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

Genetic and environemental factors in conduct problems and adult antisocial behavior among adult female twins

Most twin and adoption studies of conduct problems have demonstrated modest genetic effects but substantial contributions of shared family environment. Conversely, most investigations have shown marked genetic influences but modest contributions of shared family environment in adult antisocial behavior. However, most previous work has focused on male subjects. We obtained retrospective reports of DSM-III-R-defined conduct disorder (CD) and adult antisocial behaviors from a population-based sample of female-female twin pairs. Genetic and environmental contributions to conduct problems and adult antisocial behaviors were examined using polychoric correlation coefficients and univariate structural equation modeling. Statistically significant but modest heritability was observed for conduct problems. A small, statistically nonsignificant contribution of shared family environment to CD behavior was also noted. Adult antisocial symptoms showed modest contributions of both additive genetic and shared family environmental factors. In both childhood and adulthood, the largest influence on antisocial behavior was individual-specific environment. Our findings support the importance of both genetic and environmental factors in antisocial behavior among women as well as the possibility that the relative importance of each set of influences differs by sex in both childhood and adulthood.

Heritability and the comorbidity of attention deficit hyperactivity disorder with behavioral disorders and executive function deficits: a preliminary investigation

The heritability and comorbidity of attention deficit hyperactivity disorder (ADHD) with conduct disorder (CD), oppositional defiant disorder (ODD), and executive function (EF) deficits were examined in 224 child twins (140 monozygotic and 84 dizygotic). The Coolidge Personality and Neuropsychological Inventory for Children (Coolidge, 1998), a standardized, 200-item, Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) aligned, parent-as-respondent inventory, assessed psychopathology. Structural equation model fitting revealed that the individual scale heritabilities were substantial: .82 for ADHD, .74 for CD, .61 for ODD, and .77 for EF deficits. The results of the multivariate twin analyses suggest that ADHD shares most of its genetic liability with CD, ODD, and EF deficits. Thus, the findings argue for a common biological risk underlying these commonly comorbid externalizing behavior problems and cognitive deficits. The residual genetic variance provides preliminary support for additional genetic influences underlying CD, ODD, and EF that are independent of ADHD.

Does the definition of ADHD affect heritability?

OBJECTIVE

A twin study design was used to examine the genetic validity of attention-deficit hyperactivity disorder (ADHD)-related phenotypes.

METHOD

Questionnaires covering ADHD symptoms were sent to the families of 2,846 school-age twins. Parent-rated symptoms were obtained for 2,082 twin pairs and teacher-rated symptoms were available for 1,470 twin pairs.

RESULTS

Broadly defined parent-rated, teacher-rated, and "pervasive" (both parent- and teacher-rated) ADHD categories were found to be highly heritable. Significant shared environmental effects were also detected for teacher-rated ADHD. A common genetic factor was found to have a modest influence on both parent- and teacher-rated symptom scores and categories, but additional genetic and environmental influences were also found forteacher-rated ADHD. Consistent with previous findings, ADHD symptom scores were again found to be highly heritable. Maternal contrast effects were found for the Rutter A scale items but could not be detected for the DuPaul ADHD rating scale.

CONCLUSIONS

Broadly defined pervasive ADHD appears to be as heritable as ADHD behaviors defined by maternal reports alone. A common genetic factor influences maternally rated and teacher-rated ADHD but does not account for all of the genetic variance for teacher-rated ADHD. ADHD symptom scores are highly heritable, and maternal contrast effects appear to vary for different measures.

Evidence for a genetic etiology of early-onset delinquency

Age at onset of antisocial behavior discriminates persistent and transitory offenders. The authors proposed that early-onset delinquency has an underlying genetic influence that manifests in problems related to inhibition, whereas late-onset delinquency is more environmentally mediated. To test these notions, they selected 36 early starters, 86 late starters, and 25 nondelinquent controls from a large sample of 11-year-old twins and compared them on several measures related to inhibition and a peer group measure. As expected, early starters had more psychological, behavioral, and emotional problems related to inhibition than late starters and controls. A longitudinal analysis indicated an increase an antisocial behavior among peers of late starters shortly before their delinquency onset. Family history data and a twin analysis provided evidence of greater genetic influence on early-onset than late-onset delinquency.

