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)     

Risk and resilience in early mental development.

Examined mental development scores for 2 groups of at-risk twins throughout their childhood, those classified as small for gestational age (SGA), and those twins falling below 1,750 g birthweight. The Ss were recruited as newborns—about 30 new pairs were added each year—and the total sample included 450 pairs of twins. Ss were assessed using the Bayley Scales of Infant Development at age 24 mo and the WPPSI at age 6 yrs. Results show that the SGA Ss showed only a modest deficit in IQ scores as compared to the full twin Ss, and thus these small-for-date Ss did not appear to be at special risk. The Ss below 1,750 g, however, did show a very significant deficit in IQ scores throughout childhood. When the recovery patterns were examined for this group, upper SES Ss appeared to recover completely, whereas lower SES Ss remained significantly depressed. Mother's education was significantly related to recovery from 24 mo onward, which suggests that maternal intelligence plays a prominent role in determining the level of recovery. When monozygotic Ss of markedly unequal birth weight were compared, the twins who weighed less than 1,750 g attained the same level of IQ scores at 6 yrs as did their heavier co-twins. Among these genetic replicates, the initially powerful effects of low birth weight did not exert a long-term handicapping effect on mental development. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Stroop Color-Word Test: Genetic and environmental influences; Reading, mental ability, and personality correlates.

Using a relatively large adult sample (271 participants in the Minnesota Study of Twins Reared Apart, including 50 pairs of monozygotic and 37 pairs of dizygotic twins), the authors evaluated prior findings of reading, mental ability, and personality correlates of Stroop Color-Word Test (SCWT; J. R. Stroop, 1935) scores. The twin sample allowed the authors to estimate genetic and environmental influences associated with the SCWT scores. No meaningful personality correlates were detected. Genetic influences ranged from 35% for the Interference effect to 53% for the Word score. In spite of significant correlations between the SCWT scores and selected measures of mental ability, genetic influence on SCWT scores was relatively unaffected when the influences of correlated ability measures were removed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Twins: Patterns of cognitive development as measured on the Wechsler Preschool and Primary Scale of Intelligence.

Appraised cognitive patterning and development for 142 pairs of twins at 4, 5, and 6 yrs of age, based on their test scores on the Wechsler Preschool and Primary Scale of Intelligence. Compared with the singleton norms, the twins showed an initial lag at age 4, with Verbal IQ being somewhat more depressed than Performance IQ. By age 6, however, the twins had fully recovered their deficit on both scales and reached parity with singletons. Monozygotic twins displayed relatively high within-pair correlations for Verbal IQ and Performance IQ, and even higher correlations for Full Scale IQ. Dizygotic twins displayed moderate within-pair correlations for the IQ scores, and most were significantly lower than the monozygotic correlations. Further analysis showed that monozygotic twins were also significantly more concordant for the differences between Verbal IQ and Performance IQ, and for the patterning of the subtest scores. Measures of family socioeconomic status and parental education correlated .28-.32 with the twins' IQ at age 6. Results suggest that within a broad range of home environments, the genetic blueprint made a substantial contribution to cognitive patterning and development. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic association between atopy and behavioral symptoms in middle childhood

The relationship of atopic and behavioral symptoms in a community sample of 66 monozygotic and 141 dizygotic twin pairs, ages 4-11 years, was investigated via mother report questionnaires. Within-person correlation between atopic symptoms and Child Behavior Checklist internalizing symptoms (CBCL-INT) was .21 (p < .001) for the total sample. Cross-correlations between atopy and CBCL-INT were .26 for monozygotic and .04 for dizygotic twins. A common and specific factor model applied to the data revealed that the cross-correlation between atopy and CBCL-INT was mainly due to genetic influences (77% of the covariance). This study supports the hypothesis that there is a shared genetic risk for atopy and internalizing symptoms.     

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)     

A comparison of digital luminescence mammography and conventional film - screen system: preliminary results of clinical evaluation

The heritability of total plasma testosterone levels, determined from blood samples, was examined in 160 adolescent twin pairs and their parents. Subjects were tested as part of a larger study of cardiovascular risk factors, conducted in Amsterdam. Each subject provided a sample of blood which was assayed to measure testosterone concentrations. Correlations of testosterone in monozygotic twins were higher than in dizygotic twins. No resemblance was found between testosterone values in fathers and those in their children and a moderate correlation was seen between mothers and their daughters. The lack of resemblance between family members of opposite sex suggests that different genetic factors influence plasma testosterone concentrations in men and women. In adolescent men, approximately 60% of the variance in testosterone levels is heritable. The lack of father-son resemblance suggests that different genetic factors may be expressed in adolescence and adulthood. In women, 40% of the variance in testosterone levels is heritable, both in adolescence and in adulthood.     

