Comparative study of the consumption of cariogenic food in monozygotic and same-sex dizygotic twins

The eating habits of the 111 monozygotic and 67 like-sexed dizygotic twins were compared with respect to cariogenic foods. The food habits were recorded using a seven-day dietary history with the weekly frequency of the cariogenic foods examined. The biometrical analysis showed that the eating habits of the monozygotic pairs were more similar than that of the dizygotic twin pairs. The differences were statistically significant. Based on these findings, it seems that genetic factors play a role in the development of the food habits.     

Heritability of body size and muscle strength in young adulthood: a study of one million Swedish men

Moderate heritability for skeletal muscle strength has been reported in twin studies, but genetic co-variation between muscle strength at different parts of body and body size is not well known. Further, representativeness of twin cohorts needs to be critically evaluated. Height, weight, elbow flexion, hand grip and knee extension strength were measured in young adulthood in 1,139,963 Swedish men born between 1951 and 1976. We identified 154,970 full-brother pairs and 1582 monozygotic (MZ) and 1864 same-sex dizygotic (DZ) complete twin pairs. The data were analyzed using quantitative genetic modeling for twin and family data. Twins compared to singletons and MZ twins compared to DZ twins were shorter, lighter and had lower muscle strength. In singletons, there was more variation in weight and the strength measures compared to twins with known zygosity but not when compared to twins with unknown zygosity. Full-sib correlations for these traits were lower than DZ correlations. Additive genetic factors explained 81% of variation in height, 59% in body mass index and 50-60% in the strength measures. Additive genetic correlations varied from 0.13 between height and elbow flexion strength to 0.78 between elbow flexion and hand grip strength. Our results suggest that extra variation may exist in general populations not found in twin samples, probably because of selection due to non-participation. This may have inflated heritability estimates in previous twin studies. Nonetheless, we showed that genetic factors affect muscle strength and part of these genes are common to different strength indicators and body size.     

Contribution of genetic and environmental influences to ankle-brachial blood pressure index in the NHLBI Twin Study. National Heart, Lung, and Blood Institute

The ankle-brachial index (ABI) is widely used in the clinical diagnosis of peripheral arterial disease. The contributions of genetic and environmental influences to normal and abnormal ABI values are unknown. In this study, the authors used available data on 94 monozygotic pairs and 90 dizygotic pairs of elderly, White, male twins examined in 1995-1997 to investigate the contributions of genetic and environmental influences to normative ABI values. Within-twin-pair correlations for normative ABI values were statistically significant, and the correlation in monozygotic twin pairs was significantly greater than that in dizygotic pairs. Structural equation modeling of the variance-covariance matrices of monozygotic and dizygotic twins indicated that 48% of the observed variability in ABI values could be attributed to additive genetic effects. In contrast, concordance rates for low ABI values (ABI< or =0.9) for both monozygotic and dizygotic twins were significantly greater than would be expected by chance alone, but within-pair monozygotic similarity was not significantly greater than dizygotic similarity. A matched-cotwin analysis in 21 pairs that were discordant for low ABI values found that twins with low ABI values were physically less active and more likely to be persistent smokers than their normal-control brothers. These findings reinforce the role of individual health practices (e.g., physical activity, smoking) in the manifestation of peripheral arterial disease among subjects matched for age, genetics, and early shared environment.     

成年双生子血尿酸遗传度研究

目的 用双生子研究方法 对成年人血尿酸的遗传度进行估计.方法 从青岛双生子库募集成年双生子.测量身高、体重和血尿酸.相同性别的双生子采用16个多态标记进行卵型鉴定.通过校正年龄、性别和BMI,来构建结构方程模型估计遗传度.结果 共收集687对双生子数据,其中同卵双生子420对,异卵双生子267对.经平方根转换后,男性血尿酸水平(17.47±1.91)略高于女性(15.22±1.70)(P＜0.0001),通过校正年龄、性别和BMI后双生子血尿酸的组内相关系数分别为,同卵双生子0.70、异卵双生子0.40.运用性别限制模型进行拟合,最佳模型AE模型,加性别遗传因素和特殊环境因素共同作用血尿酸的水平.血尿酸的遗传度为70.5%(95%CI:65.9～74.6),特殊环境因素占29.5%(95%CI:25.4～34.2).结论 遗传因素是影响样本双生子血尿酸水平的主要因素.     

