behaviour problems in a genetically sensitive design.

DESIGN

Observational cross-sectional study.

SETTING

The Twins and Multiple Births Association Heritability Study (TAMBAHS) is an online UK-wide volunteer-based study investigating the development of twins from birth until 5 years of age.

PARTICIPANTS

A total of 443 (16% of the initial registered members) mothers answered questions on pre-pregnancy weight and their twins' internalising and externalising problems using the Child Behavior Checklist and correcting for important covariates including gestational age, twins' birth weight, age and sex, mother's educational level and smoking (before, during and after pregnancy).

PRIMARY OUTCOMES

The heritability of behaviour problems and their association with maternal pre-pregnancy weight.

RESULTS

The genetic analysis suggested that genetic and common environmental factors account for most of the variation in externalising disorders (an ACE model was the most parsimonious with genetic factors (A) explaining 46% (95% CI 33% to 60%) of the variance, common environment (C) explaining 42% (95% CI 27% to 54%) and non-shared environmental factors (E) explaining 13% (95% CI 10% to 16%) of the variance. For internalising problems, a CE model was the most parsimonious model with the common environment explaining 51% (95% CI 44% to 58%) of the variance and non-shared environment explaining 49% (95% CI 42% to 56%) of the variance. Moreover, the regression analysis results suggested that children of overweight mothers showed a trend (OR=1.10, 95% CI 0.58% to 2.06) towards being more aggressive and exhibit externalising behaviours compared to children of normal weight mothers.

CONCLUSIONS

Maternal pre-pregnancy weight may play a role in children's aggressive behaviour.

Genetic and environmental contributions to social anxiety across different ages: a meta-analytic approach to twin data

Social anxiety disorder (SAD) and social anxiety symptoms (SAS) have been largely studied both epidemiologically and genetically, however, estimates of genetic and environmental influences for these phenotypes widely vary across reports. Based upon available literature, 13 cohorts (42,585 subjects) were included in 3 meta-analytic estimates of the standardized variance components of aetiological influences on SAD/SAS, on the effect of age and of phenotype (symptoms vs. diagnosis). The proportions of variance accounted for by genetic and environmental factors were calculated by averaging estimates among studies, and pondered by the number of individuals in each sample. Meta-analytic estimations showed that genetic and non-shared environmental factors explain most of individual differences for SAD/SAS. In adults, the genetic contribution was half than that in younger patients, with higher contribution of non-shared environmental influences. In contrast, the shared environmental factors seem to be less relevant.

Attention-deficit/hyperactivity disorder polygenic risk scores predict attention problems in a population-based sample of children

OBJECTIVE

Clinically, attention-deficit/hyperactivity disorder (ADHD) is characterized by hyperactivity, impulsivity, and inattention and is among the most common childhood disorders. These same traits that define ADHD are variable in the general population, and the clinical diagnosis may represent the extreme end of a continuous distribution of inattentive and hyperactive behaviors. This hypothesis can be tested by assessing the predictive value of polygenic risk scores derived from a discovery sample of ADHD patients in a target sample from the general population with continuous scores of inattention and hyperactivity. In addition, the genetic overlap between ADHD and continuous ADHD scores can be tested across rater and age.

METHOD

The Psychiatric Genomics Consortium has performed the largest genome-wide analysis (GWA) study of ADHD so far, including 5,621 clinical patients and 13,589 controls. The effects sizes of single nucleotide polymorphisms (SNPs) estimated in this meta-analysis were used to obtain individual polygenic risk scores in an independent population-based cohort of 2,437 children from the Netherlands Twin Register. The variance explained in Attention Problems (AP) scale scores by the polygenic risk scores was estimated by linear mixed modeling.

RESULTS

The ADHD polygenic risk scores significantly predicted both parent and teacher ratings of AP in preschool- and school-aged children.

CONCLUSION

These results indicate genetic overlap between a diagnosis of ADHD and AP scale scores across raters and age groups and provides evidence for a dimensional model of ADHD. Future GWA studies on ADHD can likely benefit from the inclusion of population-based cohorts and the analysis of continuous scores.

Toward a Bioecological Model of School Engagement: A Biometric Analysis of Gene and Environmental Factors

School disengagement is associated with poor academic achievement, dropout, and risk behaviors such as truancy, delinquency, and substance use. Despite empirical research identifying risk correlates of school disengagement across the ecology, it is unclear from which domain these correlates arise. To redress this issue, the current study used intraclass correlation and DeFries-Fulker analyses to longitudinally decompose variance in three domains of engagement (academic, behavioral, and emotional) using data from the National Longitudinal Study of Adolescent Health. Findings suggest that nonshared environmental factors (that is, environmental contexts and experiences that are unique to each sibling) account for approximately half of the variance in indicators of school disengagement when controlling for genetic influences, and that this variance increases as adolescents grow older and rely less on their immediate family. The present study contributes new evidence on the biosocial underpinnings of school engagement and highlights the importance of interventions targeting factors in the nonshared environment.

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

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

Assessing genetic influences on behavior: informant and context dependency as illustrated by the analysis of attention problems

Assessment of genetic influences on behavior depends on context, informants, and study design: We show (analytically) that, conditional on study design, informant specific genetic variance is included in the genetic variance component or in the environmental variance component. To aid the explanation, we present an illustrative empirical analysis of data from the Netherlands Twin Register. Subjects included 1,571 monozygotic and 2,672 dizygotic 12-year-old twin pairs whose attention problems (AP) were rated by their parents, teachers, and themselves. Heritability estimates (h(2)) of AP were about ~0.75 for same informant ratings (mother, father, and same teacher ratings) and ~0.54 for different informants' ratings (different parents', different teachers', and two twins' self-ratings). Awareness of assessment effects is relevant to research into psychiatric disorders. Differences in assessment can account for age effects, such as a drop in heritability of ADHD symptoms. In genome-wide association studies, effects of rating specific genetic influences will be undetectable.

