Genetic and environmental influences on observed personality: Evidence from the German Observational Study of Adult Twins.

Previous behavior-genetic research on adult personality relied primarily on self-reports or peer reports that may be subject to contrast effects, resulting in biased estimates of genetic and environmental influences. In the German Observational Study of Adult Twins (GOSAT), personality traits of 168 monozygotic (MZ) and 132 dizygotic (DZ) twin pairs were rated on 35 adjective scales, largely markers of the Big 5. The ratings were provided by 120 judges who never met the twins but observed videotaped behaviors of 1 twin of each pair in 1 of 15 different settings. The aggregated video-based trait ratings were highly reliable, and substantial correlations were obtained between MZ as well as DZ twins. Model-fit analyses suggested about 40% genetic, 25% shared environmental, and 35% nonshared environmental influence. Extraversion was the only trait that seemed not to be influenced by shared environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A genetic study of maternal and paternal ratings of problem behaviors in 3-year-old twins.

Genetic and environmental influences on problem behaviors were studied in 3-yr-old twins. Fathers' and mothers' ratings of problem behaviors in twins (236 monozygotic [MZ] girls, 210 MZ boys, 238 dizygotic [DZ] girls, 265 DZ boys, and 409 DZ opposite sex pairs) were obtained with the Child Behavior Checklist for Ages 2–3 (T. M. Achenbach, 1992). Twin correlations and results from a model fitting approach showed that genetic, shared environmental, and nonshared environmental influences accounted on average for about 64%, 9%, and 27% of the variance. Although shared environmental influences were small for most scales, they were important for Total Problems and somewhat larger for Externalizing than for Internalizing behaviors. Significant sex differences in genetic and environmental influences and evidence for sibling contrast effects were found for the Overactive scale. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sources of variability in sex-linked personality attributes: A twin study.

31 pairs of monozygotic (MZ) and 28 pairs of dizygotic (DZ) same-sex, adolescent twins completed Spence and Helmreich's Personal Attributes Inventory, which contains separate scales tapping Masculinity (instrumental traits), Femininity (expressive traits), and bipolar Masculinity–Femininity. Sex-adjusted intraclass correlations were computed for the MZ and DZ twin pairs. Significant twin-pair resemblance was found for Masculinity and Femininity, but not for Masculinity–Femininity. MZ resemblance for Masculinity was greater than DZ resemblance, suggesting a genetic component to masculinity development, but no genetic influence was detected in Femininity. All 3 traits showed substantial within-families variability, and it is concluded that future research should give equal attention to nonshared developmental influences that operate to make siblings dissimilar and to shared developmental influences. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Normal personality characteristics in identical twins discordant for schizophrenia.

The authors examined normal personality characteristics of monozygotic (MZ) twins discordant for schizophrenia. Twenty pairs of discordant twins were analyzed; 11 pairs of MZ twins concordant for schizophrenia served as a comparison group. Personality was assessed using the Multidimensional Personality Questionnaire (MPQ; A. Tellegen, 1995). Among discordant twin pairs, twins with schizophrenia were more deviant than normal co-twins on all but 4 of the MPQ's scales. Analysis of MZ twin correlations among the discordant twin pairs revealed substantial erosion of personality similarity as compared to normal individuals, although a cluster of scales related to Constraint/Psychoticism showed significant correlations. The results highlight striking personality divergence related to nonshared environmental influences. It is not possible to determine the point at which the twins diverged, although previous findings from this sample suggest that the observed personality differences may reflect effects of schizophrenia on normal personality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same-age unrelated siblings: A unique test of within-family environmental influences on IQ similarity.

Pairs of unrelated siblings of the same age, reared together from infancy (UST-SA), uniquely replicate the rearing situations of dizygotic (DZ) twins. These dyads offer a new behavioral-genetic design for examining genetic and environmental influences on behavior. An IQ intraclass correlation of .17, based on 21 UST-SAs, is substantially lower than the correlations of .86, .60, and .50 reported for monozygotic (MZ) twins, DZ twins, and siblings, respectively. This finding supports an explanatory model of intelligence that includes genetic factors. The very modest IQ similarity between UST-SAs, despite their common rearing, suggests that the shared environment has a very small effect on intellectual development and supports the position that individuals respond to environments in ways consistent with their genetic predispositions. The results also challenge some critics' views that the behavioral resemblance of MZ twins is primarily a function of shared experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do parents create, or respond to, differences in twins?

