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Maternal pre-pregnancy weight has been related with young singletons' cognitive and behavioral development, but it is not clear if it has an effect on temperament. We used a twin cohort to evaluate the association between maternal pre-pregnancy body mass index (BMI) and infants' temperament. The mothers of 834 twins answered questions regarding their pre-pregnancy BMI and their 0- to 18-month-old children's temperament using the Revised Infant Behavior Questionnaire. Three temperamental dimensions were examined: activity level, distress to limitation and duration of orienting. The relationship between maternal pre-pregnancy BMI and each temperamental component was investigated by means of multilevel mixed-effects linear regression analysis. We found no clear evidence of an association of maternal pre-pregnancy BMI with twins' temperament. The development of temperament is influenced by a large number of factors, probably different from those influencing children's emotional and behavioral development.

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

Dizygotic twinning rates have changed over time, which has been seen as a sign of a decline in fecundity. Since a woman's birthweight has been shown to be a marker of her fecundity, maternal birthweight may correlate with subsequent twinning rates. In the Danish National Birth Cohort (1996-2002), we examined if maternal birthweight, and whether she was born at term or preterm, correlated with her probability of multiple birth. For 20,719 live born infants, we had self-reported information about maternal birthweight, collected during the first wave of the 7-year follow-up, and information on multiple births from record linkage. The association between maternal birthweight and multiple births was investigated by use of logistic regression and presented as odds ratios (ORs) with 95% confidence intervals (CIs). Compared to women born at term with a birthweight of 3001-4000 g, women with a birthweight > 4500 g appeared to have higher chance of multiple birth while women with a birthweight of 4001-4500 had a lower chance, especially if the analysis was restricted to women with a BMI < 25 (Adjusted ORs 2.3 [1.0-5.4] and 0.4 [0.2-0.9] respectively). Odds ratios for dizygotic twinning were of the same magnitude. In women with a BMI >or= 25, no obvious pattern was present. Our findings do not indicate that twinning is a fecundity indicator. Women with a birthweight that may indicate a pregnancy complicated with gestational diabetes had the highest rate of multiple birth. These findings are new and should be put to a critical test in other data sources.

The aim of this study is to examine causes of individual differences in height, weight and body mass index (BMI) in 5-year-old children registered with the Netherlands Twin Register. In addition, we examine whether the results of twin studies can be expanded to the singleton population by comparing the data from twins to Dutch reference growth data and by looking at the twins' target height, which was derived from parental height. For 2996 5-year-old twin pairs, information on height and weight and on parental height was available. Univariate and bivariate genetic analyses of height and weight and univariate analyses of BMI were conducted. In order to compare the twins to the singleton population, standard deviation scores (SDS) for height, BMI and target height were calculated based on Dutch reference growth charts for the general population from 1997. Genetic influences were an important source of variation in height, weight and BMI and the main source of covariation between height and weight. Additive genetic factors accounted for 69% and 66% of the individual differences in height in boys and girls, respectively. For weight, heritability estimates were 59% in boys and 78% in girls and for BMI 34% and 74%. The influence of common environment on height was 25% and 27%, on weight 24% and 10% and on BMI 44% and 12% in boys and girls. The bivariate model showed a large overlap between the genes influencing height and weight. Genes explain 78% (in boys) and 76% (in girls) of the covariance between weight and height. At the age of 5 years, female twins were as tall as singleton children, while male twins were shorter than singletons. For both boys and girls, however, mean height SDS was 0.6 standard deviation scores below the mean target height. All twins had lower BMI than singletons. Twins grow fairly well compared to singletons, but they grow below their target height. This may be due to the above average height of twin parents.