Genetic and environmental causes of variation in adolescent anxiety symptoms: a multiple-rater twin study

Heritability estimates for adolescent anxiety vary across studies, partly depending on who is rating the symptoms. The goal of our study was to estimate genetic and environmental influences using a multi-informant design with responses from a population-based sample of adolescent twins, their mothers and their fathers (N=1394 families). Results from multivariate biometrical modeling indicated quantitative, but no qualitative sex differences in etiology. The best fitting model was an AE Common Pathway model, defining anxiety as a latent factor common to all informants. This model offers error free estimates of genetic and environmental influences explaining the latent factor variance. Variation in the latent factor was highly genetic, with heritability estimates of 65% for boys and 74% for girls. Non-shared environmental effects explained the remaining variance. In addition, there were significant rater-specific genetic and environmental effects for both sexes. The observed rater differences underline the importance of using several informants when studying adolescent anxiety.

The associations between ADHD and asthma in Korean children

BACKGROUND

The aim of this study was to investigate the associations between attention deficit hyperactivity disorder (ADHD), the most common neuropsychiatric disorder in school children, and childhood allergic disease by evaluating their respective prevalence.

METHODS

Subjects were comprised of first and second grade students in twenty two elementary schools in a city in the Republic of Korea. The mode of measurement for ADHD was based on DSM-IV from clinical interviews conducted by child psychiatrists. Along with the diagnostic interviews, we also used the epidemiological questionnaires, Computerized Attention Deficit-Hyperactivity Disorder Diagnostic System, the abbreviated Conner's Parent Rating Scale (CPRS), and DuPaul's ADHD Rating Scales. Allergic conditions, such as asthma, have been separately evaluated based on the questionnaire items whose validity and reliability were proved by the International Study of Asthma and Allergies in Children (ISAAC). All questionnaires were completed by the subjects' parents.

RESULTS

The lifetime prevalence rate of asthma in ADHD patients was 36.6%, compared to a prevalence of 24.3% in control subjects. The lifetime prevalence rate of allergic rhinitis in ADHD patients was 59.0%, compared to a prevalence of 47.0% in control subjects. Statistically significant difference has been found between the two groups. In the logistic regression model of the ADHD and the control group, the relative risk of asthma was 1.60 times higher (confidence interval 1.301-1.964), the relative risk of allergic rhinitis was 1.38 times higher (confidence interval 1.124-1.681), which showed statistical significance.

CONCLUSIONS

The findings of this study suggest significant association between ADHD and childhood asthma and allergic rhinitis. Therefore, appropriate evaluation and treatment are needed for asthmatic children with attention-deficit symptoms, or allergic rhinitis with ADHD. Besides, further research is needed to determine the etiological approach towards ADHD, asthma, and allergic rhinitis.

Latent classiness and other mixtures

The aim of this article is to laud Lindon Eaves' role in the development of mixture modeling in genetic studies. The specification of models for mixture distributions was very much in its infancy when Professor Eaves implemented it in his own FORTRAN programs, and extended it to data collected from relatives such as twins. It was his collaboration with the author of this article which led to the first implementation of mixture distribution modeling in a general-purpose structural equation modeling program, Mx, resulting in a 1996 article on linkage analysis in Behavior Genetics. Today, the popularity of these methods continues to grow, encompassing methods for genetic association, latent class analysis, growth curve mixture modeling, factor mixture modeling, regime switching, marginal maximum likelihood, genotype by environment interaction, variance component twin modeling in the absence of zygosity information, and many others. This primarily historical article concludes with some consideration of some possible future developments.

Gene × environment effects of serotonin transporter, dopamine receptor D4, and monoamine oxidase A genes with contextual and parenting risk factors on symptoms of oppositional defiant disorder, anxiety, and depression in a community sample of 4-year-old children

Genetic factors can play a key role in the multiple level of analyses approach to understanding the development of child psychopathology. The present study examined gene-environment correlations and gene × environment interactions for polymorphisms of three target genes, the serotonin transporter gene, the D4 dopamine receptor gene, and the monoamine oxidase A gene in relation to symptoms of anxiety, depression, and oppositional behavior. Saliva samples were collected from 175 non-Hispanic White, 4-year-old children. Psychosocial risk factors included socioeconomic status, life stress, caretaker depression, parental support, hostility, and scaffolding skills. In comparison with the short forms (s/s, s/l) of the serotonin transporter linked polymorphic repeat, the long form (l/l) was associated with greater increases in symptoms of oppositional defiant disorder in interaction with family stress and with greater increases in symptoms of child depression and anxiety in interaction with caretaker depression, family conflict, and socioeconomic status. In boys, low-activity monoamine oxidase A gene was associated with increases in child anxiety and depression in interaction with caretaker depression, hostility, family conflict, and family stress. The results highlight the important of gene-environment interplay in the development of symptoms of child psychopathology in young children.

Genetic and environmental influences on depressive symptoms in Chinese adolescents

Adolescent depression is common and has become a major public health concern in China, yet little research has examined the etiology of depression in Chinese adolescents. In the present study, genetic and environmental influences on Chinese adolescent depressive symptoms were investigated in 1,181 twin pairs residing in Beijing, China (ages 11-19 years). Child- and parent-versions of the children's depression inventory were used to measure adolescents' depressive symptoms. For self-reports, genetic factors, shared environmental factors, and non-shared environmental factors accounted for 50, 5, and 45 % of the variation in depressive symptoms, respectively; for parent-reports, genetic factors, shared environmental factors, and non-shared environmental factors accounted for 51, 18, and 31 % of the variation, respectively. These estimates are generally consistent with previous findings in Western adolescents, supporting the cross-cultural generalizability of etiological model of adolescent depression. Neither qualitative nor quantitative sex differences were found in the etiological model. Future studies are needed to investigate how genes and environments work together (gene-environment interaction, gene-environment correlation) to influence depression in Chinese adolescents.

