The treatment of advanced ovarian carcinoma with high dose, intravenous cyclophosphamide

The equal environments hypothesis of twin methodology was examined for the variable of similarity of appearance as it affects the personality ratings of young twins. There were two separate samples, the first with 95 pairs of same-sex twins and the second with 111 pairs. The average age of the twins in both samples was 3-1/2 years. Mothers rated their twins on four personality traits and on confusability of appearance. Not surprisingly, identical twins were markedly more similar in appearance than fraternal twins. The effect of this inequality on the personality ratings of the two types of twins was examined by correlating ratings of similarity of appearance with the absolute difference on the four personality traits for each pair of twins. None of the correlations was significant for the identical twins, suggesting that greater resemblance in appearance in identical twins does not make them more similar in personality. Indeed, the data suggested a contrast effect in which identical twins who were easily mistaken in appearance tended to be rated as less similar in personality. Thus, although similarity of appearance may create unequal environments for the two types of twins, it does not appear to bias twin studies in the direction of inflated heritabilities, at least for rating studies of the personality of young twins.     

A twin study of mathematics disability

Although results obtained from recent twin and adoption studies suggest that individual differences in mathematics performance are due in part to heritable influences, no genetic analysis of mathematics disability (MD) has been previously reported. In this article we present data from the first twin sample ascertained for mathematics deficits (40 identical and 23 same-sex fraternal twin pairs in which at least one member had MD). When mathematics performance data from these twin pairs were subjected to a multiple regression analysis, evidence for a significant genetic etiology was obtained. However, tests for the differential etiology of MD as a function of reading performance level were nonsignificant. Results of this first twin study of MD indicate that the condition is significantly heritable, but data from additional twin pairs will be required to test hypotheses of differential etiology more rigorously.     

Substantial genetic influence on cognitive abilities in twins 80 or more years old

General and specific cognitive abilities were studied in intact Swedish same-sex twin pairs 80 or more years old for whom neither twin had major cognitive, sensory, or motor impairment. Resemblance for 110 identical twin pairs significantly exceeded resemblance for 130 fraternal same-sex twin pairs for all abilities. Maximum-likelihood model-fitting estimates of heritability were 62 percent for general cognitive ability, 55 percent for verbal ability, 32 percent for spatial ability, 62 percent for speed of processing, and 52 percent for memory. There was also evidence for the significant influence of idiosyncratic experience as the environmental component that most determines individual differences in cognitive abilities late in life.     

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)     

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)     

Altruism and aggression: The heritability of individual differences.

Administered 5 questionnaires measuring altruistic and aggressive tendencies to 573 adult twin pairs (mean age about 30 yrs) of both sexes from the University of London Institute of Psychiatry Volunteer Twin Register. Ss included 206 monozygotic (MZ) female, 90 MZ male, 133 dizygotic (DZ) female, 46 DZ male, and 98 DZ opposite-sex pairs. The questionnaires measured altruism, empathy, nurturance, aggressiveness, and assertiveness. The intraclass correlations for the 5 scales, respectively, were .53, .54, .49, .40, and .52 for the 296 MZ pairs, and .25, .20, .14, .04, and .20 for the 179 same-sex DZ pairs, resulting in broad heritability estimates of 56, 68, 70, 72, and 64%. Additional analyses, using maximum-likelihood model-fitting, revealed approximately 50% of the variance on each scale to be associated with genetic effects, virtually 0% with the twins' common environment, and the remaining 50% with each twins' specific environment and/or error associated with the test. Correcting for the unreliability in the tests raised the maximum-likelihood heritabilities to approximately 60%. Age and sex differences were also found: Altruism increased over the age span from 19 to 60 yrs, whereas aggressiveness decreased; at each age, women had higher scores than men on altruism and lower scores on aggressiveness. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genes and environment have gender-independent influences on the eating and drinking of free-living humans