Role of the family in the onset and outcome of childhood disorders: selected research findings

OBJECTIVE

Three areas of basic family research were selected for review as being of special importance to the clinically oriented child and adolescent psychiatrist: behavioral genetics, expressed emotion, and the interaction of family dynamics and childhood illness.

METHOD

Medline and PSYCINFO searches using appropriate keywords were obtained for each of the 3 major areas. All English-language articles published after 1989 that included empirical research pertaining to children or adolescents were reviewed.

RESULTS

Behavioral genetics research indicates that the shared environment, including issues of parental monitoring and discipline, is important in the development and outcome of externalizing disorders. Differential parental treatments of one sibling are critical in internalizing disorders. Criticism (as measured by expressed emotion) is associated with poor outcome of many childhood medical and psychiatric disorders. Chronic illness in a child changes the family dynamics toward being more structured and less emotionally warm and communicative. The family's role in adherence to treatment is critical, and families with high levels of criticism have more difficulty.

CONCLUSIONS

Families can cause problems, but many times the problems families have are in response to a child's problems. There is a continued need to empirically assess which family processes are important for specific childhood disorders.

Extracting meaning from comorbidity: genetic analyses that make sense

As behavioral genetic strategies have become part of the arsenal of research in developmental psychopathology, a wide variety of genetic analyses are being applied to child psychiatric data. Multivariate genetic techniques have been used to explore comorbidity among traits or disorders and the main analysis undertaken has been to examine whether comorbidity is due to shared genetic and/or environmental factors. However, this model ignores other possible causes of comorbidity, which are reviewed. In particular, genetic analyses of comorbidity have only infrequently considered the model of phenotypic causality (one disorder directly influencing another), which provides an important alternative with potentially different implications for intervention strategies. Data from a recently published article by Wamboldt, Schmitz, and Mrazek (1998) are used to illustrate the potential difficulties of distinguishing between models of shared genetic/environmental risk and phenotypic causality. Given that the sample sizes required to distinguish between these models are often large, and frequently greater than those of the datasets available, it is argued that researchers should select the models that they test based on other lines of evidence that these models are plausible. Where convincing evidence does not exist, researchers should explore alternative models and determine their power to discriminate between these models.

Association and linkage of DRD4 and DRD5 with attention deficit hyperactivity disorder (ADHD) in a sample of Turkish children

The search for genetic factors predisposing to Attention Deficit Hyperactivity Disorder (ADHD) has focused on genes that regulate dopaminergic pathways such as dopamine receptors and enzymes that regulate levels of dopamine in the synapse. There have been several reports of association between ADHD and polymorphic variants within or near DRD4, DRD5, DAT1, DBH and COMT. In this study we set out to investigate specific alleles of DRD4 and DRD5, previously reported to be associated with ADHD, in a sample of Turkish children with DSM-IV ADHD children, as well as their relation to methylphenidate response and dimensional measures of symptom domains. One hundred and four independent trios and seven dyads were analysed using the transmission disequilibrium test (TDT). We found increased transmission of the DRD4 7-repeat allele (DRD4*7) (TDT chi2 = 2.79, P = 0.047). Given that we were testing specific a priori hypotheses regarding the associated alleles, we have used one-tailed P-values throughout. There was evidence of an interaction with methlyphenidate (MPH) response and analysis of the sample excluding non-responders revealed more significant evidence for the association (TDT chi2 = 4.48, P = 0.017). We also detected a trend for linkage and association in the DRD5 polymorphism (TDT chi2 = 2. 38, P = 0.06). Similar findings were obtained in relation to MPH response as analysis of MPH responders alone gave rise to a more significant association than that of the group as a whole (TDT chi2 = 4.9, P = 0.013). t-Test and logistic regression TDT analyses of DRD4*7 transmission with respect to dimensional rating scales of hyperactivity and impulsivity showed an inverse relation suggesting that in this sample DRD4*7 is associated with a lower level of ADHD symptomatology. While this may be due to stratification along a dimension of severity such that severe cases belong to a more extreme group with other specific genetic and environmental causes, similar to the model for low cognitive ability, it is more likely the result of a chance selection bias in this sample.