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

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

Four factors for the initiation of substance use by young adulthood: a 10-year follow-up twin and sibling study of marital conflict, monitoring, siblings, and peers

This study examined genetic and environmental influences on associations among marital conflict about the child, parental monitoring, sibling relationship negativity, and peer delinquency during adolescence and initiation of illegal drug use by young adulthood. The sample comprised data collected longitudinally from same-sex sibling pairs and parents when the siblings were 10-18 years old (M = 14.5 and 12.9 years for Child 1 and Child 2, respectively) and 20-35 years old (M = 26.8 and 25.5 years for Child 1 and Child 2, respectively). Findings indicate four factors that explain the initiation of illegal drug use: two shaped by genetic influences and two shaped by environments shared by siblings. The two genetically shaped factors probably have distinct mechanisms: one a child-initiated coercive process in the family and the other parent and peer processes shaped by the child's disclosure. The environmentally influenced factors seem distinctively shaped by poor parental monitoring of both sibs and the effects of siblings on each other's deviancy.

Associations between adolescent depression and parental mental health, before and after treatment of adolescent depression

The negative impacts of parental mental health problems on children and adolescents are well known, but the relationship between a child's depression and their parents' health is not so well understood. Being a carer/parent of someone with mental illness can be associated with negative outcomes for the caregiver. This paper reports the associations between the mental health of adolescents with major depression and their parents, before and after treatment of the adolescent's depression. Data were collected as part of the Adolescent Depression Antidepressants and Psychotherapy Trial, a randomised controlled trial of selective serotonin reuptake inhibitors with and without cognitive behaviour therapy in 208 clinic-recruited adolescents with major depression. The baseline severity of depression in the adolescent was significantly associated with both maternal and paternal mental health (as rated by the General Health Questionnaire). This effect was not confounded by other psychiatric symptoms. The degree of improvement in parental and child mental health was positively correlated across time. Our results support the hypothesis that there is a significant association between parental mental health and adolescent depressive symptoms. This study was not able to establish the direction of this association. In clinical practice, the findings demonstrate the importance of considering the mental health of the parents when treating depressed adolescents.

Sex differences in genetic architecture of complex phenotypes?

We examined sex differences in familial resemblance for a broad range of behavioral, psychiatric and health related phenotypes (122 complex traits) in children and adults. There is a renewed interest in the importance of genotype by sex interaction in, for example, genome-wide association (GWA) studies of complex phenotypes. If different genes play a role across sex, GWA studies should consider the effect of genetic variants separately in men and women, which affects statistical power. Twin and family studies offer an opportunity to compare resemblance between opposite-sex family members to the resemblance between same-sex relatives, thereby presenting a test of quantitative and qualitative sex differences in the genetic architecture of complex traits. We analyzed data on lifestyle, personality, psychiatric disorder, health, growth, development and metabolic traits in dizygotic (DZ) same-sex and opposite-sex twins, as these siblings are perfectly matched for age and prenatal exposures. Sample size varied from slightly over 300 subjects for measures of brain function such as EEG power to over 30,000 subjects for childhood psychopathology and birth weight. For most phenotypes, sample sizes were large, with an average sample size of 9027 individuals. By testing whether the resemblance in DZ opposite-sex pairs is the same as in DZ same-sex pairs, we obtain evidence for genetic qualitative sex-differences in the genetic architecture of complex traits for 4% of phenotypes. We conclude that for most traits that were examined, the current evidence is that same the genes are operating in men and women.

The Beijing Twin Study (BeTwiSt): a longitudinal study of child and adolescent development

Rates of emotional and behavioral problems among children and adolescents in China are increasing and represent a major public health concern. To investigate the etiology of such problems, including the effects and interplay of genes and environment, the Beijing Twin Study (BeTwiSt) was established. A representative sample of adolescent twins in Beijing (N = 1,387 pairs of adolescent twins, mostly between the ages of 10 and 18 years) was recruited and assessed longitudinally. Data collection included the following: emotional and behavioral problems (e.g., depressive symptoms, anxiety, delinquency, drinking, and smoking); family, peer, and school environments; stress; social and academic competence; cognitive traits (e.g., emotion suppression, rumination, and effortful control); and saliva samples for DNA genotyping and sequencing. The combination of quantitative and molecular genetic approaches and the timeliness of the project, with the sample residing in a region with a rapidly changing economic and cultural climate, are particular strengths of this study. Findings from this study are expected to help understanding of the etiological mechanisms underlying child and adolescent normal and abnormal development in regions undergoing substantial social, cultural, and economic changes.

Genetic and environmental contributions to separation anxiety: a meta-analytic approach to twin data

BACKGROUND

Separation anxiety disorder (SAD) and separation anxiety symptoms (SA) have been studied both epidemiologically and genetically; however, large between-studies discrepancies emerge relative to the role of genetic, shared-, and nonshared environmental influences on these conditions.

METHODS

Based upon available literature, 18 cohorts and 31,859 subjects belonging to twin samples in Europe, the United States, and Australia were included in three meta-analytic estimations of: the standardized variance components of etiological influences on SAD/SA, and on the effect of sex and rater.

RESULTS

Meta-analytic estimations carried out on all cohorts showed that within-family (genetic 43% and shared environmental 17%) factors explain most of individual differences for SAD/SA. Meta-heritability estimates were higher among females (.52) than males (.26), whereas nonshared environmental effects were stronger for the latter (.74) than for the former (.41). When SAD/SA was rated by parents, the shared environmental influences were higher than those obtained with self-assessment instruments (.23 versus .05), but this may reflect an age difference between subsamples.

CONCLUSIONS

A shared environmental effect is present and important in SAD/SA. Our results support at an etiological level the involvement of parents in treating SAD/SA in children, and the provision of specific strategies to parents to manage their own anxiety.

Suicidal ideation, depression, and conduct disorder in a sample of adolescent and young adult twins

The co-occurrence of suicidal ideation, depression, and conduct disturbance is likely explained in part by correlated genetic and environmental risk factors. Little is known about the specific nature of these associations. Structured interviews on 2,814 twins from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) and Young Adult Follow-Up (YAFU) yielded data on symptoms of depression, conduct disorder, and adolescent and young adult suicidal ideation. Univariate analyses revealed that the familial aggregation for each trait was explained by a combination of additive genetic and shared environmental effects. Suicidal ideation in adolescence was explained in part by genetic influences, but predominantly accounted for by environmental factors. A mixture of genetic and shared environmental influences explained ideation occurring in young adulthood. Multivariate analyses revealed that there are genetic and shared environmental effects common to suicidal ideation, depression, and conduct disorder. The association between adolescent suicidal ideation and CD was attributable to the same genetic and environmental risk factors for depression. These findings underscore that prevention and intervention strategies should reflect the different underlying mechanisms involving depression and conduct disorder to assist in identifying adolescents at suicidal risk.