The aim of this study was to evaluate the differences in the metabolic profile and body composition of monozygotic (MZ) twins concordant and discordant for the practice of physical exercise. The sample consisted of 92 MZ twins (72.5% female and 27.5% male, mean age 25.4 ± 5.69 years), registered with the Brazilian Registry of Twins, residing in Natal, Brazil. Data collection was carried out between the years 2016 and 2018. On day 1, subjects underwent a whole-body fitness evaluation, including measures of weight, height, body composition by Dual-Energy X-ray Absorptiometry and the Cardiorespiratory Exercise Test. On day 2, 10 ml blood samples were collected (overnight fasting) to determine the lipid profile and fasting glucose. The sample was separated into three groups: Active Concordant twins (Concordant A, n = 44 subjects), Inactive Concordant twins (Concordant I, n = 22 subjects) and Discordant pairs for Physical Exercise (Discordant PE, n = 26 subjects). The results demonstrated a difference between the discordant twins for exercise and also between the active versus sedentary groups, indicating a causal effect of exercise on the fat percentage, maximum oxygen consumption (VO2max) and second ventilatory threshold variables. Between groups, a difference was also observed between the groups in ventilatory threshold, very low-density lipoprotein and triglycerides. We concluded that, regardless of genetics, the practice of physical exercise was sufficient to generate alterations in body composition and VO2max in MZ twins, but not in the lipid profile or fasting glucose. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the effects of intrauterine environment on the magnitude of intrapair differences in six somatic traits of monozygotic (MZ) and dizygotic (DZ) twins (1,263 pairs; 424 MZ twins and 839 DZ twins). Differences in intrauterine environments of MZ twins enforced division of the research material into four groups: (1) MZ-MC-TTTS — MZ twins from monochorionic (MC) pregnancies with twin-to-twin transfusion syndrome (TTTS), (2) MZ-MC (without TTTS)—MZ twins from MC pregnancies without TTTS, (3) MZ-DC—MZ twins from dichorionic (DC) pregnancies, and (4) DZ—DZ twins. The intrapair differences in all analyzed somatic traits, especially body weight and circumference of the chest, were the largest in the case of MZ twins from MC pregnancies with TTTS. DZ twins were the group presenting with the second largest intrapair differences in the analyzed traits. At the end of pregnancy, that is, in lunar months 9 and 10, the magnitude of intrapair differences in all traits of twins from this group was significantly greater than in MZ twins from both MC and DC pregnancies. Irrespective of the analyzed period, the least evident, statistically insignificant intrapair differences in the studied traits were documented in the case of MZ twins from MC pregnancies without TTTS and twins from DC pregnancies. These findings imply that the differentiating effect of intrauterine environment is associated with the occurrence of TTTS, rather than with chorionicity, as postulated previously. [ABSTRACT FROM AUTHOR]

This study examined the genetic and environmental effects on variances in weight, height, and body mass index (BMI) under 18 years in a population-based sample from China. We selected 6,644 monozygotic and 5,969 dizygotic twin pairs from the Chinese National Twin Registry (CNTR) aged under 18 years (n = 12,613). Classic twin analyses with sex limitation were used to estimate the genetic and environmental components of weight, height, and BMI in six age groups. Sex-limitation of genetic and shared environmental effects was observed, especially when puberty begins. Heritability for weight, height, and BMI was low at 0–2 years old (less than 20% for both sexes) but increased over time, accounting for half or more of the variance in the 15–17 year age group for boys. For girls, heritabilities for weight, height and BMI was maintained at approximately 30% after puberty. Common environmental effects on all body measures were high for girls (59–87%) and presented a small peak during puberty. Genetics appear to play an increasingly important role in explaining the variation in weight, height, and BMI from early childhood to late adolescence, particularly in boys. Common environmental factors exert their strongest and most independent influence specifically in the pre-adolescent period and more significantly in girls. These findings emphasize the need to target family and social environmental interventions in early childhood years, especially for females. Further studies about puberty-related genes and social environment are needed to clarify the mechanism of sex differences. [ABSTRACT FROM PUBLISHER]

Systolic and diastolic blood pressure, pulse pressure (PP), and body mass index (BMI) are heritable traits in human metabolic health but their common genetic and environmental backgrounds are not well investigated. The aim of this article was to explore the phenotypic and genetic associations among PP, systolic blood pressure (SBP), diastolic blood pressure (DBP), and BMI. The studied sample contained 615 twin pairs (17–84 years) collected in the Qingdao municipality. Univariate and multivariate structural equation models were fitted for assessing the genetic and environmental contributions. The AE model combining additive genetic (A) and unique environmental (E) factors produced the best fit for each four phenotypes. Heritability estimated in univariate analysis ranged from 0.42 to 0.74 with the highest for BMI (95% CI 0.70–0.78), and the lowest for PP (95% CI 0.34–0.49). The multivariate model estimated (1) high genetic correlations for DBP with SBP (0.87), PP with SBP (0.75); (2) low–moderate genetic correlations between PP and DBP (0.32), each BP component and BMI (0.24–0.37); (3) moderate unique environmental correlation for PP with SBP (0.68) and SBP with DBP (0.63); (4) there was no significant unique environmental correlation between PP and BMI. Overall, our multivariate analyses revealed common genetic and environmental backgrounds for PP, BP, and BMI in Chinese twins. [ABSTRACT FROM PUBLISHER]