Hypescheme: an operational criteria checklist and minimum data set for molecular genetic studies of attention deficit and hyperactivity disorders

Investigators engaged in mapping the genetic basis of attention deficit hyperactivity disorder (ADHD) currently use a number of measures for the collection of clinical information. This gives rise to difficulties in comparing datasets and research communications between independent groups. This paper describes the development of Hypescheme, which is an operational criteria checklist for ADHD, oppositional defiant disorder (ODD), and conduct disorder (CD), and is proposed as a minimum dataset for those engaged in molecular genetic studies of ADHD. Hypescheme consists of a computerised data checklist system that includes all the operational criteria required for both DSM-IV and ICD-10 diagnostic criteria and a systematic record of information about comorbid psychiatric, developmental, and neurological disorders. Using this data, an algorithm applies both DSM-IV and ICD-10 criteria to generate operational diagnostics under both these systems. Hypescheme is not designed to replace current assessment protocols but to be a final common checklist that can be completed by experienced researchers using all available data.

Etiology of inattention and hyperactivity/impulsivity in a community sample of twins with learning difficulties

A community sample of 373 8 to 18 year-old twin pairs in which at least one twin in each pair exhibited a history of learning difficulties was utilized to examine the etiology of inattention and hyperactivity/impulsivity (hyp/imp). Symptoms of attention-deficit/hyperactivity disorder (ADHD) were assessed by the DSM-III Diagnostic Interview for Children and Adolescents. Inattention and hyp/imp composite scores were created based on results of a factor analysis. Results indicated that extreme ADHD scores were almost entirely attributable to genetic influences across several increasingly extreme diagnostic cutoff scores. Extreme inattention scores were also highly heritable whether or not the proband exhibited extreme hyp/imp. In contrast, the heritability of extreme hyp/imp increased as a linear function of the number of inattention symptoms exhibited by the proband. This finding suggests that extreme hyp/imp may be attributable to different etiological influences in individuals with and without extreme inattention. If this result can be replicated in other samples, it would provide evidence that the hyp/imp symptoms exhibited by individuals with Combined Type ADHD and Predominantly Hyp/Imp Type ADHD may be attributable to different etiological influences.

A twin study of inattentive, aggressive, and anxious/depressed behaviors

OBJECTIVE

To estimate genetic, environmental, and rater contrast influences on parental report of Attention Problems (AP), Aggressive (Agg), and Anxious/Depressed (AxD) behaviors of 492 twin pairs assessed with the Child Behavior Checklist.

METHOD

A parent (92% mothers) of twins aged 8 to 12 years completed the Child Behavior Checklist. Genetic, shared and unique environmental, and rater bias effects were estimated for the AP, Agg, and AxD syndromes. Data on boys and girls were analyzed separately. Results were compared to prior research on related DSM disorders.

RESULTS

Estimates of genetic influences on AP (60%-68%), Agg (70%-77%), and AxD (61%-65%) were high for both sexes, but lower for AP than prior findings using DSM attention-deficit hyperactivity disorder (ADHD). However, unlike equivalent analyses of DSM ADHD based on parental report, there was no evidence of rater bias.

CONCLUSIONS

Estimates of genetic influence on these common child psychopathological domains were high. There was no evidence of rater contrast effects. These findings have implications for diagnosis, particularly when assessing families with multiple children.