Birth weight and risk of angina pectoris: analysis in Swedish twins

Objective: Intrauterine nutrition approximated by birth weight has been shown to be inversely associated with risk of coronary heart disease (CHD). By investigating the association within twin pairs discordant for disease, the influence of genetic and early environmental factors is substantially reduced. Methods: We have investigated the association between birth weight and angina pectoris in same-sexed twins with known zygosity included in the population-based Swedish Twin Registry. Self-reports of birth weight and angina pectoris were collected in a telephone interview between 1998 and 2000. The cohort analyses were based on 4594 same-sexed twins, and the within-pair analyses included 55 dizygotic and 37 monozygotic twin pairs discordant for angina pectoris. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by logistic regression. Results: Compared with birth weight between 2.0 and 2.9 kg, low birth weight (<2.0 kg) was associated with increased risk of angina pectoris in the twin cohort, (OR: 1.46; 95% CI: 1.14–1.87), but after adjustment for potential confounders the risk decreased, and did not reach significance. Within twin pairs discordant for angina pectoris, low birth weight was significantly associated with increased risk of angina pectoris within dizygotic twins (adjusted OR: 5.73; 95% CI: 1.59–20.67), but not within monozygotic twins (adjusted OR: 1.20; 95% CI: 0.40–3.58). Conclusions: The results suggest that genetic differences associated with foetal growth and adult risk of CHD may have affected previously reported associations between birth weight and CHD.     

Genetic susceptibility to burnout in a Swedish twin cohort

Most previous studies of burnout have focused on work environmental stressors, while familial factors so far mainly have been overlooked. The aim of the study was to estimate the relative importance of genetic influences on burnout (measured with Pines Burnout Measure) in a sample of monozygotic (MZ) and dizygotic (DZ) Swedish twins. The study sample consisted of 20,286 individuals, born 1959–1986 from the Swedish twin registry who participated in the cross-sectional study of twin adults: genes and environment. Probandwise concordance rates (the risk for one twin to be affected given that his/her twin partner is affected by burnout) and within pair correlations were calculated for MZ and DZ same—and opposite sexed twin pairs. Heritability coefficients i.e. the proportion of the total variance attributable to genetic factors were calculated using standard biometrical model fitting procedures. The results showed that genetic factors explained 33% of the individual differences in burnout symptoms in women and men. Environmental factors explained a substantial part of the variation as well and are thus important to address in rehabilitation and prevention efforts to combat burnout.     

Characteristics associated with excessive weight gain after smoking cessation in men.

OBJECTIVES. Data from two surveys of the National Academy of Sciences-National Research Council Twin Registry, conducted 16 years apart, were used to determine characteristics of individuals that were predictive of excessive weight gain after smoking cessation. METHODS. Over the follow-up, 2179 men quit smoking and averaged a weight gain of 3.5 kg. Quitters were grouped into four categories of weight change: lost weight, no change, gained weight, and excessive weight gain ("super-gainers"). RESULTS. In comparison with quitters reporting no change in weight, super-gainers were younger, were of lower socioeconomic status, and differed on a number of health habits before quitting (all Ps < .05). At follow-up, super-gainers reported changes in health habits that were significantly different from those seen in quitters reporting stable weight (all Ps < .05). Pairwise concordance for weight change in 146 monozygotic and 111 dizygotic twin pairs in which both twins quit smoking was significantly greater in monozygotic than dizygotic pairs (P < .01). CONCLUSIONS. These results indicate that super-gainers differ in important ways from those who do not gain weight after smoking cessation and that these weight changes may be influenced by underlying genetic factors.     

Genetic and environmental influences on the tracking of body size from birth to early adulthood

OBJECTIVE: This study identified genetic and environmental influences on the tracking of body size from birth to 16 to 18.5 years of age. RESEARCH METHODS AND PROCEDURES: Longitudinal information was collected from a nationally representative sample of Finnish twin adolescents (birth cohorts 1975 to 1979) and their parents through questionnaires mailed when the twins were ages 16 and 18.5 years old. The sample included 702 monozygotic, 724 same-sex dizygotic, and 762 opposite-sex dizygotic sets of twins. The measures used were length, weight, ponderal index (kilograms per cubic meters), and gestational age at birth, and height, weight, and body mass index (kilograms per square meters) at 16 to 18.5 years of age. The changes in genetic and environmental influences on body size from birth to early adulthood were analyzed by quantitative genetic modeling. RESULTS: The twins who had a higher weight or ponderal index at birth were taller and heavier in early adulthood, whereas those who were longer at birth were taller, but not heavier, later in life. Adult height was affected more by the birth size than body mass index. In the genetic modeling analyses, the genetic factors accounting for the variation of body size became more apparent with age, and both genetic and environmental influences on stature had a sizable carry-over effect from birth to late adolescence, whereas for relative weight, the influences were more age-specific. DISCUSSION: The genetic and environmental architecture of body size changes from birth to adulthood. Even in monozygotic twins who share their genetic background, the initially larger twin tended to remain larger, demonstrating the long-lasting effects of fetal environment on final body size.     