We aimed to investigate the association between weight change from 20 years of age and insulin resistance (IR), and genetic and environmental relationships between these traits. In 594 Korean twins and family members (209 men, 385 women, 44.0 ± 10.8 years old), the percentage of weight change was calculated using self-reported body weight at 20 years of age and currently measured bodyweight. IR traits were assessed using fasting plasma glucose and insulin, the homeostasis model assessment of IR index (HOMA-IR), and the quantitative insulin sensitivity check index (QUICKI). Linear mixed analysis was applied after adjusting for household, body mass index (BMI) at the age of 20 years, age, sex, alcohol, smoking, physical activity, and caloric intake. Heritabilities and genetic and environmental correlations were estimated after adjusting for covariates. In 55 monozygotic twin pairs discordant for HOMA-IR level by >0.3, a conditional logistic regression analysis was conducted regarding weight change. Increases in glucose, insulin, and HOMA-IR and a decrease in QUICKI were associated with a higher percentage of weight change (p < .05). Estimated heritabilities for IR traits were 0.401–0.606 (p < .001). In cross-trait relationships, environmental correlations were -0.43–0.42 (p < .05 for all IR), while genetic correlations were -0.27–0.27 (p < .05 for QUICKI, insulin, and HOMA-IR). In 55 pairs of monozygotic twins, the odds ratio (95% confidence interval) for having a higher level of HOMA-IR was 1.10 (1.03–1.17) with 1% increase in weight change since 20 years old, after adjusting for lifestyle-related factors. In conclusion, both genetic and environmental influences played significant roles in the positive association between weight change from 20 years of age and IR. [ABSTRACT FROM PUBLISHER]

BackgroundThree cognitive constructs are risk factors for eating disorders: undue influence of weight and shape, concern about weight and shape, and body dissatisfaction (BD). Undue influence, a diagnostic criterion for eating disorders, is postulated to be closely associated with self-esteem whereas BD is postulated to be closely associated with body mass index (BMI). We understand less about the relationships with concern about weight and shape. The aim of the current investigation was examine the degree of overlap across these five phenotypes in terms of latent genetic and environmental risk factors in order to draw some conclusions about the similarities and differences across the three cognitive variables.MethodA sample of female Australian twins (n=1056, including 348 complete pairs), mean age 35 years (s.d.=2.11, range 28–40), completed a semi-structured interview about eating pathology and self-report questionnaires. An independent pathways model was used to investigate the overlap of genetic and environmental risk factors for the five phenotypes.ResultsIn terms of variance that was not shared with other phenotypes, self-esteem emerged as being separate, with 100% of its variance unshared with the other phenotypes, followed by undue influence (51%) and then concern (34%), BD (28%) and BMI (32%).ConclusionsIn terms of shared genetic risk, undue influence and concern were more closely related than BD, whereas BMI and BD were found to share common sources of risk. With respect to environmental risk factors, concern, BMI and BD were more closely related to each other than to undue influence. [ABSTRACT FROM PUBLISHER]

Objective: To evaluate the influence of gestational diabetes mellitus on weight discrepancy in twin pregnancies.Methods: 200 twin pregnancies were included in the study. 157 nondiabetic pregnant women with twin gestations and 43 twin pregnancies with gestational diabetes mellitus (GDM) with viable fetuses born after 24 weeks of gestation were enrolled. Influence of maternal age, body-mass-index at the time of the oral glucose tolerance test, parity, smoking, chorionicity, gestational age at delivery and diagnosis of GDM on weight discrepancy of the twins was evaluated.Results: Mean weight discrepancy of all analyzed twin pregnancies was 285 grams (+/- 231), relative weight discrepancy was 11.3% (+/- 8.6). Univariate regression analyses showed that GDM, chorionicity and gestational age at delivery were significantly associated with weight discrepancy. In the multivariate model only diagnosis of GDM was significantly associated with weight discrepancy.Conclusion: Twin pregnancies with insulin requiring gestational diabetes seem to have less birth weight discrepancy than twin pregnancies with normal glucose tolerance. [ABSTRACT FROM AUTHOR]