Hyperactivity in children: a focus on genetic research and psychological theories

Hyperactivity has attracted a large amount of research interest in recent years. Here we review developments in genetic research and in research testing psychological theories of the condition. Family, adoptee and twin studies indicate a strong role for genetic factors in the etiology of hyperactivity. Evidence is emerging also from molecular genetic studies, implicating specific genes that may be involved. At the level of cognitive functioning, a divided, focused or sustained attention deficit does not seem to be a 'core' deficit in hyperactivity. Although children with hyperactivity often perform poorly on certain executive function tasks, there is disagreement about the interpretation of these findings. The association reported in some studies between a slow inhibitory process and hyperactivity may reflect a generally slow, variable in speed and inaccurate pattern of responding. Hypotheses about psychological mechanisms such as state regulation or delay aversion provide alternative, and particularly encouraging, interpretations of the findings. We discuss the possible integration of the two lines of research--those of genetic research and research on psychological mechanisms.

The Child and Adolescent Psychiatric Assessment (CAPA)

OBJECTIVE

To describe the Child and Adolescent Psychiatric Assessment (CAPA). The base interview covers the age range from 9 to 17 years.

METHOD

The interview glossary that provides detailed operational definitions of symptoms and severity ratings is described, and psychometric data and further developments of the interview are presented.

RESULTS

Across 5,962 parent-child interviews, the core sections of the CAPA (psychiatric symptoms, functional impairment, demographics, family structure and functioning) took on average 59 minutes for children and 66 minutes for parents. Test-retest reliability for diagnoses ranged from kappa = 0.55 for conduct disorder (CD) to kappa = 1.0 for substance abuse/dependence. Validity as judged by 10 different criteria was good. Developments of the CAPA include a shorter "gateway" version using core symptoms as screen items, a Spanish version, and versions for twin studies, use with young adults (YAPA), and preschool-age children (PAPA).

CONCLUSIONS

There is a place in both research and clinical settings for a rigorously operationalized interview (such as the CAPA) that focuses on ensuring that respondents understand what is being asked and on clearly defining levels of symptom severity and functional impairment.

Biologische Grundlagen von impulsiv-aggressivem Verhalten

Zusammenfassung. Früh beginnende aggressive Verhaltensstörungen, die zu den häufigsten psychischen Störungen zählen, sind zeitlich sehr stabil und haben unbehandelt eine schlechte Langzeitprognose. Sie gehen oft einher mit schwerwiegenden Störungen der Impulskontrolle und sind im Langzeitverlauf assoziiert mit anderen gravierenden Störungen. Als Ergebnis vielfältiger Studien kann die Entstehung aggressiven Verhaltens nur als Ergebnis eines multikausalen Geschehens verstanden werden, in das biologische, psychobiologische, psychologische, psychosoziale, soziologische und situative Einflußfaktoren eingreifen (siehe z.B. Robins, 1991 ; Raine, 1993 ; Renfrew, 1997 oder Frick, 1998 ). Die im folgenden dargestellten empirischen Ergebnisse beziehen sich nur auf einen Teil dieses multikausalen Prozesses, und zwar die biologischen Ursachen impulsiv-aggressiven Verhaltens. Beschrieben werden genetische Grundlagen, neurochemische und psychophysiologische Einflußfaktoren sowie Ergebnisse zu Interaktionen zwischen biologischen und psychosozialen Faktoren in der Genese von aggressivem Verhalten. Es wird die Notwendigkeit einer entwicklungspsychopathologischen Perspektive hervorgehoben, die von einer Interaktion oder Transaktion verschiedener Risiko- oder Einflußfaktoren ausgeht.

Using genetic analyses to clarify the distinction between depressive and anxious symptoms in children

Self-report measures of depression and anxiety in children are highly correlated and distinguishing between shared and independent factors in their etiologies is therefore problematic. The aim of this article was to test whether less correlated measures of depression and anxiety could be produced and, if so, what genetic and environmental factors would account for the variance in these symptoms. Second-order factor analysis of the items from two standardized self-report questionnaires of depression and anxiety collected from 395 pairs of same-sex twins aged 8 to 16 years resulted in purer dimensions of depression and anxiety. Behavioral genetic analyses confirmed the distinction between these two dimensions, and bivariate analyses revealed that the association between the two was primarily accounted for by shared genetic factors.

