Genetic influence on life events during the last half of the life span.

Genetic influence of perceptions of major events later in life was assessed with a combination of twin and adoption designs as part of the Swedish Adoption/Twin Study of Aging (SATSA). The SATSA design includes 4 groups totaling 399 pairs of same-sex twins: identical and fraternal twins reared apart and matched twins reared together. The average age of the twins was 59 years. The results demonstrate significant genetic influence on reports of the occurrences of life events, especially for controllable events in which the individual can play an active role. Maximum likelihood model-fitting estimates of genetic influence indicate that 40% of the variance of the total life events score is due to genetic differences among individuals. How genetic factors can affect life experiences and directions for future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

EAS temperaments during the last half of the life span: Twins reared apart and twins reared together.

In this first behavioral genetic study of personality in the last half of the life span, results are reported using the powerful adoption/twin design that compares identical and fraternal twins reared apart and identical and fraternal twins reared together. Traits studied were the EAS temperaments (emotionality, activity level, and sociability), traits that show substantial genetic influence in childhood. It was hypothesized that the EAS traits would also show significant genetic influence later in life and that most of the environmental variation would be nonshared—that is, twins reared together would show no greater resemblance for the EAS traits than twins reared apart. Both hypotheses are supported. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Traits and metatraits: Their reliability, stability, and shared genetic influence.

Metatraits measure individual differences in construct relevancy, whereas traits measure individual differences in construct extremity. 24 traits and metatraits were examined in this study using 157 pairs of identical twins reared together, 95 pairs of identical twins reared apart, 211 pairs of fraternal twins reared together, and 228 pairs of fraternal twins reared apart obtained from the Swedish Adoption/Twin Study of Aging (see N. L. Pedersen et al, 1991). Reliability and stability analyses of the metatraits revealed generally lower reliability and stability across time compared to traits. Quantitative genetic analyses of the relationship between traits and metatraits indicated that approximately 69% of the metatrait's genetic variance is shared with the trait, with 31% of its genetic variance unique to the metatrait. These results suggest that metatraits provide a useful additional view of personality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Importance of shared genes and shared environments for symptoms of depression in older adults.

The Center for Epidemiologic Studies-Depression scale was administered to 68 identical and 161 fraternal twin pairs reared apart and 114 identical and 138 fraternal pairs reared together to ascertain relative genetic and environmental contributions to individual differences in self-reported depressive symptoms. Intraclass correlations and model fitting indicated that genetic influences explained 16% of the variance in the total depression scores and 19% for the Psychomotor Retardation and Somatic Complaints subscale, but heritability was minimal for the Depressed Mood and Well-Being subscales. Influence of family rearing context played a substantial role in explaining twin similarity, whereas unique life experiences accounted for the greatest proportion of variance. Significant age group differences were observed, with heritability greater in twins of 60 years of age or older than in twins under 60, especially for Psychomotor Retardation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nature and nurture: Genetic contributions to measures of the family environment.

Research suggests that measures of the family environment show genetic effects when treated as phenotypes in behavioral genetic analyses. This issue was explored as part of the Nonshared Environment in Adolescent Development project using diverse questionnaire measures of parent–child and sibling interactions. The sample consisted of 707 pairs of siblings (aged 10–18 yrs) in a novel design (identical and fraternal twins and full siblings in nondivorced families, and full, half, and unrelated siblings in stepfamilies). Model-fitting analyses yielded evidence for significant genetic effects for 15 of 18 composite measures. On average, more than a quarter of the variance of these environmental measures can be accounted for by genetic differences among children. These results underline the need to investigate the reactive and active organism–environment transactional processes by which genotypes become phenotypes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Augmentation of therapeutic antitumor immunity by B16F10 melanoma cells transfected by interferon-gamma and allogeneic MHC class I cDNAs