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

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

In search of shared and nonshared environmental factors in security of attachment: A behavior-genetic study of the association between sensitivity and attachment security.

The current article presents results from a twin study of genetic and environmental components of maternal sensitivity and infant attachment and their association. The sample consisted of 136 twin pairs from 2 sites: Leiden, the Netherlands, and London, UK. Maternal sensitivity was assessed in the home at 9-10 months, and infant attachment security was observed in the laboratory at 12 months. The study yielded little evidence that genetic factors are involved in variations between twins in maternal sensitivity ratings but did find that shared variance in maternal sensitivity was able to account for some of the similarity between twins in attachment security. Weak nonshared associations between sensitivity and attachment appeared to suppress the magnitude of the correlation between attachment and sensitivity in twin children. The results could indicate that the attachment security of one twin may depend on the relationship the parent has with the other twin. The results are brought to bear on the validity of attachment theory as a theory of primarily shared environmental effects in children's development and the continuing challenge posed to attachment theory by within-family differences in socioemotional processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inheritance of general intelligence.

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

epsilon-COP is a structural component of coatomer that functions to stabilize alpha-COP

A behavior genetic analysis of the personality dimension of ego development, as assessed by the Washington University Sentence Completion Test, was carried out on a sample of 45 pairs of monozygotic twins and 28 pairs of same-sex dizygotic twins. The twins ranged in age from 16 to 70 years at the time of assessment, had been separated during infancy, and had been raised apart in adoptive homes before being reunited in adulthood. Analyses indicated that reared-apart twins were similar in trait levels of ego development and that such similarity could not solely be attributed to measured similarity in cognitive ability, including verbal reasoning. Estimates of broad similarity for ego development (46%) were comparable to values reported for other major personality dimensions. Phenotypic variance in adult levels of ego development appears to have substantial genetic and environmental sources.     

Individual differences in adult ego development: Sources of influence in twins reared apart.

A behavior genetic analysis of the personality dimension of ego development, as assessed by the Washington University Sentence Completion Test, was carried out on a sample of 45 pairs of monozygotic twins and 28 pairs of same-sex dizygotic twins. The twins ranged in age from 16 to 70 years at the time of assessment, had been separated during infancy, and had been raised apart in adoptive homes before being reunited in adulthood. Analyses indicated that reared-apart twins were similar in trait levels of ego development and that such similarity could not solely be attributed to measured similarity in cognitive ability, including verbal reasoning. Estimates of broad heritability for ego development (46%) were comparable to values reported for other major personality dimensions. Phenotypic variance in adult levels of ego development appears to have substantial genetic and environmental sources. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual victimization in adolescent girls (age 15-20 years) enrolled in post-mandatory schools or professional training programmes in Switzerland

We investigated 21 pairs of twins for zygosity and idiopathic scoliosis. DNA fingerprinting confirmed that 13 pairs were monozygotic and eight were dizygotic. There was concordance for idiopathic scoliosis in 92.3% of monozygotic and 62.5% of dizygotic twins. Of the 12 pairs of monozygotic twins concordant for idiopathic scoliosis, six showed discordant curve patterns but eight had differences in Cobb angle of less than 10 degrees. Seven of the ten pairs of monozygotic twins had similar back shapes. Our findings suggest that there is a genetic factor in the aetiology of idiopathic scoliosis; they also indicate that there is a genetic factor in both the severity of the curve and the general shape of the back.     

Genetic correlations are not squared to determine common variance.

Comments on D. Ransom's (1973) criticism of C. Burt (1972) and A. R. Jensen (1972). Contrary to Ransom's assertion that the correlation coefficient obtained between IQ scores of monozygotic twins reared apart must be squared, the statistics of Burt and Jensen are appropriate for obtaining the percentage of IQ variance due to genetic factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A behavioral genetic study of trait emotional intelligence.

Numerous models of emotional intelligence (EI) have proposed the existence of hitherto undiscovered mental abilities, competencies, and skills. The theory of trait emotional intelligence suggests that the content domains of these models invariably contain permutations of personality traits. The two studies in this article examine the heritability of trait EI scores with a view to demonstrating empirically that the construct has a similar level of genetic influence as other personality traits. Study 1 was a family design of 133 high-school students and their parents. Regressions of offspring on midparent scores suggested median upper-limit heritability estimates of .18 at facet level, .25 at factor level, and .32 at the global trait EI level. Study 2 was a twin design (213 pairs of monozygotic [MZ] twins and 103 pairs of dizygotic [DZ] twins). It yielded median heritabilities of .42 for the facets, .44 for the factors, and .42 for global trait EI. Overall, our findings are in accordance with studies of the major personality dimensions and provide further empirical support for the conceptualization of EI as a personality trait. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modified intra-arterial calcium stimulation with venous sampling test for preoperative localization of insulinomas