Development of gender differences in depression: description and possible explanations

This article reviews the description and possible explanations for the development of gender differences in depression in children and adolescents. The emerging gender difference (more girls depressed than boys) in depressed mood and depressive disorders appears after the age of 13 years or midpuberty. Currently, little evidence supports that biological factors are an explanation. Genetic factors are associated more strongly with depression among pubertal girls than boys. Regarding cognitive factors, ruminative response style, but not dysfunctional attitudes or attributional style, has been supported to be a possible explanation. Studies on childhood adversities and gender role have provided evidence explaining why more girls are depressed than boys. Girls are more likely to experience negative events in the family than boys, and these adversities are in turn associated with elevated depression. Girls identify more strongly with a feminine stereotype of needing to appear thin and consequently become more dissatisfied with their body shape and physical appearance, which in turn is associated with increased depression.

Genetic and environmental influences on ratings of manifest anxiety by parents and children

Parental reports and children's self-reports of manifest anxiety were obtained from a community-based sample of twin pairs on two occasions approximately 19 months apart, using the Revised Child Manifest Anxiety Scale (Reynolds & Richmond, 1978). In prior cross-sectional studies, a low degree of agreement between parent and child assessments of anxiety was found. Furthermore, parental reports were found to reflect a higher heritability than children's self-reports (Eaves et al., 1997; Thapar & McGuffin, 1995). The index of temporal stability was moderate for all informants (circa r = .5 to r = .6). To test whether the components contributing to the temporal stability differed between the informants, structural equation models were fitted to the data using the program, Mx: Statistical Modeling (Neale, 1995). The results showed substantial differences in genetic effects according to both gender and informant. For children's self-reports, temporal stability was largely a function of environmental effects, with genetic effects contributing a modest 20%, whereas for parental reports, temporal stability was largely a function of genetic effects. The heritability was higher for parental reports than for boys' self-reports and the genetic covariance between parents and their sons was near zero, indicating that they were reporting on quite different aspects of anxiety. However, for girls, heritability for maternal reports was lower than for self-reports, and the genetic covariance between mother and daughter was about the same as that between mothers and fathers, meaning that they were assessing the same genetically influenced aspect of anxiety. These results highlight the need to focus on gender differences.

Behavioral genetics as a tool for developmental psychology: anxiety and depression in children and adolescents

Over the past decade there has been a huge increase in the number of behavioral genetic studies looking into anxiety and depression in children and adolescents. There are now enough data in this area to make a review of the results useful. This paper begins with an outline of the methods used in such research and moves on to review the results in extant studies. Overall, these studies indicate modest to moderate genetic influence on both anxiety and depression. However, behavioral genetic methods are also paramount for exploring environmental influences in addition to genetic influences. Shared environment (that which makes family members resemble one another) is rarely identified in adult studies of personality or psychopathology and does not appear to be a significant influence for depression but it is for anxiety. Nonshared environment, which makes family members differ from one another, is found to be a significant influence for both anxiety and depression. Patterns within these results due to rater effects, age effects, sex effects, the precise phenotype measured, and the study design are explored.

Genetic basis of attention deficit and hyperactivity

BACKGROUND

Hyperkinetic disorder or attention-deficit hyperactivity disorder (ADHD) is an important clinical condition.

AIMS

The research evidence for a genetic contribution to ADHD is reviewed.

METHOD

Measurement of the phenotype, the extent to which attention deficit and hyperactivity are heritable and molecular genetic findings are discussed. Future research directions are also considered.

RESULTS

ADHD is a familial disorder. Available adoption evidence suggests genetic influences are important. Twin studies have primarily focused on trait measures which have consistently been found to be highly heritable Molecular genetic studies of clinical disorder so far have suggested the involvement of the dopamine DRD-4 receptor gene and dopamine transporter gene (DAT1). However, these findings await further replication.

CONCLUSIONS

Advances in psychiatric genetics and current research interest in the genetics of ADHD should improve our understanding of aetiological factors and have an impact on treatment.