Unraveling the effect of genes and environment in the transmission of parental antisocial behavior to children's conduct disturbance, depression and hyperactivity

BACKGROUND

  A critical issue in devising effective interventions for the treatment of children's behavioral and emotional problems identifying genuine family environmental factors that place children at risk. In most twin and family studies, environmental factors are confounded with both direct genetic risk from parents and the indirect effect of genes influencing parents' ability to provide an optimal rearing environment. The present study was undertaken to determine whether parental psychopathology, specifically parental antisocial behavior (ASP), is a genuine environmental risk factor for juvenile conduct disturbance, depression and hyperactivity, or whether the association between parental ASP and children's behavioral and emotional problems can be explained as a secondary consequence of the intergenerational transmission of genetic factors.

METHODS

  An extended children of twins design comprised of data collected on 2,674 adult female and male twins, their spouses, and 2,454 of their children was used to test whether genetic and/or family environmental factors best accounted for the association between parental antisocial behavior and children's behavioral problems. An age-matched sample of 2,826 juvenile twin pairs from the Virginia Twin Study of Adolescent Behavioral Development was also included to examine developmental differences in gene expression by partitioning child-specific transmissible effects from those effects that persist into adulthood. The fit of alternative models was evaluated using the statistical program Mx.

RESULTS

  We found distinct patterns of transmission between parental antisocial behavior and juvenile conduct, depression and hyperactivity. Genetic and family environmental factors accounted for the resemblance between parents' ASP and children's conduct disturbance. Family environmental factors alone explained the association between child depression and parental ASP, and the impact of parental ASP on hyperactivity was entirely genetic.

CONCLUSIONS

  These findings underscore differences in the contribution of genetic and environmental factors on the patterns of association between parental antisocial behavior and juvenile psychopathology, having important clinical implications for the prevention and amelioration of child behavioral and emotional problems.

Childhood separation anxiety disorder and adult onset panic attacks share a common genetic diathesis

BACKGROUND

Childhood separation anxiety disorder (SAD) is hypothesized to share etiologic roots with panic disorder. The aim of this study was to estimate the genetic and environmental sources of covariance between childhood SAD and adult onset panic attacks (AOPA), with the primary goal to determine whether these two phenotypes share a common genetic diathesis.

METHODS

Participants included parents and their monozygotic or dizygotic twins (n = 1,437 twin pairs) participating in the Virginia Twin Study of Adolescent Behavioral Development and those twins who later completed the Young Adult Follow-Up (YAFU). The Child and Adolescent Psychiatric Assessment was completed at three waves during childhood/adolescence followed by the Structured Clinical Interview for DSM-III-R at the YAFU. Two separate, bivariate Cholesky models were fit to childhood diagnoses of SAD and overanxious disorder (OAD), respectively, and their relation with AOPA; a trivariate Cholesky model also examined the collective influence of childhood SAD and OAD on AOPA.

RESULTS

In the best-fitting bivariate model, the covariation between SAD and AOPA was accounted for by genetic and unique environmental factors only, with the genetic factor associated with childhood SAD explaining significant variance in AOPA. Environmental risk factors were not significantly shared between SAD and AOPA. By contrast, the genetic factor associated with childhood OAD did not contribute significantly to AOPA. Results of the trivariate Cholesky reaffirmed outcomes of bivariate models.

CONCLUSIONS

These data indicate that childhood SAD and AOPA share a common genetic diathesis that is not observed for childhood OAD, strongly supporting the hypothesis of a specific genetic etiologic link between the two phenotypes.

Adolescent religiousness and its influence on substance use: preliminary findings from the Mid-Atlantic School Age Twin Study

Research has consistently shown that religiousness is associated with lower levels of alcohol and drug use, but little is known about the nature of adolescent religiousness or the mechanisms through which it influences problem behavior in this age group. This paper presents preliminary results from the Mid-Atlantic School Age Twin Study, a prospective, population-based study of 6–18-year-old twins and their mothers. Factor analysis of a scale developed to characterize adolescent religiousness, the Religious Attitudes and Practices Inventory (RAPI), revealed three factors: theism, religious/spiritual practices, and peer religiousness. Twin correlations and univariate behavior-genetic models for these factors and a measure of belief that drug use is sinful reveal in 357 twin pairs that common environmental factors significantly influence these traits, but a minor influence of genetic factors could not be discounted. Correlations between the multiple factors of adolescent religiousness and substance use, comorbid problem behavior, mood disorders, and selected risk factors for substance involvement are also presented. Structural equation modeling illustrates that specific religious beliefs about the sinfulness of drugs and level of peer religiousness mediate the relationship between theistic beliefs and religious/spiritual practices on substance use. Limitations and future analyses are discussed.

Can Genetic Factors Explain the Spillover of Warmth and Negativity Across Family Relationships?

Previous studies indicate that the emotional quality of marital relationships is mirrored in parent–child relationships. We explored the degree to which these associations are explained by genetic and environmental factors. Participants were drawn from the Twin and Offspring Study in Sweden (TOSS), and included 544 female twin pairs (258 monozygotic [MZ], 286 dizygotic [DZ]), and 311 male twin pairs (128 MZ, 183 DZ). The spouses and one adolescent child of each twin also participated in this study. The twins completed self-report measures that assessed their marital quality and their warmth and negativity towards their children. Observational ratings of marital warmth and negativity, and of maternal warmth and negativity were obtained for a subset of female twin pairs (150 MZ, 176 DZ). Selfreported marital satisfaction was associated with self-reported parental warmth and negativity for mothers (rs = .25, -.36) and fathers (rs = .25, -.44). For the observational measures, marital warmth was associated with maternal warmth (r = .42), while marital negativity was associated with maternal negativity (r = .34). On average genetic factors explained nearly half of the covariance between selfreported marital satisfaction and parenting for mothers (48%) and fathers (47%). Genetic factors explained 21% of the covariance between observed marital and maternal warmth, but did not contribute to associations between marital and maternal negativity. These findings indicate that parents' genetically influenced characteristics help shape the emotional climate of the family.

