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.     

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)     

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)     

Parkinson disease in twins: an etiologic study

CONTEXT: The cause of Parkinson disease (PD) is unknown. Genetic linkages have been identified in families with PD, but whether most PD is inherited has not been determined. OBJECTIVE: To assess genetic inheritance of PD by studying monozygotic (MZ) and dizygotic (DZ) twin pairs. DESIGN: Twin study comparing concordance rates of PD in MZ and DZ twin pairs. SETTING AND PARTICIPANTS: A total of 19842 white male twins enrolled in the National Academy of Sciences/National Research Council World War II Veteran Twins Registry were screened for PD and standard diagnostic criteria for PD were applied. Zygosity was determined by polymerase chain reaction or questionnaire. MAIN OUTCOME MEASURE: Parkinson disease concordance in twin pairs, stratified by zygosity and age at diagnosis. RESULTS: Of 268 twins with suspected parkinsonism and 250 presumed unaffected twin brothers, 193 twins with PD were identified (concordance-adjusted prevalence, 8.67/1000). In 71 MZ and 90 DZ pairs with complete diagnoses, pairwise concordance was similar (0.129 overall, 0.155 MZ, 0.111 DZ; relative risk, 1.39; 95% confidence interval, 0.63-3.1). In 16 pairs with diagnosis at or before age 50 years in at least 1 twin, MZ concordance was 1.0 (4 pairs), and DZ was 0.167 (relative risk, 6.0; 95% confidence interval, 1.69-21.26). CONCLUSIONS: The similarity in concordance overall indicates that genetic factors do not play a major role in causing typical PD. No genetic component is evident when the disease begins after age 50 years. However, genetic factors appear to be important when disease begins at or before age 50 years.     

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)     

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)     

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.     

Comment on Berenbaum, Oltmanns, and Gottesman (1985): "Formal thought disorder in schizophrenics and their twins."

Berenbaum, Oltmanns, and Gottesman (1985) reported no significant difference in the concordance for monozygotic (MZ) and dizygotic (DZ) schizophrenic twins in measures of thought disorder. They therefore concluded that thought disorder is not genetically transmitted. Although their data do not provide evidence in favor of genetic transmission, their negative conclusion is weakened because (a) they did not assess mild instances of thought disorder typically seen in nonpsychotic persons and because (b) comparison of MZ and DZ concordances may not be a sufficiently powerful test to detect genetic influences on traits that both contribute to the risk for a disease and reflect the severity of the disease once established. (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)     

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.     

Twin imitation for antisocial behavior: Implications for genetic and family environment research.

When twin pairs influence each other's behavior, observed variance is greater for monozygotic (MZ) twins than for dizygotic (DZ) twins under at least 1 of 2 conditions: (1) The trait has some heritability, and (2) MZ twins influence each other more than do DZ twins. Applied to a trait that has an underlying continuous distribution but is measured as a dichotomy, the presence of reciprocal twin influence predicts that if the base rate for the trait is not exactly 50%, then the prevalence of the trait should differ in MZ and DZ twin pairs. This prediction held for registered criminality in a large twin cohort. Methods of analysis that permit reciprocal twin interaction not only provide better statistical fits to the data but also yield estimates of heritability that agree with adoption data. Results suggest that the genetic influence on registered criminality may be more modest than previously thought. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Manual performance and laterality in twins of known chorion type

Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8-12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used; dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.     

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.     

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)     

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.     

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.