OBESITY: NATURE OR NURTURE?

This study of monozygotic and dizygotic Swedish twins raised together and apart focuses attention on the genetic contribution to body habitus. Although genetics clearly plays a role in the genesis of obesity, this study relied on body mass index and provides more support for the inheritance of frame size or fat-free mass than for the inheritance of obesity.     

Parental feeding style and the inter-generational transmission of obesity risk

OBJECTIVE: This study was designed to determine whether a community sample of obese mothers with young children used different feeding styles compared with a matched sample of normal-weight mothers. Four aspects of feeding style were assessed: emotional feeding, instrumental feeding (using food as a reward), prompting/encouragement to eat, and control over eating. RESEARCH METHODS AND PROCEDURES: Participants were from 214 families with same-sex twins; 100 families in which both parents were overweight or obese and 114 in which both parents were normal weight or lean. RESULTS: We found that obese mothers were no more likely than normal-weight mothers to offer food to deal with emotional distress, use food as a form of reward, or encourage the child to eat more than was wanted. The obese and normal-weight mothers did differ on "control"; obese mothers reported significantly less control over their children's intake, and this was seen for both first-born and second-born twins. Twin analyses showed that these differences were not in response to children's genetic propensities, because monozygotic correlations were no greater than dizygotic correlations for maternal feeding style. DISCUSSION: These results suggest that the stereotype of the obese mother, who uses food in nonnutritive ways so that her child also becomes obese, is more likely to be myth than fact. However, the results raise the possibility that lack of control of food intake might contribute to the emergence of differences in weight.     

Low birthweight and Type 2 diabetes: a study on 11 162 Swedish twins

BACKGROUND: To investigate the association between low birthweight and diabetes in a population-based Swedish twin sample. Method A cohort of 11 162 same-sexed Swedish twins born between 1906 and 1958 was used in order to investigate the risk of developing Type 2 diabetes between and within twin pairs by utilizing random effects linear models. RESULTS: Between pairs there was a significant increase in risk of developing Type 2 diabetes for a 1-kg increase in their mean birthweight (odds ratio [OR] = 2.13; P < 0.01), adjusted for age, sex, body mass index (BMI), and smoking status. The corresponding risk within pair was 2.03 (P = 0.07) for monozygotic twins and 1.15 (P = 0.71) for dizygotic twins. The test of the heterogeneity of the within and between effects showed no significant difference between the estimates. CONCLUSIONS: The study suggests that reduced fetal growth increase the risk of Type 2 diabetes due to an in utero programming effect possibly caused by intrauterine malnutrition. However, it does not exclude the possibility of a common genetic mechanism.     

Weight change in monozygotic twins treated with valproate

OBJECTIVE: To evaluate whether genetic factors contribute to weight gain associated with valproate (VPA) therapy. RESEARCH METHODS AND PROCEDURES: We retrospectively and prospectively evaluated five pairs of monozygotic twins concordant for epilepsy and treated with VPA regarding weight course. RESULTS: In all twin pairs, both twins showed similar weight courses under therapy with VPA. DISCUSSION: These results suggest that genetic factors may have an influence on the weight change induced by VPA. Further studies are necessary to obtain heritability estimates regarding this effect of VPA therapy and to identify the relevant genes.     

The role of genetic and environmental factors in the association between birthweight and blood pressure: evidence from meta-analysis of twin studies

BACKGROUND: An inverse association between birthweight and later blood pressure has been found in many studies in singletons. Twin studies have been used to examine whether genetic factors or family environment could account for this association. METHODS: A systematic review identified 10 studies covering 3901 twin pairs. Meta-analysis of regression coefficients for the association between birthweight and systolic blood pressure was carried out for unpaired versus paired associations and for paired associations in dizygotic versus monozygotic pairs. RESULTS: After adjustment for current weight or body mass index (BMI), the difference in systolic blood pressure per kg birthweight was -2.0 (95% CI: -3.2, -0.8) mmHg in the unpaired analysis and -0.4 (95% CI: -1.5, 0.7) mmHg in the paired analysis in the same subjects. In the paired analysis by zygosity, in all twins the coefficients were -0.7 (95% CI: -2.3, 0.8) mmHg in dizygotic pairs and -0.8 (95% CI: -2.1, 0.4) mmHg in monozygotic pairs, but in studies which included zygosity tests the coefficients were -1.0 (95% CI: -3.3, 1.6) mmHg in dizygotic pairs and -0.4 (95% CI: -1.9, 1.3) mmHg in monozygotic pairs. CONCLUSIONS: The attenuation of the regression coefficient in the paired analysis provides support for the possibility that factors shared by twins contribute to the association between birthweight and blood pressure in singletons. Comparison of paired analysis in monozygotic and dizygotic pairs could not provide conclusive evidence for a role for genetic as opposed to shared environmental factors.     

