Environmental predictors of personality differences: A twin and sibling study.

Nonshared environmental influences have consistently been shown to account for at least as much of the variance in personality as genetic factors, but the nature of these nonshared influences has largely remained unidentified. To identify environmental predictors of differential personality development, the Personality Research Form and 4 measures of people's perceptions of their background environments were administered to 143 adult twin pairs (93 monozygotic [MZ] and 50 dizygotic [DZ]) and 66 pairs of same-sex nontwin (NT) siblings. Differences between MZ twins, DZ twins, and NT siblings in a number of dimensions of personality were significantly related to differences on the environmental measures, and phenotypic correlations between the personality and environment measures were themselves entirely attributable to correlated nonshared environmental effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

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)     

Sex differences in genetic and environmental influences on DSM–III–R attention-deficit/hyperactivity disorder.

Approximately 5% of children are affected by attention-deficit/hyperactivity disorder (ADHD), and more boys are affected than girls. This study examined the magnitude of genetic and environmental influences on ADHD and several questions regarding sex differences in its prevalence and liability. The participants were 2,391 twin and sibling pairs from Australia, ages 3–18. ADHD symptoms in the general population were highly heritable (h2?=?.85–.90), as were deviant ADHD scores in the selected population. The magnitude of familial influences was similar for boys and girls, although there were shared environmental influences on ADHD in girls but not boys and dominance genetic influences on ADHD in boys but not girls. Specific genetic and environmental influences were highly similar for boys and girls. Evidence supported the polygenic multiple threshold model rather than the constitutional variability model of sex differences in ADHD. (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)     

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)     

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)     

Determinants of plasma levels of plasminogen activator inhibitor-1 : A study of normotensive twins

We investigated whether plasma levels of the plasminogen activator inhibitor type 1 antigen (PAI-1:Ag) are genetically determined in monozygotic (MZ) and dizygotic (DZ) twins. Twenty-five pairs of healthy twins underwent measurements of PAI-1:Ag and other variables, including body mass index, mean blood pressure, plasma renin activity, insulin, and glucose. To ascertain the zygosity of twins, highly discriminating micro- and minisatellite systems with variable numbers of tandem repeats were analyzed by PCR amplification followed by polyacrylamide gel electrophoresis. Subjects were also genotyped for the 4G/5G polymorphism by PCR. Estimates of genetic variance and heritability were obtained for PAI-1:Ag, and for body mass index, mean blood pressure, plasma renin activity, glucose, and insulin by jointly examining data in a path analysis with TWINAN90. Results showed that 12 pairs of twins were MZ and 13 were DZ. All tests of genetic variance [within pair (WP): F=6.24, P=0.002; among component (AC): F=2.62, P=0.04; average absolute difference t test=3. 00, P=0.004] showed significant genetic variance of PAI-1:Ag, but not of the other variables. Three tests of heritability (WP=0.837, P=0.002; AC=1.791, P<0.05; intraclass correlation: 1.180, P=0.001) consistently showed significant PAI-1:Ag heritability. Additive genetic influences (A), dominance genetic effect (D), and random environmental influences (E) accounted for 0.714, 0.154, and 0.132 of PAI-1:Ag variance, respectively. No effect of different 4G/5G genotypes was found. Thus, these results show significant genetic variance and heritability of PAI-1:Ag and suggest that A is more important than both D and E in determining PAI-1:Ag variance.     

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.     

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.     

Age differences in genetic and environmental influences on eating attitudes and behaviors in preadolescent and adolescent female twins.

A sample of 680 11- and 602 17-year-old female twins was used to examine (a) age differences in genetic and environmental influences on disordered eating attitudes and behaviors and (b) associations between body mass index (BMI) and eating attitudes and behaviors. Univariate, biometrical model-fitting analyses indicated that 11-year-old twins exhibited less genetic and greater shared environmental influence on eating attitudes and behaviors than 17-year-old twins. Bivariate model-fitting analyses indicated that the relationship between BMI and eating attitudes was mediated primarily by common shared environmental influences in 11-year-old twins and common genetic influences in 17-year-old twins. Nonetheless, the majority of genetic influences on eating attitudes and behaviors in older twins were due to genetic effects that are independent of those operating in BMI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Dental caries and treatment characteristics in human twins reared apart