In a twin study using direct behavioral observation of parent–child interaction, as well as ratings and experimental measures, the question of the differential treatment by parents of monozygotic (MZ) and dizygotic (DZ) twins was investigated. Data were obtained from 17 MZ and 29 DZ male twin pairs and 44 male singletons, all aged 2? yrs. Four separate approaches, taken together, led to the conclusions that (a) parents do treat MZ twins more alike than DZ twins in some respects; but (b) they do not introduce systematically greater similarity of treatment for MZ twins in actions which they initiate themselves; and (c) the greater homogeneity of treatment of MZ twins, where it occurs, is in line with their actual, rather than their perceived, zygosity. In other words, parents respond to, rather than create, differences between the twins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The development of empathy in twins.

Examined empathy in 94 monozygotic (MZ) and 90 dizygotic (DZ) twin pairs during the 2nd year of life. Children's reactions to simulations of distress in others were videotaped in home and laboratory settings. Some components of concern for others increased with age between 14 and 20 mo for both MZ and DZ twins. Girls scored higher than boys on most of these observational measures. The different components (e.g., emotional concern, prosocial acts, and cognitive exploration) showed substantial coherence and low but significant stability over time. There was modest evidence for heritability of empathy, particularly for the affective component. Maternal reports of prosocial orientations indicated both genetic and environmental influences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heritability of facet-level traits in a cross-cultural twin sample: support for a hierarchical model of personality

The common variance among personality traits can be summarized in the factors of the five-factor model, which are known to be heritable. This study examined heritability of the residual specific variance in facet-level traits from the Revised NEO Personality Inventory. Analyses of raw and residual facet scales across Canadian (183 monozygotic [MZ] and 175 dizogotic [DZ] pairs) and German (435 MZ and 205 DZ pairs) twin samples showed genetic and environmental influences of the same type and magnitude across the 2 samples for most facets. Additive genetic effects accounted for 25% to 65% of the reliable specific variance. Results provide strong support for hierarchical models of personality that posit a large number of narrow traits in addition to a few broader trait factors or domains. Facet-level traits are not simply exemplars of the broad factors they define; they are discrete constructs with their own heritable and thus biological basis.     

Co-occurrence of depressive symptoms and antisocial behavior in adolescence: A common genetic liability.

Recent reviews of research on child and adolescent psychopathology have highlighted the consistently high rates of co-occurring dimensions of psychopathology, particularly between internalizing and externalizing disorders, and have suggested that further research examining the causes of co-occurring syndromes is needed. The authors examined this question in a national sample of 720 same-sex adolescent siblings between 10 and 18 years of age consisting of monozygotic and dizygotic twins, full siblings, half siblings, and unrelated siblings. Composite measures of adolescent and parent reports and observational measures of depressive symptoms and antisocial behavior were subjected to behavioral genetic models that examine the genetic and environmental influences on individual differences in each dimension as well as in the co-occurrence between dimensions. Results indicated that approximately half of the variability in depressive symptoms and antisocial behavior is attributed to genetic factors; shared and nonshared environmental influences were also significant. The co-occurrence of depressive and antisocial symptoms was explained by genetic and shared and nonshared environmental influences. Specifically, approximately 45% of the observed covariation between depressive and antisocial symptoms could be explained by a common genetic liability. Results are interpreted in light of contribution of genetic studies to debates on child and adolescent psychopathology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fetal alcohol syndrome in twins of alcoholic mothers: concordance of diagnosis and IQ

The effects of teratogens can be modified by genetic differences in fetal susceptibility and resistance. Twins of alcoholic mothers provide a unique opportunity to study this phenomenon with respect to alcohol teratogenesis. Sixteen pairs of twins, 5 MZ and 11 DZ, all heavily exposed to alcohol prenatally, were evaluated. They represented all available twins of alcohol-abusing mothers who were on the patient rolls of the authors. The rate of concordance for diagnosis was 5/5 for MZ and 7/11 for DZ twins. In two DZ pairs, one twin had fetal alcohol syndrome (FAS), while the other had fetal alcohol effects (FAE). In 2 other DZ pairs, one twin had no diagnosis while one had FAE. IQ scores were most similar within pairs of MZ twins and least similar within pairs of DZ twins discordant for diagnosis. Despite equivalent alcohol exposure within twin pairs, alcohol teratogenesis appears to be more uniformly expressed in MZ than in DZ twins. These data are interpreted as reflecting the modulating influence of genes in the expression of the teratogenic effects of alcohol.     