Gemini is a cohort study of young twins in the United Kingdom designed to assess genetic and environmental influences on early childhood weight trajectories with a focus on infant appetite and the family environment. A total of 2402 families with twins born in England and Wales between March and December 2007 agreed to participate and returned completed baseline questionnaires. The sample includes 1586 same-sex and 816 opposite-sex twins. The study is currently funded for 5 years of follow-up, but is planned to continue into early adolescence and beyond, pending funding. With current funding of the study, families will be followed up when twins are: 8 months old (baseline), and then at 15, 20, 24, 36 and 48 months of age. Gemini is in its early stages, with baseline and first follow-up data collection completed. This is the first twin cohort to focus on childhood weight gain with detailed and repeated measures of children's appetite, food preferences, activity behavior and parental feeding styles, alongside detailed and repeated collection of anthropometrics. This article reviews the rationale for the Gemini study, its representativeness and the main measures. [ABSTRACT FROM AUTHOR]

The present study examined the effects of chorionicity of twins on variations of height, weight, and body mass index (BMI) during childhood in the classical twin design. Mothers of 81 pairs of monochorionic monozygotic (MCMZ), 47 pairs of dichorionic monozygotic (DCMZ), and 457 pairs of dizygotic (DZ) twins drawn from the South Korean Twin Registry reported their children's height and weight. Twins' age ranged from 1.9 to 8.7 yrs, with a mean of 4.0 yrs and SD of 1.7 yrs. We computed maximum likelihood twin correlations and performed model-fitting analyses. In correlational and model-fitting analyses, we treated age and sex as covariates to control their main effects. Maximum likelihood MCMZ, DCMZ, and DZ twin correlations were, respectively, .96, .92, and .74, for height, .88, .91, and .57 for weight, and .93, .92, and .61 for BMI. The pattern of these twin correlations suggested very modest chorion effects on body measures. Model-fitting analyses confirmed the observations from twin correlations. Whereas genetic and shared environmental influences were significant for all three body measures, chorion effects attained statistical significance only for height (4%), and those for weight and BMI were zero. These findings indicate that genetic and environmental estimates for height, weight, and BMI during childhood are biased little by the chorion type of MZ twins, supporting the validity of the equal prenatal environment assumption in the classical twin design. [ABSTRACT FROM AUTHOR]

A high body mass index (BMI) is commonly used as an index of overweight and obesity. There is persistent evidence of high heritability for variation in BMI, but the effects of common environment appear inconsistent across different European countries. Our objective was to compare genetic and environmental effects on BMI in a sample of twins from two different European countries with distinct population and cultural backgrounds. We analysed data of adult female twins from the Netherlands Twin Register (222 monozygotic [MZ] and 103 dizygotic [DZ] pairs) and the Murcia Twin Register (Spain; 202 MZ and 235 DZ pairs). BMI was based on self-reported weight and height. Dutch women were taller and heavier, but Spanish women had a significantly higher mean BMI. The age related weight increase was significantly stronger in the Spanish sample. Genetic analyses showed that genetic factors are the main contributors to variation in height, weight, and BMI, within both countries. For height and weight, estimates of genetic variances did not differ, but for height, the estimate for the environmental variance was significantly larger in Spanish women. For BMI, both the genetic and the environmental variance components were larger in Spanish than in Dutch women. [ABSTRACT FROM AUTHOR]

We examined the contributions of genetic and environmental factors to body mass index (BMI) over approximately 28 years. Participants were 693 male, predominantly middle-class, twins (355 monozygotic, 338 dizygotic) from the Vietnam Era Twin Registry. The phenotypic correlation between age 20 and age 48 BMI was 0.52; the genetic correlation was 0.60. Most of the remaining variance at both times was accounted for by nonshared environmental factors. Since genetic factors are not perfectly correlated, this indicates that other genes affect BMI at one or both time points, leaving room for further exploration of the genetics of body mass stability. Mean BMI increased significantly from 22.7 (normal) to 27.8 (overweight). Overweight BMI at age 20 predicted midlife adult onset diabetes (adjusted odds ratio = 4.62, 95% CI 1.91 to 11.18), but not hypertension. Depending on one's vantage point, the results indicate elements of both stability and change in BMI. Very similar phenotypic and genetic correlations were observed over a similar time period in a WW II twin sample, but without the substantial mean increase in BMI. It seems unlikely that different genes influence BMI in the two cohorts. Therefore, we argue that nonshared environmental factors are probably primarily responsible for the secular increase in midlife BMI. Our results also provide prospective evidence that early excess BMI may have serious long-term health consequences, and that this risk is not limited to minorities or adults of lower socioeconomic status. [ABSTRACT FROM AUTHOR]