The 'reared apart' model, eliminating the effect of common environmental factors, is used extensively in twins research. In this study, teeth present (TP), teeth present excluding third molars (TPX3), teeth restored (TR), teeth restored index (TRI), surfaces restored (SR), surfaces restored index (SRI) and surfaces restored or carious (SRCI), were compared in 46 monozygotic (MZ) twin pairs and 22 dizygotic (DZ) twin pairs separated during infancy and raised apart. The dental examination included charting, panoral and bitewing radiographs, study models and a questionnaire. Data were analysed using intraclass correlations (ICC) and analysis of variance (corrected for age and sex). For all characteristics, the MZ pairs showed greater within-pair similarity than DZ pairs. For MZ pairs, the ICC values for the dental characteristics were all statistically significant (p < 0.005): TP, 0.45; TPX3, 0.49; TR, 0.57; TRI, 0.61; SR, 0.46; SRI, 0.67; SRCI, 0.58. For DZ pairs, none of the ICC values reached statistical significance: TP, 0.04; TPX3, 0.11; TR, 0.30; TRI, 0.31; SR, 0.20; SRI, 0.17; SRCI, 0.26. Despite subjects being reared in different environments, receiving different diets and different dental professional care, the MZ findings demonstrated significant genetic variance (45-67%) for the number of teeth present, number of teeth and surfaces restored, and caries present; the DZ data supported this conclusion. These findings provide new evidence for a genetic contribution to dental caries.     

A study of genetic and environmental effects on the co-occurrence of problem behaviors in three-year-old-twins.

The authors examined the genetic and environmental causes of the co-occurrence of problem behaviors in children. The analyses involved mother and father ratings of Oppositional, Withdrawn/Depressed, Aggressive, Anxious, Overactive, and Sleep Problems in 446 monozygotic and 912 dizygotic pairs of 3-year-old twins. Genetic factors contributed on average .150 (37.3%), shared environment .206 (51.2%), and nonshared environment .046 (11.4%) to the phenotypic correlations between the syndromes. Genetic and environmental factors caused different groupings. Internalizing and Externalizing groupings were indicative of nonshared environmental factors; clusters of problem behaviors with either the Aggressive or Anxious symptoms were most suggestive of genetic factors, and high scores on all syndromes indicated shared environmental influences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Genetic and environmental contributions to the association between quantitative ultrasound and bone mineral density measurements: a twin study

This study was designed to assess the relative contributions of genetic and environmental factors to the variation and covariation of quantitative ultrasound (QUS) measurements and their relationships to bone mineral density (BMD). Forty-nine monozygotic (MZ) and 44 dizygotic (DZ) female twins between 20 and 83 years of age (53 +/- 13 years, mean +/- SD) were studied. Digital (phalangeal) QUS (speed of sound [SOS]) and calcaneal QUS (broadband ultrasound attenuation [BUA] and velocity of sound [VOS]) were measured using a DBM Sonic 1200 ultrasound densitometer and a CUBA ultrasound densitometer, respectively. Femoral neck (FN), lumbar spine (LS), and total body (TB) BMD were measured using dual-energy X-ray absorptiometry. Familial resemblance and hence heritability (proportion of variance of a trait attributable to genetic factors) were assessed by analysis of variance, univariate, and multivariate model-fitting genetic analyses. In both QUS and BMD parameters, MZ twins were more alike than DZ pairs. Estimates of heritability for age- and weight-adjusted BUA, VOS, and SOS were 0.74, 0.55, and 0.82, respectively. Corresponding indices of heritability for LS, FN, and TB BMD were 0.79, 0.77, and 0.82, respectively. In cross-sectional analysis, both BUA and SOS, but not VOS, were independently associated with BMD measurements. However, analysis based on intrapair differences suggested that only BUA was related to BMD. Bivariate genetic analysis indicated that the genetic correlations between BUA and BMD ranged between 0.43 and 0.51 (p < 0.001), whereas the environmental correlations ranged between 0.20 and 0.28 (p < 0.01). While the genetic correlations within QUS and BMD measurements were significant, factor analysis indicates that common genes affect BMD at different sites. Also, individual QUS measurements appear to be influenced by some common sets of genes rather than by environmental factors. Significant environmental correlations were only found for BMD measurements and ranged between 0.50 and 0.65 (p < 0.001). These data suggest that QUS and BMD measurements are highly heritable traits. While it appears that there is a common set of genes influencing both QUS and BMD measurements, specific genes yet to be identified appear to have greater effects than that of shared genes in each trait.     

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.     

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.     

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)