Males and females differ in the amounts of food and fluids they ingest. Previous studies suggest that this may be due to differences in genetic influences on intake. Gender differences in the heritability of food and fluid intake were investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day food intake diaries. Linear structural modeling revealed significant genetic influences on the overall and meal intakes of foods and fluids and specific beverage and food types. No gender differences were found in the genes that influence intake or, for the most part, in the magnitude of the genetic influences on intake. However, gender differences were found for the between-meal intakes of fluids, being influenced by heredity for males but by common, familial, environment for females. The data suggest that intakes are equivalently influenced by inheritance and individual environment for both males and females and that most gender differences are due to a simple multiplicative difference between intakes possibly due to body size and/or caloric expenditure differences.     

Multivariate behavioral genetic analysis of achievement and cognitive measures in reading-disabled and control twin pairs

In recent years behavioral genetic studies have provided conclusive evidence that reading disability and related learning disorders, such as mathematics disability, are due at least in part to heritable factors (DeFries et al. 1987; Alarcón et al. 1997). Although the observed relationship between performance in these areas also may be due substantially to genetic influences (Light and DeFries 1995; Thompson et al. 1991), relatively few studies have examined the genetic and environmental etiology of this covariation in a multivariate framework. In the present study data from 196 identical (monozygotic; MZ) and 155 same-sex fraternal (dizygotic; DZ) twin pairs in which at least one member of each pair evidenced reading problems in school (reading disabled) were subjected to a multivariate behavioral genetic analysis. Structural equation models were fitted to twin data for verbal IQ (VIQ), phonological decoding ability (PHON), reading performance (READ), and mathematics performance (MATH) to assess the extent to which VIQ and PHON mediate the observed covariation between READ and MATH. Results suggest that VIQ and PHON account for most of the covariation between READ and MATH. Moreover, approximately 82% of the observed correlation between READ and MATH was due to genetic factors that also influence VIQ and PHON. When data from 132 MZ and 91 same-sex DZ control twin pairs in which neither twin had a history of reading problems were subjected to the same analyses, the covariation between READ and MATH was found to be due to both genetic and shared environmental influences. Thus genetic factors that influence VIQ and PHON also contribute to the observed covariation between READ and MATH in both a reading-disabled and a control twin sample.     

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)     

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)     

Hereditary influences on vocational preferences as shown by scores of twins on the Minnesota Vocational Interest Inventory.

The Minnesota Vocational Interest Inventory (MVII) scores of 53 fraternal pairs of twins showed greater within-pair variances than did the scores of 71 identical pairs. For 9 of the scores and 4 of the area keys the F test showed a statistically significant increase in within-pair variance for the fraternal twins. This is interpreted as evidence for a hereditary component in interests in occupations requiring no scientific ability. The hereditary influence operates probably through personality variables. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familial resemblance in infant mental development.

Compared the scores on a scale of mental development (N. Bayley) of 151 sets of 8-mo-old twins and 2,481 other sibling pairs in the Collaborative Perinatal Project. Intraclass correlation coefficients between scores of twins were high (.84, monozygotic; .55, dizygotic), suggesting a substantial genetic influence; however, the average correlation between scores of other siblings was only .22. The discrepancy between the values for dizygotic twins and other sibling pairs may have resulted from the twins' greater environmental similarity. The high heritability estimate derived from the difference between monozygotic and dizygotic correlations was due to the higher concordance for severe retardation in monozygotic pairs. It is noted that since infant twins are a unique sample in terms of retardation frequency as well as birth weight and gestational age, it may be inappropriate to generalize infant twin study results to singleton populations. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The heritability of inhibited and uninhibited behavior: A twin study.