Auditory lateralization in monozygotic twins

In an attempt to investigate whether auditory lateralization has a heritable component, 20 monozygotic (MZ) twin pairs were examined with four different dichotic listening tests known to produce reliable right-ear advantages (REAs) in right-handers. Ten twin pairs were concordantly right-handed (MZ-RR), and ten twin pairs were discordant for handedness (MZ-RL). Intraclass correlations for MZ twin pairs were weak or nonexistent for ear advantage, but relatively strong for overall correct scores and mean reaction times, measures unrelated to laterality scores. These results support the hypothesis that auditory lateralization, as measured with dichotic tests, is nongenetic in origin. A comparison of MZ twins and right-handed siblings (n = 20) showed that right-handed siblings exhibited strong REAs, whereas left-handed siblings (n = 20) and MZ twins showed weak or absent REAs, indicating that twins may be atypically lateralized with respect to auditory lateralization.     

The role of aggressive personality and family relationships in explaining family conflict.

This study investigated whether genetic and environmental influences on global family conflict are explained by parents' personality, marital quality, and negative parenting. The sample comprised 876 same-sex pairs of twins, their spouses, and one adolescent child per twin from the Twin and Offspring Study in Sweden. Genetic influences on aggressive personality were correlated with genetic influences on global family conflict. Nonshared environmental influences on marital quality and negative parenting were correlated with nonshared environmental influences on global family conflict. Results suggest that parents' personality and unique experiences within their family relationships are important for understanding genetic and environmental influences on global conflict in the home. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Landscape ecology and epidemiology of vector-borne diseases: tools for spatial analysis

We studied twins to examine the genetics of epilepsy syndromes. We ascertained 358 twin pairs in whom one or both reported seizures. After evaluation, 253 of 358 (71%) had seizure disorders and 105 pairs were false positives. Among the monozygous (MZ) pairs, more were concordant for seizures (48 of 108; casewise concordance = 0.62 +/- 0.05) than among the dizygous (DZ) pairs (14 of 145; casewise concordance = 0.18 +/- 0.04). In 94% of concordant MZ pairs, and 71% of concordant DZ pairs, both twins had the same major epilepsy syndrome. When analyzed according to major epilepsy syndrome, the casewise concordances for generalized epilepsies (MZ = 0.82; DZ = 0.26), both idiopathic (MZ = 0.76; DZ = 0.33) and symptomatic (MZ = 0.83; DZ = 0), were greater than those for partial epilepsies (MZ = 0.36; DZ = 0.05), with intermediate values seen for febrile seizures (MZ = 0.58; DZ = 0.14) and unclassified epilepsies (MZ = 0.53; DZ = 0.18). We conclude that genetic factors are particularly important in the generalized epilepsies but also play a role in the partial epilepsies. The high frequency of concordant MZ pairs with the same major syndrome strongly suggests there are syndrome-specific genetic determinants rather than a broad genetic predisposition to seizures.     

Genetic and environmental factors in relative body weight and human adiposity

We review the literature on the familial resemblance of body mass index (BMI) and other adiposity measures and find strikingly convergent results for a variety of relationships. Results from twin studies suggest that genetic factors explain 50 to 90% of the variance in BMI. Family studies generally report estimates of parent-offspring and sibling correlations in agreement with heritabilities of 20 to 80%. Data from adoption studies are consistent with genetic factors accounting for 20 to 60% of the variation in BMI. Based on data from more than 25,000 twin pairs and 50,000 biological and adoptive family members, the weighted mean correlations are .74 for MZ twins, .32 for DZ twins, .25 for siblings, .19 for parent-offspring pairs, .06 for adoptive relatives, and .12 for spouses. Advantages and disadvantages of twin, family, and adoption studies are reviewed. Data from the Virginia 30,000, including twins and their parents, siblings, spouses, and children, were analyzed using a structural equation model (Stealth) which estimates additive and dominance genetic variance, cultural transmission, assortative mating, nonparental shared environment, and special twin and MZ twin environmental variance. Genetic factors explained 67% of the variance in males and females, of which half is due to dominance. A small proportion of the genetic variance was attributed to the consequences of assortative mating. The remainder of the variance is accounted for by unique environmental factors, of which 7% is correlated across twins. No evidence was found for a special MZ twin environment, thereby supporting the equal environment assumption. These results are consistent with other studies in suggesting that genetic factors play a significant role in the causes of individual differences in relative body weight and human adiposity.     

Environmental and genetic influences on dimensions of perceived parenting: A twin study.