Efficacy of Retrospective Recall of Attention-Deficit Hyperactivity Disorder Symptoms: A Twin Study

Attention-deficit hyperactivity disorder (ADHD) is currently recognized as a neurobiological, genetically based disorder in both children and adults. In this article we examine whether, by using a sample of middle-aged male twin veterans, the phenotypic characterization, prevalence, heritability and the longitudinal course of the illness is comparable to results observed in samples of children and adolescents. We evaluated the utility of adult reports of lifetime ADHD symptoms by examining the heritability of retrospectively reported childhood symptoms, using both symptom-based and discrete classification- based approaches, as well as examining the persistence of ADHD symptoms into adulthood for that subsample of individuals who were judged to possibly have ADHD as children. Our results showed prevalence rates that were approximately similar to those observed in other studies, demonstrable familiality, similar item endorsement patterns, a strong genetic association between hyperactive and inattentive subtypes, and a longitudinal decline in symptom severity. We concluded that while assessing ADHD in adult probands may be less accurate than with children or adolescents, since it demonstrates several characteristics in common with other assessment techniques it remains a viable diagnostic and research strategy, even with population samples.

Genetic and Environmental Influences on the Associations Between Attention Problems and Other Problem Behaviors

Problem behavior in children shows a high degree of cooccurrence, both within the domains of internalizing and externalizing behaviors and across domains. Maternal ratings of 207 same- and opposite-sex twin pairs on the Child Behavior Checklist (CBCL/4–18; Achenbach, 1991) were used to determine the etiology of these associations. In the current sample of 4- to 11-year-old children (mean age: 7.6 years) phenotypic correlations were .68 between Internalizing and Externalizing, between .41 and .66 within the internalizing scales, and between .58 and .71 within the externalizing scales. Correlations across domains on the scale level were of similar magnitude. Genetic and shared environmental correlations were generally high, with the exception of the somatic complaints scale which showed low genetic correlations with other scales. These findings of uniformly high shared etiology was seen within and across domains. For example, Attention Problems showed genetic correlations of .65 with Delinquent Behavior and .76 with Aggressive Behavior; the genetic correlations of Attention Problems with internalizing scales were .71 for Anxious/Depressed and .79 for Withdrawn; a low genetic correlation was only shown for the Somatic Complaints scale (rg = .16). Although the magnitude of shared environmental contributions was lower, the environmental correlations were close to unity, indicating that the same family environmental factors were involved in aspects of problem behavior when assessed across domains. Results for the Attention Problems scale were similar to other disruptive behavior, justifying its inclusion with the externalizing scales.

Estimation of Prevalence of DSM-IV and Latent Class-Defined ADHD Subtypes in a Population-Based Sample of Child and Adolescent Twins

The goal of this study is to determine the prevalence and age of onset of Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSMIV; American Psychiatric Association, 1994) and latent class-derived attention deficit/hyperactivity disorder (ADHD) subtypes in a population-based twin sample of boys and girls. Missouri birth records identified families with a twin pair 7 to 18 years of age. Telephone screening interviews for ADHD symptoms were completed for 5007 families. Diagnostic assessments were administered to 564 families with at least one twin meeting screening criteria, plus 183 control families. Prevalence and age of onset for both ADHD nosologies were calculated by sex and zygosity from parent report data. The prevalence of any DSM-IV ADHD was 6.2% overall, 7.4% in boys and 3.9% in girls. The inattentive subtype was most common in boys; the combined subtype was most common in girls. The mean age of onset of symptoms in children with any DSM-IV ADHD was 3.5 years, with no significant differences between boys and girls. Prevalences of latent class defined ADHD subtypes also varied by sex with the severe inattentive and combined classes more common in boys than girls. The age of onset of symptoms did not differ between boys and girls but were higher than in the DSM-IV subtypes. Findings in this twin sample showed that clinically significant ADHD, defined by either DSM-IV or latent class criterion, has an early age of onset and is more common in boys than girls. As clinical samples are most commonly composed of male combined subtypes, the inattentive subtype of both sexes in the general population is an under- treated segment of the general population.

Transferrin in korean children with attention deficit hyperactivity disorder

OBJECTIVE

The aim of the present study was to investigate the relationship between iron, ferritin, transferrin, total iron binding capacity (TIBC), hemoglobin, mean corpuscular volume (MCV) mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) in children with ADHD.

METHODS

MethodsaaThe sample consisted of 48 ADHD children and sex and age matched control children (a couple of 28 boys, 22 girls; age 6-8 years; mean±SD, 6.98±0.39). We diagnosed ADHD according to DSM-IV. ADHD symptoms were evaluated subjectively with Conners' Parent Rating Scales, Dupaul Parent ADHD Rating Scales. Subjects with ADHD and control were evaluated the hematology test including the iron, transferrin, MCV etc. Paired t test were used to evaluate the relation of a lot of hematology findings between ADHD and control group.

RESULTS

The serum iron, ferritin, transferrin, TIBC, hemoglobin, MCV, MCH, and MCHC of ADHD group were respectively 80.92±33.33 ug/dL, 35.81±16.59 ng/mL, 248.42±44.15 mg/dL, 351.69±102.13 ug/dL, 12.78±0.71 g/dL, 82.94±2.58 fL, 27.18±1.12 uug, 32.79±1.12%. Otherwise the serum iron, ferritin, transferrin, TIBC, hemoglobin, MCV, MCH, and MCHC of control group were respectively 82.04±28.14 ug/dL, 37.05±18.28 ng/mL, 266.27±25.40 mg/dL, 352.77±89.54 ug/dL, 12.77±0.70 g/dL, 81.81±2.96 fL, 26.69±0.99 uug, 32.66±0.96%. A significant difference were found in the transferrin(t=2.63, p=0.011), MCV (t=2.19, p=0.034), and MCH (t=2.18, p=0.034).

