Identification of Twin Pairs From Large Population-Based Samples

Genetic and environmental contributions to perfectionism and its common factors

The aims of this study: (1) To evaluate the relative contributions of genetics and environment to perfectionism and it's two constructs: self-oriented, and socially prescribed perfectionism. (2) To clarify genetic and environmental common origins of both personal and social components.

METHODS

Participants were 258 pairs of adolescent Spanish twins. Socially prescribed and self-oriented perfectionism were assessed using the perfectionism subscale of the Eating Disorder Inventory.

STATISTICS

univariate and bivariate twin models, according to sex. Results; Heritability of self-oriented perfectionism was 23% in boys and 30% in girls, and of socially prescribed perfectionism 39% in boys and 42% in girls. Bivariate analysis suggested a common genetic and environmental pathway model. The genetic correlation between both perfectionisms was 0.981 in boys and 0.704 in girls. The non-shared environmental correlation was 0.254 in boys and 0.259 in girls. Conclusions; genetic influences on perfectionism are moderate during adolescence. Our results point toward a shared genetic component underlying both kind of perfectionism. These findings generate doubts about the hypothesis of a leading role of genetics in the pathogenesis of Self-oriented perfectionism and of environment in socially prescribed. The high genetic correlation seems to indicate that self-oriented and socially prescribed are the same dimension of perfectionism.

[Genetic and environmental contributions to body mass index in a Spanish adolescent twin sample]

BACKGROUND AND OBJECTIVE

Twin and family studies support large genetic influences on variability in body mass index (BMI), with heritability estimates ranging from 47% to over 90%. Our objective was to study the relative contributions of genetics and environment to BMI, evaluating sex differences, in an adolescent twin sample from Valencia, Spain.

MATERIAL AND METHODS

Five hundred eighty-four pairs of adolescent twins between 13 and 18 years of age completed the study (82 monozygotic [MZ] and 87 dizygotic [DZ] pairs of male twins, 118 MZ and 102 DZ pairs of female twins, and 195 opposite-sex pairs of DZ twins). To determine zygosity, teachers responded a questionnaire on physical similarity. They also measured the participant's height and weight. BMI was calculated and weight status was determined according to age. We used twin models to assess genetic and environmental (common and unique) factors affecting BMI.

RESULTS

There was a 7.1% frequency of overweight and 2.8% of obesity. The estimated heritability of BMI was 88.0% in boys and 72.1% in girls, with the remaining variance attributable to non-shared environment in boys (12.0%) and 8.8% in girls. It was only in girls that common environment had an effect on BMI.

CONCLUSIONS

Genetics appears to play an important role in explaining the variability in BMI in the adolescence, with slight variations between boys and girls. Common environmental factors exert their influence on BMI only in girls.

Genetic and environmental influences on psychological traits and eating attitudes in a sample of Spanish schoolchildren

INTRODUCTION

The heritability of eating disorders has been estimated to range from 22% to over 62%.The aim of this study is to determine the relative influence of genetics and environment that contribute to the drive for thinness, body dissatisfaction, perfectionism, and ineffectiveness, by evaluating sex differences in a sample of adolescent twins from Valencia, Spain.

MATERIAL AND METHODS

Five hundred eighty-four pairs of adolescent twins between 13 and 18 years of age completed the study. To determine zygosity, teachers responded to a questionnaire on physical similarity. Psychological traits of eating disorders were assessed with four sub-scales of the Eating Disorder Inventory (EDI); drive for thinness, body dissatisfaction, perfectionism, and ineffectiveness. Twin models were used to assess genetic and environmental (common and unique) factors affecting these four psychological traits.

RESULTS

All four traits showed significant genetic contributions among girls, with heritability estimates of 37.7% for ineffectiveness, 42.8% for perfectionism, 56.9% for drive for thinness, and 65.5% for body dissatisfaction. Among boys, body dissatisfaction showed no additive genetic contributions, indicating significant shared and individual specific environment effects. The three other traits in boys showed significant additive genetic contributions, but were lower than in girls.

CONCLUSIONS

With the exception of body dissatisfaction in boys, psychological traits of eating disorders show heritability patterns that differ according to sex.

The Project TALENT Twin and Sibling Study

Project TALENT is a US national longitudinal study of about 377,000 individuals born in 1942-1946, first assessed in 1960. Students in about 1,200 schools participated in a 2-day battery covering aptitudes, abilities, interests, and individual and family characteristics (Flanagan, 1962; www.projectTALENT.org). Follow-up assessments 1, 5, and 11 years later assessed educational and occupational outcomes. The sample includes approximately 92,000 siblings from 40,000 families, including 2,500 twin pairs and 1,200 other siblings of twins. Until recently, almost no behavior genetic research has been conducted with the sample. In the original data collection information was not collected with the intent to link family members. Recently, we developed algorithms using names, addresses, birthdates, and information about family structure to link siblings and identify twins. We are testing several methods to determine zygosity, including use of yearbook photographs. In this paper, we summarize the design and measures in Project TALENT, describe the Twin and Sibling sample, and present our twin-sib-classmate model. In most twin and family designs, the 'shared environment' includes factors specific to the family combined with between-family differences associated with macro-level variables such as socioeconomic status. The school-based sampling design used in Project TALENT provides a unique opportunity to partition the shared environment into variation shared by siblings, specific to twins, and associated with school- and community-level factors. The availability of many measured characteristics on the family, schools, and neighborhoods enhances the ability to study the impact of specific factors on behavioral variation.