A sample of 66 monozyogtic twins reared apart (MZA) and 51 dizygotic twins reared apart (DZA), and 101 nontwin individuals (mostly spouses of the twins) who participated in the Minnesota Study of Twins Reared Apart (MISTRA) from 1979 to 1995 completed a self-report food frequency questionnaire. Intraclass-correlations and model-fitting analyses indicated that approximately 30% of the variance in the self-report of diet was attributable to genetic factors, with random environmental factors and measurement error responsible for the remaining variance. Spouse correlations were moderate. To investigate the effects of living together during marriage, the absolute differences between husband and wife on the dietary variables with years of marriage were correlated. None of the correlations were significant. Hierarchical multiple regression analyses also indicated that no convergence occurred during marriage. These results suggest that sharing a current family environment exerts minimal influence on individual differences in self-reported diet.     

Heritability of MMPI personality indicators of psychopathology in twins reared apart.

This report presents Minnesota Multiphasic Personality Inventory (MMPI) findings from the Minnesota Study of Twins Reared Apart. Data from 65 unique pairs of monozygotic twins reared apart (MZA) and 54 unique pairs of dizygotic twins reared apart (DZA) were analyzed. As in other results from this sample, MZA twins evidenced substantial similarity, highlighting the influence of shared genes. Biometric modeling yielded estimates of heritability for the MMPI's standard validity and clinical scales and for the Wiggins content scales ranging from .26 to .62 (M?=?.44), echoing previous findings from the twin and adoption literature on personality. The pattern of MZA and DZA correlations suggested nonadditive genetic effects for 3 MMPI scales. Multivariate profile analyses also suggested genetic influence on both profile elevation and shape. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can personality explain genetic influences on life events?

Previous research in the Swedish Adoption/Twin Study of Aging (SATSA) has found genetic influences on life events (R. Plomin et al, see record 1990-14029-001). The present study extends this finding by examining sex differences in genetic and environmental contributions to life events and by examining personality as a mediator of genetic influences on life events in SATSA. Analyses were based on 320 twin pairs, including identical and fraternal twins reared together and apart (mean age 58.6 yrs). Controllable, desirable, and undesirable life events revealed significant genetic variance only for women. There was no significant genetic variance for either sex for uncontrollable events. Multivariate analysis of personality (as indexed by Neuroticism, Extraversion, and Openness to Experience) and life events suggest that all of the genetic variance on controllable, desirable, and undesirable life events for women is common to personality. Thus, in this sample of older adult women, genetic influences on life events appear to be entirely mediated by personality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuroticism, extraversion, and related traits in adult twins reared apart and reared together.

The relative importance of genetic and environmental factors for neuroticism, extraversion, and impulsivity, and monotony avoidance were estimated in a sample of 99 monozygotic and 229 dizygotic pairs of twins reared apart (TRA) and a matched sample of 160 monozygotic and 212 dizygotic pairs of twins reared together (TRT). The average age was 58.6 (SD?=?13.6); 72% of the twins were 50 or older. Model-fitting analyses verified the importance of genetic factors for all four measures; from 23% to 45% of the total variation was attributable to genetic sources. There was considerable evidence that these factors were operating in a nonadditive manner for extraversion and impulsivity. Shared environment accounted for less than 10% of the variance, some evidence for selective placement was found for neuroticism. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Parent ratings of EAS temperaments in twins, full siblings, half siblings, and step siblings.

A twin/family design was used to explore genetic contributions to personality; to evaluate whether twins and nontwins yield different genetic results; and to test for the presence of contrast effects, the tendency of a rater to contrast one sibling with the other, thereby magnifying existing behavioral differences. The sample consisted of 708 adolescent same-sex sibling pairs from 10 to 18 years of age. Pairs included identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins, and full siblings in nondivorced families; and full, half, and unrelated siblings in stepfamilies. Mothers and fathers rated the temperament of their children on the EAS Temperament Survey (A. H. Buss & R. Plomin, 1984). Model-fitting analyses revealed significant genetic infiuences on each of the four EAS dimensions; however, for some dimensions, heritability estimates were significantly greater for twins than for nontwins. Overall, the data were best described by a sibling interaction model, which indicated significant contrast effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genotype€nvironment interaction in personality development: Indentical twins reared apart.