CONCLUSION

These results suggested that lower transferrin levels might be related with ADHD symptoms.

Heritability of insomnia symptoms in youth and their relationship to depression and anxiety

STUDY OBJECTIVES

Insomnia is a highly prevalent sleep disorder yet little is known about the role of genetic factors in its pathophysiology. The aim of this study was to examine the relative contributions of genetic and environmental factors in explaining variability in insomnia symptoms.

DESIGN

Traditional twin design.

SETTING

Academic medical center.

PARTICIPANTS

1412 twin pairs aged 8-16 years (48.8% MZ, 47.2% DZ, 4.0% indeterminate).

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Ratings of insomnia symptoms, depression, and overanxious disorder were made by trained interviewers based on DSM-III-R criteria. ACE models were conducted using Mx statistical software. Insomnia symptoms were prevalent in this sample based both on parental (6.6%) and youth (19.5%) reports. The overall heritability of insomnia symptoms was modest (30.7%), with the remaining variance attributed to unique environmental effects. There was no evidence of sex differences in the prevalence of insomnia symptoms or in the contribution of genetic and environmental effects. In multivariate models, there was support for insomnia-specific unique environmental effects over and above overlapping effects with depression and overanxious disorder, but no evidence for insomnia-specific genetic effects.

CONCLUSIONS

Genetic factors play a modest role in the etiology of insomnia symptoms in 8-16 year-olds. These effects overlap with the genetics of depression and overanxious disorder. Further work is needed to determine which genes confer risk for all three disorders.

Sex differences in the genetic and environmental influences on childhood conduct disorder and adult antisocial behavior

Sex differences in the genetic and environmental influences on childhood conduct disorder and adult antisocial behavior were examined in a large community sample of 6,383 adult male, female, and opposite-sex twins. Retrospective reports of childhood conduct disorder (prior to 18 years of age) were obtained when participants were approximately 30 years old, and lifetime reports of adult antisocial behavior (antisocial behavior after 17 years of age) were obtained 8 years later. Results revealed that either the genetic or the shared environmental factors influencing childhood conduct disorder differed for males and females (i.e., a qualitative sex difference), but by adulthood, these sex-specific influences on antisocial behavior were no longer apparent. Further, genetic and environmental influences accounted for proportionally the same amount of variance in antisocial behavior for males and females in childhood and adulthood (i.e., there were no quantitative sex differences). Additionally, the stability of antisocial behavior from childhood to adulthood was slightly greater for males than females. Though familial factors accounted for more of the stability of antisocial behavior for males than females, genetic factors accounted for the majority of the covariation between childhood conduct disorder and adult antisocial behavior for both sexes. The genetic influences on adult antisocial behavior overlapped completely with the genetic influences on childhood conduct disorder for both males and females. Implications for future twin and molecular genetic studies are discussed.

Parental depression and offspring psychopathology: a children of twins study

BACKGROUND

Associations between parental depression and offspring affective and disruptive disorders are well documented. Few genetically informed studies have explored the processes underlying intergenerational associations.

METHOD

A semi-structured interview assessing DSM-III-R psychiatric disorders was administered to twins (n=1296) from the Australian Twin Register (ATR), their spouses (n=1046) and offspring (n=2555). We used the Children of Twins (CoT) design to delineate the extent to which intergenerational associations were consistent with a causal influence or due to genetic confounds.

RESULTS

In between-family analyses, parental depression was associated significantly with offspring depression [hazard ratio (HR) 1.52, 95% confidence interval (CI) 1.20-1.93] and conduct disorder (CD; HR 2.27, CI 1.31-3.93). Survival analysis indicated that the intergenerational transmission of depression is consistent with a causal (environmental) inference, with a significant intergenerational association in offspring of discordant monozygotic (MZ) twin pairs (HR 1.39, CI 1.00-1.94). Logistic regression analysis suggested that the parental depression-offspring CD association was due to shared genetic liability in the parents and offspring. No intergenerational association was found when comparing the offspring of discordant MZ twins [odds ratio (OR) 1.41, CI 0.63-3.14], but offspring of discordant dizygotic (DZ) twins differed in their rates of CD (OR 2.53, CI 0.95-6.76). All findings remained after controlling for several measured covariates, including history of depression and CD in the twins' spouses.

CONCLUSIONS

The mechanisms underlying associations between parental depression and offspring psychopathology seem to differ depending on the outcome. The results are consistent with a causal environmental role of parental depression in offspring depression whereas common genetic factors account for the association of parental depression and offspring CD.

Parents and teachers make different contributions to a shared perspective on hyperactive-impulsive and inattentive symptoms: a multivariate analysis of parent and teacher ratings on the symptom domains of ADHD

Attention deficit hyperactivity disorder (ADHD) is characterised by developmentally inappropriate and impairing levels of inattentive and hyperactive–impulsive behaviours. We aimed to investigate the differential effects of parent and teacher ratings on inattention and hyperactivity–impulsivity and the extent of genetic overlap between the two behavioural dimensions. Multivariate structural equation modelling was performed on DSM-IV based ADHD ratings by parents and teachers collected on a general population sample of 672 twin pairs, at ages 7–10 years. This study is the first to simultaneously use parent and teacher ratings in twin modelling to examine the effects of different raters on the two behavioural dimensions of ADHD. The findings indicated that hyperactivity–impulsivity and inattention load on to separate latent factors that represent a common behavioural view for both parents and teachers, although there are additional aspects to the observations of these behaviours that are unique to each type of rater. The findings further indicate some shared aetiology for hyperactivity–impulsivity and inattention as measured by both parent and teacher ratings, in agreement with previous findings on the aetiology of the two symptom dimensions of ADHD.