Young children who respond to the unfamiliar with wariness and avoidance belong to a temperamental category called behaviorally inhibited; sociable children who approach the unfamiliar are called uninhibited. This study assessed the heritable nature of these 2 categories. The longitudinal sample consisted of 178 same-sex twin pairs seen at 14 mo and 162 pairs seen at 20 and 24 mo. An aggregate inhibition index was constructed at each of the 3 ages by averaging standard scores for observed laboratory behaviors indicative of wariness. The index had relatively high internal consistency at all ages. Analyses of data from selected twin pairs suggest that extremely inhibited behaviors are heritable. Results of longitudinal genetic correlation analyses provide evidence for substantial genetic contributions to continuity and change from 14 to 24 mo. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The origins of individual differences in adjective check list scores.

Genetic and environmental contributions to individual differences in Adjective Check List (ACL) scores were estimated in a study of 61 pairs of identical (MZ) and fraternal (DZ) twin girls of grade-school age. Comparisons of the intraclass correlation coefficients of MZ and DZ groups for each of the ACL scales showed genetic contributions to 9 scales and systematic environmental contributions to 7 scales. The proportions of genetic and environmental variance are discussed in the context of other research findings, and the problems of scale validity in this population are examined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental stability of the relative influence of genes and environment on specific cognitive abilities during childhood.

Describes hierarchical multiple regression (HMR) model for analysis of cross-sectional data to examine developmental changes in the relative influence of genes and environment. The HMR model is advocated because it provides a test of significance for age changes without the loss of information and statistical power that results when continuous variables, such as age, are assigned to categories. This model was applied to 9 tests of specific cognitive abilities that were administered to 54 identical and 33 same-sex fraternal twin pairs whose ages ranged from 5 to 11 yrs. Results indicate that familial influences as well as the relative mixture of genetic and environmental influences on specific cognitive abilities remain stable during this fast-moving developmental era. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Friendship pair similarity as a measure of group value.

To investigate the extent members of social groups assort along dimensions valued by the group, the authors studied similarity among naturally occurring same-sex, same-race pairs on 3 university campuses. Each member of a pair was asked about height, weight, age, politics, and exercise. The authors hypothesized that people form friendships along the dimensions that they value and that these dimensions of value represent the "fault lines" around which the larger social group of which they are members divides itself. Women assort more on physical characteristics than men, reflecting the social value of women's physical appearance. Men are more likely to assort by activity than women, reflecting men's activity-based identities. Low levels of similarity were found among friendship pairs for Black participants at a predominantly White campus but high levels were found at a predominantly Black campus. Group similarity assortment is discussed as a subtle measure of group values and opportunity, based on the composition of the social ecological setting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Health locus of control in late life: A study of genetic and environmental influences in twins aged 80 years and older.

The factor structure of health locus of control (Form A; K. A. Wallston, B. S. Wallston, & R. DeVellis, 1978) was examined in 420 octogenarians (M age?=?83.2 years), and the contributions of genetic and environmental factors to health-control beliefs in 141 octogenarian twin pairs (71 identical, 70 same-sex fraternal) were estimated. Factor analyses reproduced previously proposed factors (Internal, Chance, and Powerful Others). Associations between health-control beliefs and life satisfaction, depression, and other health-related measures (e.g., self-rated health, outpatient contacts, and hospitalization), were modest. Quantitative genetic analyses revealed significant shared environmental influence on the Chance subscale, and significant familiarity (attributable to a combination of genetic and shared environmental influences) on the Powerful Others subscale; there was no evidence of familiarity on the Internal subscale. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children's methods of coping with stress: a twin study of genetic and environmental influences

The relative importance of environmental and hereditary factors in how children cope with stress was examined. Emotion-focused, problem-focused, and additional coping variables were assessed in 44 monozygotic (MZ) and 30 dizygotic (DZ) twin pairs, aged 9-16 years. The effects of heritability, shared environment, and unshared environment were examined in structural modelling analyses. Genetic factors accounted for a majority of the reliable variance in four of seven coping variables, while effects of twins' shared environment were negligible for all but one coping variable. Environmental factors important to individual differences in coping strategies were primarily unique to each child (unshared between the twins), highlighting the importance of individual experiences in shaping coping behaviors.