The focus of this study is to identify specific genotype–environment (GE) interactions as they contribute to individual differences in personality in later life. In behavioral genetics, GE interaction refers to the possibility that individuals of different genotypes may respond differently to specific environments. A sample of 99 pairs of identical twins reared apart, whose average age is 59 years, has been studied as part of the Swedish Adoption/Twin Study of Aging (SATSA). Hierarchical multiple regression was used to detect interactions between personality and environmental measures after the main effects of genotype and environment were removed. Analyses yield evidence for 11 significant interactions that provide the first evidence for GE interaction in human development using specific environmental measures. Thus, in addition to the main-effect contributions of heredity and environment, GE interactions contribute to individual differences in personality as measured in the second half of the life course. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parent–child mutuality in early childhood: Two behavioral genetic studies.

Parent–child dyadic mutuality (shared positive affect, responsiveness, and cooperation) is an important component of family socialization processes. This study sought to extend previous research on mutuality by using a quantitative genetic design to examine between- and within-family variations (e.g., sibling differences) and gene-environment processes. The first study included 125 pairs of identical and same-sex fraternal 3-year-old twins. Observations of mutuality and parents' and observers' ratings of family environment and child behavior were gathered. Greater mutuality was associated with higher socioeconomic status. Moderate sibling similarity in parent-child mutuality was accounted for by child genetic similarity, suggesting evocative gene- environment correlation and nonshared environmental processes. These findings were replicated in a 2nd study of 102 pairs of adoptive and biological siblings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heritability of interests: a twin study

The authors administered inventories of vocational and recreational interests and talents to 924 pairs of twins who had been reared together and to 92 pairs separated in infancy and reared apart. Factor analysis of all 291 items yielded 39 identifiable factors and 11 superfactors. The data indicated that about 50% of interests variance (about two thirds of the stable variance) was associated with genetic variation. The authors show that heritability can be conservatively estimated from the within-pair correlations of adult monozygotic twins reared together. Evidence for nonadditive genetic effects on interests may explain why heritability estimates based on family studies are so much lower. The authors propose a model in which precursor traits of aptitude and personality, in part genetically determined, guide the development of interests through the mechanisms of gene-environment correlation and interaction.     

Formal thought disorder in schizophrenics and their twins.

Measured thought disorder in the co-twins of schizophrenic twins in 17 pairs of identical twins, 14 pairs of fraternal same-sex twins, and 12 unpaired twins. Ss were administered a modified version of the Scale for the Assessment of Thought, Language, and Communication Disorders. No evidence of genetic influence on thought disorder was found. A factor analysis of the thought disorder scales revealed 2 interpretable factors reflecting verbosity and discontinuities in the form of speech. Scales with high loadings on the verbosity factor showed signs of familial influence and were significantly correlated with severity of psychiatric history. Scales with high loadings on the discontinuity factor were associated with the florid psychotic phase of illness. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inheritance of general intelligence.

Describes the author's extensive research of the relative influence of hereditary factors on general cognitive ability. Analysis of measures of intelligence for family members related by varying degrees of kinship identified 4 types of factors: common and specific genetic and environmental influences. A model was then developed to represent the mode of mental inheritance, based on the theory of polygenic inheritance of bodily characteristics. The total phenotypic variance was divided into 4 mathematical components, represented by correlations between (a) monozygotic twins reared apart (genetic factor), (b) children and 1 of their parents (dominance factor), (c) fathers and mothers (assortative mating factor), and (d) monozygotic twins reared together and those reared apart (environmental factor). Application of the equation to actual data indicates that intelligence and bodily characteristics are influenced to much the same extent by very similar genetic characteristics. It is concluded that there is a general factor which enters into every type of cognitive process and differs according to the individual's genetic constitution. (40 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does genetic variance for cognitive abilities account for genetic variance in educational achievement and occupational status? A study of twins reared apart and twins reared together