Clinical effects of korean red ginseng on attention deficit hyperactivity disorder in children: an observational study

We investigated the clinical effects of Korean red ginseng on attention deficit hyperactivity disorder (ADHD) in children. Eighteen subjects aged between 6 and 14 diagnosed with ADHD based on the Diagnostic and Statistical Manual of Mental Disorders, fourth edition diagnosis criteria were enrolled. Korean red ginseng (Panax ginseng) at 1,000 mg b.i.d. was administered to the subjects for 8 weeks. Eighteen children completed the questionnaire and clinical assessment by visiting the hospital at baseline, then in the first, fourth and eighth weeks. Clinical assessments were performed by using the ADHD Diagnostic System (ADS, a computerized attention assessment program), the abbreviated Conners' rating scale in addition to psychiatric interviews. After 8 weeks, significant differences were found in the omisssion errors of ADS (78.56±43.33 at baseline, 55.17±21.44 at 8 weeks, p<0.023), Conners ADHD Rating Scale (13.78±6.32 at baseline, 9.50±4.80 at 8 weeks, p<0.042) and Spielberger State Anxiety Scale (30.94±6.25 at baseline, 28.83±6.23 at 8 weeks, p<0.024). In the Korean Personality Inventory for Children, a significant reduction of score was found in the physical development scale (56.44±9.63 at baseline, 50.94±8.91 at 8 weeks, p<0.017) and social dysfunction scale (56.33±6.82 at baseline, 51.94±7.13 at 8 weeks, p<0.025). These results suggest that Korean red ginseng may be effective in improving inattentiveness in ADHD children, but it remains uncertain if it improves the general severity of ADHD, depression, anxiety personality and behavioral changes.

Structure and etiology of co-occurring internalizing and externalizing disorders in adolescents

Several studies suggest that a two-factor model positing internalizing and externalizing factors explains the interrelationships among psychiatric disorders. However, it is unclear whether the covariation between internalizing and externalizing disorders is due to common genetic or environmental influences. We examined whether a model positing two latent factors, internalizing and externalizing, explained the interrelationships among six psychiatric disorders (major depressive disorder, generalized anxiety disorder, separation anxiety disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and conduct disorder) in adolescents, and whether there are common genetic and environmental influences on internalizing and externalizing latent factors. Multivariate behavior genetic analyses of data from 1162 twin pairs and 426 siblings ascertained from the general population via the Colorado Center for Antisocial Drug Dependence (CADD) were conducted. We found support for a model positing two latent factors (internalizing and externalizing). These factors were moderately heritable and influenced by significant common genetic and nonshared environmental influences. These findings suggest that co-occurrence of internalizing and externalizing psychopathology in adolescents results from both genetic and environmental influences.

The impact of study design and diagnostic approach in a large multi-centre ADHD study: Part 2: Dimensional measures of psychopathology and intelligence

BACKGROUND

The International Multi-centre ADHD Genetics (IMAGE) project with 11 participating centres from 7 European countries and Israel has collected a large behavioural and genetic database for present and future research. Behavioural data were collected from 1068 probands with ADHD and 1446 unselected siblings. The aim was to describe and analyse questionnaire data and IQ measures from all probands and siblings. In particular, to investigate the influence of age, gender, family status (proband vs. sibling), informant, and centres on sample homogeneity in psychopathological measures.

METHODS

Conners' Questionnaires, Strengths and Difficulties Questionnaires, and Wechsler Intelligence Scores were used to describe the phenotype of the sample. Data were analysed by use of robust statistical multi-way procedures.

RESULTS

Besides main effects of age, gender, informant, and centre, there were considerable interaction effects on questionnaire data. The larger differences between probands and siblings at home than at school may reflect contrast effects in the parents. Furthermore, there were marked gender by status effects on the ADHD symptom ratings with girls scoring one standard deviation higher than boys in the proband sample but lower than boys in the siblings sample. The multi-centre design is another important source of heterogeneity, particularly in the interaction with the family status. To a large extent the centres differed from each other with regard to differences between proband and sibling scores.

CONCLUSIONS

When ADHD probands are diagnosed by use of fixed symptom counts, the severity of the disorder in the proband sample may markedly differ between boys and girls and across age, particularly in samples with a large age range. A multi-centre design carries the risk of considerable phenotypic differences between centres and, consequently, of additional heterogeneity of the sample even if standardized diagnostic procedures are used. These possible sources of variance should be counteracted in genetic analyses either by using age and gender adjusted diagnostic procedures and regional normative data or by adjusting for design artefacts by use of covariate statistics, by eliminating outliers, or by other methods suitable for reducing heterogeneity.

Developmental pathways in oppositional defiant disorder and conduct disorder

The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV; American Psychiatric Association, 1994) specifies a developmental relationship between oppositional defiant disorder (ODD) and conduct disorder (CD). Evidence for this link is mixed, however, and recent studies suggest that different symptom dimensions in ODD may have different outcomes. The authors examined links between ODD, CD, and their young adult outcomes in the Great Smoky Mountains Study (E. J. Costello et al., 1996), a longitudinal data set with over 8,000 observations of 1,420 individuals (56% male) covering ages 9-21 years. ODD was a significant predictor of later CD in boys but not in girls after control for comorbid CD and subthreshold CD symptomatology. Transitions between ODD and CD were less common than anticipated, however, particularly during adolescence. The authors examined characteristics and outcomes of children with pure ODD, pure CD, and combined CD/ODD. Alongside many similarities in childhood and adolescent correlates, key differences were also identified: CD largely predicted behavioral outcomes, whereas ODD showed stronger prediction to emotional disorders in early adult life. Factor analysis identified irritable and headstrong dimensions in ODD symptoms that showed differential prediction to later behavioral and emotional disorders. Overall, the results underscore the utility of retaining separate ODD and CD diagnoses in DSM-V.

Gene-environment interactions: early life stress and risk for depressive and anxiety disorders

RATIONALE

Prior reviews have examined how stress, broadly defined, interacts with genetic diathesis in the pathogenesis of internalizing (i.e., depressive and anxiety) disorders. Recent findings have suggested a unique role for early life stress (ELS) in the development of internalizing disorders, contributing to the rapid proliferation of research in this area.

OBJECTIVE

This paper critically reviews studies in humans examining gene-environment interaction (GxE) effects of ELS on the risk for depression and anxiety, primarily from a candidate gene perspective. Major methodological challenges that are unique to such studies are considered.

