Assessment of genetic and environmental influences on differential ratings of within-family experiences and relationships in twins.

BACKGROUND: Although there is evidence that genetic factors influence individual differences in environmental risk exposure, there are few findings on genetic effects on differential parenting. The present study sought to examine this issue. METHODS: The sample comprised 1,117 pairs of like-sex male and female twins, aged 8-16 years, and their parents, recruited from the school population of Virginia. Differential ratings of the within-family experiences were provided by the Twin Inventory of Relationships and Experiences (TIRE). RESULTS: Dimensions describing the within-family environment based on differential ratings contrasting the twins with one another, were influenced, to an approximately equal extent, by both genetic and environmental factors. CONCLUSIONS: The findings suggest that genetic differences between like-sex siblings lead them to experience their family environment differently, but also that environmental influences significantly affect interactions within the family.

Comparing the biological and cultural inheritance of personality and social attitudes in the Virginia 30,000 study of twins and their relatives.

Measures of four dimensions of personality (Psychoticism, Extraversion, Neuroticism, and Lie scores) and six aspects of social attitudes (to sex, taxation, militarism, politics, religion and a general conservatism scale) were obtained by mailed questionnaire from 29,691 US subjects including adult twins (n = 14,761) their parents (n = 2360), their spouses (n = 4391), siblings (n = 3184) and adult children (n = 4800). After correction for the average effects of age, sex and source of sample, familial correlations were computed for 80 distinct biological and social relationships. The data allow for the estimation of the additive and non-additive effects of genes, assortative mating, vertical cultural inheritance and other non-parental effects of the shared environment on differences in personality and social attitudes. The interaction of genetic and environmental effects with sex may also be analyzed. Model-fitting analyses show that personality and social attitude measures differ markedly in major features of family resemblance. Additive and dominant genetic effects contribute to differences in both personality and attitudes, but the effects of the family environment, including vertical cultural transmission from parent to child, are much more marked for social attitudes than for personality. There is substantial assortative mating for social attitudes and almost none for personality. The causes of family resemblance depend significantly on sex for almost every variable studied. These findings clarify and extend the more tentative findings derived from previous twin, family and adoption studies.

Genetics and developmental psychopathology: 1. Phenotypic assessment in the Virginia Twin Study of Adolescent Behavioral Development.

We introduce an overlapping cohort sequential longitudinal study of behavioral development and psychopathology in a representative sample of 1412 pairs of twins aged 8 through 16 years. Multiple phenotypic assessments involve a full psychiatric interview with each child and each parent, and supplementary parental, teacher, and child interview material and questionnaires. For the first wave of assessments, the numbers of reported DSM-III-R symptoms of Major Depressive Disorder (MDD), Separation Anxiety Disorder (SAD), Overanxious Disorder (OAD), Oppositional Defiant Disorder (ODD), Conduct Disorder (CD), and Attention Deficit Hyperactivity Disorder (ADHD), assessed through interviews, confirm patterns of age and sex trends found in other epidemiological samples, but underscore their dependence on whether the child or the parent is the informant. Correlations across domains for symptoms reported by the same informant are often as large as correlations across informants for the same domain of symptoms. Factor analyses of these symptom counts, taking account of informant view and unreliability of assessment, show the high degree of correlation between SAD and OAD, between MDD and OAD, and between CD and ODD. ADHD symptoms are relatively independent of the other domains, but show moderate correlations with CD, ODD, and MDD. Factorially derived dimensional questionnaire scales, based on child, parental, and teacher reports, show patterns of relationship to symptom counts consistent with both convergent and discriminant validity as indices of liability to clinical symptoms. Across informants, questionnaire scales provide as good a prediction of symptoms as do clinical interviews. Multitrait-multimethod confirmatory factor analysis reveals the patterns of relationship between symptoms of psychiatric disorder in children taking due account of informant and unique sources of variance. Gender differences are consistent within the correlated clusters of ODD/CD and MDD/SAD/OAD, although there are disorder-specific age trends. There are large informant-specific influences on the reporting of symptoms in clinical interviews. Dimensional questionnaire scales provide a useful source of additional information. In subsequent analyses of genetic and environmental etiology of childhood psychopathology we must expect that results may differ by informant and method of assessment. Multivariate and developmental analyses that explore the sources of these differences will shed new light on the relationship between genetic and environmentally influenced vulnerability and the manifestation of psychopathology in specific circumstances.

A twin study of recent life events and difficulties.

OBJECTIVES: To examine the role of genetic and familial-environmental factors in the origin of stressful life events. DESIGN: Self-report questionnaires describing stressful life events in the last year. PARTICIPANTS: Both members of 2315 twin paris ascertained from the population-based Virginia Twin Registry. RESULTS: Life events were modestly but significantly correlated in twin pairs, and correlations in monozygotic (MZ) twins consistently exceeded those in dizygotic (DZ) twins. For total life events, the best-fitting twin model indicated that familial-environmental and genetic factors each accounted for around 20% of the total variance. Individual life events could be best divided into "network events" (directly affecting individuals in the respondent's social-network) where twin resemblance was due solely to the familial environment, and "personal" events (directly affecting the response) where most twin resemblance was the result of genetic factors. CONCLUSIONS: While neither genes nor familial environment is likely to directly produce life events, personal and social factors that predispose to life events are substantially influenced by an individual's genetic and family background. These results, which suggest that stressful life events reflect more than random influences, may have important implications for our understanding of the relationship between stressful life events and psychopathology.

Education policy and the heritability of educational attainment.

Many workers assume that genetically determined differences in intellectual ability will be influenced little by changes in educational policy or other environmental interventions. Others, however, have suggested that increasing equality of educational opportunity will lead to an increase in the heritability of educational attainment. The resolution of this issue has been delayed until now because of the extremely large sample sizes which would be required. Education data on twins and their parents, from the Norwegian twin panel, provide a unique opportunity to determine the impact on the heritability of educational attainment of the more liberal social and educational policies introduced in Norway after the Second World War. As reported here, for individuals born before 1940 there is a strong effect of family background on educational attainment, accounting for 47% of the variance, though genetic factors account for an additional 41% of the variance. For females born after 1940 and before 1961, the relative importance of genetic (38-45%) and familial environmental (41-50%) differences changes very little. For males born during the same period, the broad heritability of educational attainment has increased substantially (67-74%), and the environmental impact of family background has correspondingly decreased (8-10%). For males, at least, having well-educated parents no longer predicts educational success, as measured by duration of education, independent of the individual's own innate abilities.

Name-printing as a test of developmental maturity.

An attempt to derive a practical scoring technique for name-printing by children in kinderten (age-range 5 1/2 to 6 1/2 years) as a quick test of skills and maturity is reported. The relationship of the Print-Your-Name test scores to other established tools of developmental assessment is examined. Teachers' assessments of the study children's readiness for academic promotion and of those children with school problems tended to correlate with the test scores.