Evaluation of ADHD typology in three contrasting samples: a latent class approach

OBJECTIVE

To identify subtypes of attention-deficit/hyperactivity disorder (ADHD) and characterize them as either categorical or continuous; to investigate familial resemblance for ADHD among sibling pairs; and to test the robustness of all results by using contrasting data sets.

METHOD

Latent class analysis was applied to the ADHD symptom profiles obtained from parents or best informant about their offspring in 3 samples: a population-based set of female adolescent twins (724 monozygotic pairs, 594 dizygotic pairs) and male (N = 425) and female (N = 430) child and adolescent offspring ascertained from high-risk alcoholic families.

RESULTS

Latent class analysis revealed 2 categories of clinically significant ADHD which were replicated in all 3 study groups: a subtype with high endorsements of ADHD inattention symptoms and a second combined type with high endorsements of both inattention and hyperactivity-impulsivity items. Both appeared to be continuous across all 3 data groups. The high-risk families contained a class in which members heavily endorsed the ADHD "fidget" item but not other ADHD items. A large proportion of the monozygotic sibs (80%) versus a smaller proportion of dizygotic sibs (52%) were assigned to the same latent class. Among the high-risk children and adolescents, 51% of the female and 41% of the male siblings were concordant for class membership.

CONCLUSIONS

The pattern of latent classes suggested that ADHD consists of an inattentive and a combined subtype, within each of which lies a dimensional domain. These analyses further support that genetic factors are significant determinants of latent class membership.

Latent class and factor analysis of DSM-IV ADHD: a twin study of female adolescents

OBJECTIVE

In an attempt to validate the current DSM-IV criteria for attention-deficit/hyperactivity disorder (ADHD) in females and to determine whether symptoms are continuously distributed or categorically discrete, the authors performed factor and latent class analysis on ADHD symptom data from a large general population of adolescent female twins (1,629 pairs).

METHOD

A structured diagnostic assessment of DSM-IV ADHD was completed with at least one parent of 1,629 pairs by telephone. ADHD symptoms from 1,549 pairs were subjected to latent class and factor analysis.

RESULTS

Latent class and factor analyses were consistent with the presence of separate continuous domains of inattention (ATT), hyperactivity-impulsivity (H-I), and combined ATT with H-I problems. Severe latent classes corresponding to the predominantly inattentive, predominantly hyperactive-impulsive, and combined types were identified with lifetime prevalence estimates of 4.0%, 2.2%, and 3.7%, respectively. Membership in the severe ATT class predicted academic problems, family problems, and referral to health care providers. Membership in the H-I and combined classes also predicted impaired social relationships.

CONCLUSIONS

These results suggest that DSM-IV ADHD subtypes can be thought of as existing on separate continua of inattention, hyperactivity-impulsivity, and combined type problems. Membership in any of there severe ADHD latent classes did not preclude academic excellence, but it was associated with different types of impairment and health care-seeking behavior. These data have implications in the areas of diagnosis, classification, treatment, and research.

Opportunities for psychiatry from genetic findings

BACKGROUND

The opportunities for psychiatry deriving from available or likely genetic advances are reviewed.

METHOD

Clinical implications are considered in the context of both the misconceptions and benefits associated with relevant genetic findings.

RESULTS

Misconceptions include that: heritability estimates have a 'true' fixed value; a high heritability means that environmental interventions will be ineffective; a high heritability within groups means that differences between groups will also be due to genes; genetic effects are determinative; 'genetic' means single abnormal genes; genes associated with disease must be bad and justify eugenic measures; gene therapy will be widely applicable; and genetic screening of the general population will be useful. The benefits include demonstrations that: both genes and environment have an ubiquitous influence; some prevailing diagnostic assumptions are mistaken; genes influence development; the effects of nature and nurture are not separate; and environmental effects tend to be person-specific. The potential value of molecular genetics lies in elucidation of causal processes as they apply to both brain systems and nature-nurture interplay; improving diagnosis and genetic counselling; and the development of improved pharmacological interventions.

CONCLUSION

Advances in genetics will make a major impact on clinical psychiatry, and should bring practical benefits for both prevention and treatment.