RESULTS

The majority of published studies have focused on candidates that regulate the serotonin system, especially the serotonin transporter. More recent work has addressed interactions of ELS with candidates from the hypothalamic-pituitary-adrenal axis and neurotrophin system. Available studies vary greatly with respect to definitions of ELS, examination of gene-gene interactions, consideration of gender effects, and attention to analytic limitations.

CONCLUSIONS

Overall, there is support for GxE effects of ELS on the risk for depressive and anxiety outcomes. Future studies of ELS in this context will require careful attention to methodologic considerations. Such studies would benefit from more systematic assessment of positive environmental factors (e.g., social support) and greater utilization of developmentally sensitive paradigms.

The association between parent-child conflict and adolescent conduct problems over time: results from a longitudinal adoption study

A handful of prior adoption studies have confirmed that the cross-sectional relationship between child conduct problems and parent-child conflict at least partially originates in the shared environment. However, as the direction of causation between parenting and delinquency remains unclear, this relationship could be better explained by the adolescent's propensity to elicit conflictive parenting, a phenomenon referred to as an evocative gene-environment correlation. In the current study, the authors thus examined the prospective relationship between conduct problems and parent-child conflict in a sample of adoptive families. Participants included 672 adolescents in 405 adoptive families assessed at 2 time points roughly 4 years apart. Results indicated that parent-child conflict predicts the development of conduct problems, whereas conduct problems do not predict increases in parent-child conflict. Such findings suggest that evocative gene-environment correlations are highly unlikely to be an explanation of prior shared environmental effects during adolescence. Moreover, because the adolescents in this study do not share genes with their adoptive parents, the association between conduct problems and parent-child conflict is indicative of shared environmental mediation in particular. Implications of the findings are discussed.

Changes in genetic and environmental influences on the development of nicotine dependence and major depressive disorder from middle adolescence to early adulthood

This longitudinal study used a representative community sample of same-sex twins (485 monozygotic pairs, 271 dizygotic pairs) to study longitudinal changes in genetic and environmental influences on nicotine dependence (NicD) symptoms and major depressive disorder (MDD) symptoms and the longitudinal relationships between NicD and MDD symptoms at three relatively discrete ages spanning middle adolescence to early adulthood (ages 15, 18, and 21). Clinical interviews were used to assess NicD and MDD symptoms lifetime at age 15 and during the previous 3 years at the two subsequent assessments. Biometric models revealed similar patterns of findings for NicD and MDD. Heritability increased with age, particularly between ages 15 and 18. Shared environmental influences were small, and the proportion of variance attributed to shared environmental influences decreased with age. Nonshared environmental influences were moderate to large in magnitude and were entirely age specific. Both NicD and MDD symptoms showed considerable stability from age 15 to 21, and at each age those with one disorder showed elevated rates of the other. However, a cross-lagged model revealed no longitudinal predictive relationships between MDD symptoms and NicD symptoms after accounting for stability of symptoms within disorders. In summary, the transition between middle and late adolescence is a critical period for developmental shifts in the magnitudes of genetic and environmental influences on both MDD and NicD symptoms. Despite similarities in the development of genetic and environmental influences for the two phenotypes, the association between NicD and MDD reflects concurrent covariation rather than one phenotype being an antecedent influence on the subsequent development of the other.

The Role of Attention-Deficit/hyperactivity Disorder in the Association between Verbal Ability and Conduct Disorder

Although there is clear evidence that low verbal ability is a risk factor for conduct disorder (CD), some researchers have questioned whether this association is due to the common comorbidity between attention-deficit/hyperactivity disorder (ADHD) and CD. The present study examined the association among verbal ability, ADHD, and CD in a genetically informative sample in order to examine the role of genes and/or environmental influences shared in common with ADHD on the covariation between verbal ability and CD. Participants were 2744 adolescents from the Center for Antisocial Drug Dependence (CADD), and included 360 monozygotic (MZ) female twin pairs, 221 dizygotic (DZ) female twin pairs, 297 MZ male twin pairs, 220 DZ male twin pairs, and 274 opposite-sex DZ twin pairs. The Diagnostic Interview Schedule for Children (DISC-IV) was used to assess lifetime symptoms of ADHD and CD. Verbal ability was assessed via the Vocabulary subtest of the Wechsler Adult Intelligence Scale III (WAIS-III) for individuals over the age of 16 and the Vocabulary subtest of the Wechsler Intelligence Scale for Children III (WISC-III) for individuals under the age of 16. There was a small but significant negative covariance between verbal ability and CD and between verbal ability and ADHD. Results also suggest that the covariation between verbal ability and CD is due to influences shared in common with ADHD.

The representation of early onset depression by ICD-9 and ICD-10 categories

BACKGROUND

Concepts of affective disorders have not received substantial validation in childhood and adolescence even after the theoretical separation between neurotic and endogenous depression was changed. The aim of this study was to assess differences in children and adolescents with neurotic and endogenous depression according to ICD-9 and depression according to ICD-10 with regard to the severity of different symptoms as well as anamnestic and psychosocial risk factors.

SAMPLING AND METHODS

Data of 33 and 88 patients (classified according to ICD-9 and ICD-10, respectively) with a confirmed diagnosis of depression were included. In a standardized study protocol, sociodemographic data, family history, psychopathological symptoms and psychosocial and environmental factors were analyzed.

RESULTS

Patients diagnosed with endogenous depression more frequently had a positive family history of psychiatric disorders and had more comorbid symptoms in comparison to those with neurotic depression. Group comparisons of the ICD-9 and ICD-10 demonstrated fewer abnormal psychosocial and environmental factors and fewer affective symptoms in the ICD-9 sample. Logistic regression revealed predictors for endogenous depression in the ICD-9 sample and severe depression in the ICD-10 sample.

CONCLUSIONS

Neurotic depression might represent a subthreshold depression diagnosis compared with endogenous depression. The present study was limited by small and different sample sizes and the fact that dysthymia was not classified within the ICD-10 diagnosis.