Studies of brothers and twins have shown that about 50 per cent of the variance in educational achievement and 40 per cent of the variance in occupational status reflects between-family variance. About half of the between-family variance for educational achievement and even more for occupational status is due to genetic effects and the remainder is due to sharing the same environment. With data on 35 pairs of male twins reared apart and 56 pairs reared together we investigated the extent to which genetic variance in SES can be attributed to genetic variance for cognitive abilities. For both educational achievement and occupational status there was significant genetic variance both in common with and independent of genetic variance for cognitive abilities. Thus, there are genetic effects contributing to familial similarity for SES that are not the same as those of importance for cognitive abilities. Candidate traits that may account for this remaining genetic variance in SES are personality, interests, or talents not represented in standard cognitive tests.     

Heritability of personality traits in adult male twins

Personality test data from the California Psychological Inventory were collected on 99 pairs of identical and 99 pairs of fraternal adult male twins. Heritabilities were comuted for all 18 scales and compared to the heritabilities for "pure" scales with overlapping items omitted. Two of the pure scales, Responsibility and Femininity, had zero heritabilities, whereas all of the full scales had moderate to high heritabilities. It was concluded that item overlap has contributed significantly to previous failures to find evidence for the differential heritability of personality traits as measured by the CPI. CPI items were classified into genetic or environmental categories and separate factor analyses of items in these categories revealed more differences than similarities in factor structure. The genetic personality factors included Conversational Poise, Compulsiveness, and Social Ease. Environmental factors included Confidence in Leadership, Impulse Control, Philosophical Attitudes, Intellectual Interest, and Exhibitionism. Compared to the genetic factors, each of the environmental factors accounted for only a very small percentage of the variance.     

Twins: Concordance for Piagetian-equivalent items derived from the Bayley Mental Test.

20 test items from the Bayley Mental Scale, which were equivalent to items used in the Piagetian scales developed by S. K. Escalona and H. H. Corman (1967) and by I. C. Uzgiris and J. M. Hunt (1966) were analyzed for evidence of concordance for samples that included at least 120 identical pairs of twins and 85 same-sex fraternal pairs of twins at ages 3, 6, 9, and 12 mo. In addition, within-pair correlations were computed for the total number of Piagetian-equivalent items passed in the 1st yr. Identical twin pairs were found to be consistently more concordant than fraternal twin pairs, the highest levels of significance being found at 3 and 6 mo, and for items related to prehension, object permanence, and imitation. Within-pair correlations for the total score were .80 for identical pairs and .61 for fraternal pairs; these correlations were significantly different. Results support Piaget's assertions regarding the biological origins of sensorimotor capabilities. Expectations for differential utility of infant scales constructed from Piagetian concepts as opposed to other infant measures are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic and Environmental Etiology of Social Behavior in Infancy.

A twin analysis was applied to infants' social behavior in standardized situations that permitted the comparison of social responding to mother and a stranger in different contexts. Ninety-two middle-class children (members of 21 identical twin pairs and 25 same-sex fraternal twin pairs, with an average age of 22.2 months) were observed in their homes using time-sampled observations of specific behaviors in seven situations: (a) a 5-minute warm-up period, (b) approach by stranger, (c) play with stranger, (d) play with mother, (e) cuddling with mother, (f) cuddling with stranger, and (g) separation from mother. Comparisons between intraclass correlations for identical and fraternal twins yielded significant differences for social behavior directed toward the stranger but not toward the mother. In addition, a novel measure of attachment using the difference in social responding toward the mother and stranger suggested heritable influences only in the initial warm-up situation. We conclude that in infancy, heredity affects individual differences in social responding more to unfamiliar persons than to familiar persons. The behavioral-genetic analysis also suggests that the substantial influence of environment in the development of social behavior may occur primarily within families (making members of a family different from one another-including systematic as well as stochastic effects) rather than between families (making family members similar to one another and different from other families), as is widely assumed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)