BACKGROUND: Both genetic and environmental factors are thought to contribute to specific IgE responses, however, the relative contribution of each in the responses to individual ryegrass pollen allergens is largely unknown even though some responses to allergens have been linked to certain HLA complexes. OBJECTIVE: Using a large group of monozygotic and dizygotic twins, this study was designed to investigate the IgE binding profiles of individual ryegrass pollen (Lolium perenne) components to assess the relative contribution of genetic and environmental factors in determining IgE responses to specific allergens. METHODS: Ryegrass pollen proteins were separated by electrophoresis and immunoblotted with sera from 191 pairs of twins where at least one sibling had a SPT > 2 mm to perennial ryegrass. Concordance levels for individual ryegrass pollen components were compared between monozygotic and dizygotic twins in a subset group where both twins had SPT > 3 mm to perennial ryegrass. RESULTS: Immunoblotting revealed 23 individual IgE-binding components from ryegrass pollen. Although there was a significantly greater proportion of monozygotic twins with SPT wheals greater than 3 mm when compared with the dizygotic twins, the mean case-wise concordance for the immunoblot components was similar for both groups of twins. The mean case-wise concordance when at least four pairs of sera were involved was 44% for the MZ twins (n=11 components) and 45% for the DZ twins (n=12 components). We found no significant differences in concordance levels for any of the 23 individual components including allergens previously associated with HLA. CONCLUSION: Evidence for genetic control of allergen-specific IgE responses in a large population sample of twins to individual ryegrass allergens is limited, indicating that the IgE responses to specific ryegrass pollen allergens are determined largely by environmental factors.     

Nonshared environmental influences and personality differences in adult twins.

The twin design was used to examine the importance of different experiences of siblings within the family and to identify relations between twins' personality differences and their differential experiences. A sample of 161 monozygotic and 74 dizygotic twin individuals between the ages of 18 and 75 years retrospectively reported on their different experiences when growing up. The Sibling Inventory of Differential Experience (SIDE) was used for the first time with a sample of twin siblings. In addition, the twins provided self-report measures of affect and personality. In contrast to results from a sibling adoption design, this study of twins showed greater evidence for genetic variance in the SIDE scales. Nevertheless, the SIDE showed significant associations with differences in personality and affect for monozygotic twins, which reflect pure environment–behavior relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How to teach literature to medical students?

A pair of monozygotic twins suffering from noisy respirations and recurrent wheezes since early infancy were referred for evaluation. Using direct coronal CT and 3-dimensional reconstruction of the airway, congenital tracheobronchial stenosis was found in both twin babies, later confirmed by fibre optic bronchoscopy. The cause of congenital tracheobronchial stenosis remains obscure, but even in monozygotic twins an unidentified environmental factor cannot be excluded and may be responsible for discordant bronchopulmonary abnormalities. CONCLUSION: This case report shows that tracheobronchial stenosis may present in monozygotic twins. The pattern of malformation in twins differs from cases described previously.     

Determination of blood cystatin C in pregnant women during labor and in their newborns

BACKGROUND: Monozygotic (MZ) or "identical" twins arise from a single fertilized egg, which divides into two embryos at an early stage of development. As a result, MZ twins have identical genomes and are always of the same sex. METHODS: A case of optic nerve hypoplasia and anisometropia, in association with mirror-image presentation in a set of 12-year-old identical twins, is reported. The monozygotic twinning event responsible for identical twins--as well as the rare phenomenon of mirror imaging--is described. RESULTS: The combined occurrence of anisometropia and optic nerve hypoplasia in mirror-image presentation in a set of monozygotic twins provides a unique opportunity to study the genetic versus environmental influences on the development of optic nerve hypoplasia. CONCLUSIONS: Although the cause of optic nerve hypoplasia remains unclear, its associated mirror-image presentation in this case suggests a possible genetic predisposition.     

Comparison of methods for analyzing binary data arising from two-sample twin studies

The study of twins is widely used for research into genetic and environmental influences on human outcome measurements. For the study design in which independent samples of monozygotic and dizygotic twins are compared with respect to their similarity on a binary trait, several statistical methods have been proposed. Using a Monte Carlo simulation, we compare the five following procedures: 1) goodness-of-fit method based on the common correlation model, 2) normal approximation of the maximum likelihood estimators of the common correlation coefficients, 3) Ramakrishnan et al. [(1992) Genet Epidemiol 9:273-282] method of odds ratio comparison, 4) generalized estimating equations method of odds ratio estimation, and 5) tetrachoric correlation method. The results show that the goodness-of-fit approach has similar or better performance in both type-one error rates and power than the other methods in all parameter settings. Its advantage with respect to type-one error rates is particularly clear under conditions of small sample sizes, extreme prevalences, or high values of the intraclass correlation coefficients. Therefore, the goodness-of-fit method is recommended for the two-sample twin study design.