Genetic and environmental contributions to body size from birth to 5 years in a population-based twin cohort were studied. Sex differences in gene-environment etiology were also explored. Analyses used data from the Quebec Newborn Twin Study (QNTS), a population-based birth cohort of 672 twin pairs. The final sample consisted of 177 complete twin pairs. Heritability of weight was moderate at birth while common environmental factors accounted for almost half of the variance. Influence of family environment disappeared by 5 months and genetic effects were high (approximately 90%) for both sexes at 5 months and 5 years. Adjustment of weight for height yielded similar results as for weight alone. Slight but significant sex-limitation of genetic effects was observed at 5 months. Overall, genetic factors accounted for 40% of birthweight variance, with intrauterine environment influences explaining almost half. However, genetic factors accounted for most of the variance in weight. These results do not imply a lack of environmental effects on body weight, but rather a lack of: (1) environmental effects that are independent from genetic liability, and/or (2) a lack of significant environmental variation in the population (e.g., uniform nutritional habits) that leaves genetic differences between children to generate most of the variance in weight. [ABSTRACT FROM AUTHOR]

Background. Theory and evidence strongly suggest that perfectionism may be a risk factor for eating disorders. The purpose of the current study was to investigate a model that would explain the relationship between the cognitive diagnostic criterion for both anorexia nervosa and bulimia nervosa, namely undue influence of body weight or shape on self-evaluation, and dimensions of perfectionism. The model of particular interest was the common cause model, which hypothesizes that the phenotypes are caused by the same underlying genetic and environmental risk factors.Method. Female twins (n=1002) from the Australian Twin Registry (ATR), aged 28 to 39 years, were interviewed using the Eating Disorder Examination (EDE). In addition, questions relating to the Equal Environment Assumption (EEA) and the Frost Multidimensional Perfectionism Scale, namely concern over mistakes (CM), personal standards (PS) and doubts about actions (DA), were assessed.Results. There was no evidence of violation of the EEA for any of the four phenotypes. Univariate models showed all phenotypes to be influenced by both genetic and non-shared environmental action, where genetic estimates ranged from 25% to 39% of the variance. Multivariate analyses suggested the best explanation of covariation among the phenotypes was an independent pathways, rather than a common pathways, model.Conclusions. Undue influence of body weight or shape on self-evaluation shared about 10% of its sources of genetic and environmental variance with perfectionism, thus suggesting that a common cause model does not represent the best explanation of the relationship between perfectionism and this cognitive diagnostic criterion for eating disorders. [ABSTRACT FROM AUTHOR]

Human growth is a complex and poorly understood process. We studied the effect of genetic and environmental factors on height and body mass index (BMI, kg/m(2)) based on maternal reports at 3, 4, 5, 7, 10 and 12 years of age in a large longitudinal cohort of Dutch twins (7755 complete twin pairs at age 3). Several multivariate variance component models for twins were fitted to the data using the Mx statistical package. The first-born twin was taller until age 10 and heavier until age 12 than the second-born co-twin. Heritability estimates were high for height (a(2) = .58-.91) and BMI (a(2) = .31-.82), but common and unshared environmental factors were also important. The phenotypic correlations across the ages for height and BMI were mainly explained by correlated additive genetic factors (r(a) = .77-.96 for height and .43-.92 for BMI), but common (r(c) = .40-.84 and .09-.78, respectively) and specific environmental correlations (r(e) = .50-.81 and .42-.80, respectively) were also significant. Additive genetic factors decreased with increasing age difference for both height and BMI. However, the full Cholesky model, which does not make any assumptions regarding the underlying genetic structure, had the best fit. High genetic correlations across the ages, especially for height, may help further molecular genetic studies of human growth. Environmental factors affecting height and BMI during growth period are also important, and further studies are needed to identify these factors and test whether they interact with genetic factors. [ABSTRACT FROM AUTHOR]