Multivariate genetic analyses of cognition and academic achievement from two population samples of 174,000 and 166,000 school children

The genetic influence on the association between contemporaneously measured intelligence and academic achievement in childhood was examined in nationally representative cohorts from England and The Netherlands using a whole population indirect twin design, including singleton data. We identified 1,056 same-sex (SS) and 495 opposite-sex (OS) twin pairs among 174,098 British 11 year-olds with test scores from 2004, and, 785 SS and 327 OS twin pairs among 120,995 Dutch schoolchildren, aged 8, 10 or 12 years, with assessments from 1994 to 2002. The estimate of intelligence heritability was large in both cohorts, consistent with previous studies (h (2) = 0.70 ± 0.14, England; h (2) = 0.43 ± 0.28-0.67 ± 0.31, The Netherlands), as was the heritability of academic achievement variables (h (2) = 0.51 ± 0.16-0.81 ± 0.16, England; h (2) = 0.36 ± 0.27-0.74 ± 0.27, The Netherlands). Additive genetic covariance explained the large majority of the phenotypic correlations between intelligence and academic achievement scores in England, when standardised to a bivariate heritability (Biv h (2) = 0.76 ± 0.15-0.88 ± 0.16), and less consistent but often large proportions of the phenotypic correlations in The Netherlands (Biv h (2) = 0.33 ± 0.52-1.00 ± 0.43). In the British cohort both nonverbal and verbal reasoning showed very high additive genetic covariance with achievement scores (Biv h (2) = 0.94-0.98; Biv h (2) = 0.77-1.00 respectively). In The Netherlands, covariance estimates were consistent across age groups. The heritability of intelligence-academic achievement associations in two population cohorts of elementary schoolchildren, using a twin pair extraction method, is at the high end of estimates reported by studies of largely preselected twin samples.

Does Sharing the Same Class in School Improve Cognitive Abilities of Twins?

This article analyzes the effect of classroom separation of twins on their cognitive abilities, measured at different ages in Dutch primary education. We use a large longitudinal school-based sample of twins and their classmates. The analysis tries to reduce the bias by unobserved factors due to the nonrandom assignment of twins by taking into account differences in school environment, previous test scores and variation in class assignment between years. We find that classroom separation matters for language in Grade 2. Nonseparated twins score higher on language, and the difference is larger for same-sex pairs. This finding is robust for various methods that take unobserved effects into account. In addition, there is some evidence for higher scores in arithmetic in Grade 2. For the higher grades we find no effect of classroom separation on cognitive ability. In the analysis of the effect of a separation of at least 3 years we find that separation increases language performance between Grade 6 and 8 for opposite-sex pairs.

Incidence and risk factors of amniotic fluid embolisms: a population-based study on 3 million births in the United States

OBJECTIVE

Amniotic fluid embolism (AFE) is a condition occurring during delivery that can lead to severe maternal morbidity and mortality. Given the rarity of its occurrence, current estimates and predictors of the incidence and outcomes are often difficult to obtain.

STUDY DESIGN

We conducted a population-based cohort study on 3 million birth records in the Healthcare Cost and Utilization Project-Nationwide Inpatient Sample from 1999 to 2003 to estimate the incidence and case fatality of AFEs. Logistic regression was used to calculate the odds ratio (OR) and corresponding 95% confidence intervals (CIs) of demographic and obstetrical determinants of AFEs and fatal AFEs.

RESULTS

The overall incidence of AFE was 7.7 per 100,000 births (95% CI 6.7 to 8.7), with a case fatality rate of 21.6% (95% CI 15.5 to 27.6%). AFE was associated with maternal age greater than 35 (OR 2.2, 95% CI 1.5 to 2.1), placenta previa (OR 30.4, 95% CI 15.4 to 60.1), and cesarean delivery (OR 5.7, 95% CI 3.7 to 8.7). Although AFEs were not significantly associated with induction of labor (OR 1.5, 95% CI 0.9 to 2.3), they were associated with preeclampsia, abruptio placentae, and the use of forceps. Among women with an AFE, common demographic or obstetrical determinants were not predictive of maternal mortality.

CONCLUSION

AFE is a rare but serious condition that is associated with advanced maternal age, placental pathologies, and cesarean deliveries. Further research on the treatment of this condition is necessary.