Investigated determinants of E. S. Schaefer's (see record 1965-12269-001) 3 dimensions of perceived parenting by administering a shortened Children's Reports of Parental Behavior Inventory to 46 pairs of identical twins and 43 pairs of fraternal twins (mean age 17 yrs) residing with their natural parents. There were neither sex main effects nor Sex?×?Zygosity interactions. Although a significant difference between monozygotic (MZ) and dizygotic (DZ) correlations was observed for Acceptance vs Rejection (A–R), a test of the equal environments assumption showed that it was violated for this dimension. Unequal environments had a greater effect on perceptions of maternal A–R than on paternal A–R. MZ and DZ correlations for 2 other parenting dimensions, Firm vs Lax Control and Psychological Control vs Autonomy, were about equal and significant. Thus, with a possible exception of paternal A–R, environmental influences appear to be responsible for Ss' resemblance in perceptions of parenting behaviors. (15 ref) (PsycINFO Database Record (c) 2010 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)     

The structure of self-concept in female preadolescent twins: a behavioral genetic approach

Two hundred and forty-three female monozygotic (MZ) and 164 female dizygotic (DZ) twin pairs, aged 11 and 12 years, who participated in the ongoing Minnesota Twin Family Study, completed six specific scales of the Piers-Harris Children's Self-Concept Scale (P-H). Model-fitting analyses yielded three major conclusions. First, approximately 30% of the variance in specific self-concepts in female preadolescents was due to genetic factors, with the remaining variance being accounted for primarily by nonshared environmental factors and measurement error. Second, the underlying common genetic, shared environmental, and nonshared environmental factors influenced specific facets of self-concept directly and independently, rather than through an intervening phenotypic general self-concept. Finally, whereas genetic, shared environmental, and nonshared environmental factors were necessary to explain the commonality among the specific self-concept scales, only genetic and nonshared environmental factors were sufficient to explain the specificity of those scales.     

Cadmium suppresses apoptosis induced by chromium

Influence of intrapair differences in birth weight (IDBW) on the patterns of postnatal growth of MZ and DZ twins from middle/late childhood to adolescence were studied in 49 MZ, 40 DZ male and 40 MZ, 35 DZ female pairs coming from the Wroc?aw Longitudinal Twins Study. Intrapair differences in the patterns in postnatal growth were expressed in several indices: average differences in standardized values (ASD Height, ASD Weight); absolute average differences in standardized values (ABSD Height, ABSD Weight); average Euclidean distances coefficient (EUCD Height, EUCD Weight); coefficient of shape differences (SHC Height, SHC Weight); measure of deviation (MD Height, MD Weight) and correlation coefficient for the standardized attained values (CORC Height, CORC Weight). Relationships between IDBW and indices were based on the means of Spearman Rank Order Correlation. Additionally for 40 MZ, 35 DZ male and 25 MZ, 18 DZ female pairs, the relationships between IDBW and intrapair differences in biological parameters derived from Preece Baines model 1, describing differences in time (DT1), height (DH1), velocity (DV1) at the beginning of the adolescent growth spurt, differences in time (DT2), height (DH2), velocity (DV2) at peak height velocity and differences in adult height (DAH) were examined. The results showed that only in MZ girls did dissimilarity in birth weights significantly impair the subsequent growth in stature. Furthermore, the results revealed that birth weight influences the parameter describing adult stature in MZ girls. It is concluded that the lack of relationship in DZ twins is due to their unique genotype, which strongly determines the postnatal growth. Three possible interpretations are given as explanations of the results obtained in this study: male excess neonates mortality, 'third factor' and programmed of growth in utero.     

Lung function in Indian twin children: comparison of genetic versus environmental influence

The relative contributions of genetic and environmental components in the variability of lung function measurements were studied in 54 twin pairs. Thirty pairs of monozygote (MZ) twins and 24 pairs of dizygotic (DZ) twins were examined. All measurements were made with 9-litre closed-circuit-type expirographs using standard spirometric techniques, except for peak expiratory flow rate (PFER) which was recorded with a Wright peak flow meter. Within-pair variances for inspiratory capacity (IC), vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), forced mid-expiratory flow (FEV25-75%), forced end-expiratory flow (FEF75-85%), maximum expiratory flow (FEF200-1200ml), forced maximum voluntary ventilation MVVF) and PEFR were significantly smaller (p < 0.01) in MZ twins than in DZ twins. Tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), forced expiratory volume in 1 second as a percentage of forced vital capacity (FEV1%), and forced expiratory time (FET) were not significantly different. Within-pair correlations were all higher in MZ than DZ twins. All measurements except for VT and PEFR showed high levels of heritability (23-99%). All measurements were positively and significantly correlated with physical characteristics such as weight, standing height, surface area, arm-span, chest circumference and age, except FEV1% and FET. Residual values adjusted for physical characteristics showed similar results to unadjusted values in most cases. These data indicate that major lung function measurements are possibly influenced more by genetic than environmental factors. Genetically influenced measurements show higher levels of heritability estimates and suggest that genetic determination of lung function is possibly independent of the influence of physical characteristics.