Bulimia nervosa in eleven sets of twins: A clinical report

Eleven sets of twins (6 monozygotic and 5 dizygotic, including one pair who was adopted away and another who was brought up in a separate foster home) in which the proband had bulimia nervosa were described. The concordance rate among the monozygotic twins was 33% and among the dizygotic twins was 0%. The possible genetic predisposition mechanisms were discussed.     

Lifestyle factors in monozygotic and dizygotic twins

In examining genetic influences on biological variables using twins, it may be important to examine the distribution between and within twin pairs of demographic and lifestyle factors that may themselves affect the biological variable being studied. We explored the distribution of demographic and lifestyle factors that may affect blood lipid levels or ischaemic heart disease (IHD) risk among a sample of 106 monozygotic (MZ) and 94 like-sex dizygotic (DZ) twin pairs. In our sample, MZ twins were statistically significantly different from DZ twins only in marital status, cigarette smoking habits, and the ratio of polyunsaturated to saturated fat (P:S ratio) in their dietary intake. The latter variable was among many dietary variables examined (using 4-day weighed food diaries), and the size of the difference in intake was small. When comparisons were made of the similarities within twin pairs, we found members of MZ twin pairs to be statistically significantly closer than DZ twins in educational achievement, occupation, cigarette smoking, and exercise habits, and the number of days a week on which alcohol was consumed. These last three variables were consistently closer among twins with closer contact than among those with a smaller degree of current shared environment. For 12 of the 13 nutrients examined, the within-pair correlations were higher for MZ than for DZ twins, although our test for significant genetic variance showed statistical significance only for intake of complex carbohydrates. We conclude that MZ twins share demographic and lifestyle factors that might influence the risk of IHD and blood lipid levels to a greater degree than do DZ twins, although it is difficult to say if these similarities in lifestyle result from genetic influences or not. Nevertheless, ascribing differences between correlations in MZ and DZ twin pairs for lipid levels as being purely "genetic"--as implicit in conventional measures of heritability--is likely to overestimate the influence of genetic factors.     

The correlation of fecundability among twins: evidence of a genetic effect on fertility?

BACKGROUND: Numerous rare genetic conditions are known to influence fecundability in both males and females. It is less clear to what extent more subtle genetic differences influence fecundability on a population level. METHODS: In 1994 a population-based survey was conducted among Danish twins born 1953-1982. Fecundability was assessed as the waiting time to pregnancy at the first attempt to achieve a pregnancy. RESULTS: The reported time to pregnancy for males was slightly shorter than for females but there were no sex differences in intrapair similarity. We found an intrapair correlation in time to pregnancy for 645 monozygotic twin pairs (r = 0.22; 95% confidence interval = 0.12 to 0.32), but no intrapair correlation for 826 like-sex dizygotic twin pairs (r = 0.00; 95% confidence interval = -0.09 to 0.10). CONCLUSIONS: The correlation in time to pregnancy for monozygotic twins suggests genetic factors, although similarities in reporting behaviors could also be contributing to the correlation. The lack of correlation in time to pregnancy for dizygotic twins indicates that possible genetic factors of importance for fecundabililty are acting nonadditively. Hence, it may prove difficult to identify specific gene variants that influence fecundability on a population level if their effects depend on gene-gene interactions.     

Genetic and environmental causes of variation in renal tubular handling of sodium and potassium: a twin study

We have conducted a study of renal sodium and potassium reabsorption in 205 pairs of twins on freely chosen diets; 89 of the subjects were studied on more than one occasion. Renal tubular sodium and potassium handling, as measured by the fractional excretions FENa and FEK, show repeatable differences between individuals. Siblings (in this case monozygotic and dizygotic pairs of twins) are more alike in this respect than unrelated individuals. Comparison of monozygotic and dizygotic twin pairs indicates that genetic, rather than shared environmental, factors are probably responsible for this similarity, with heritability estimates of 0.5 for sodium and 0.6 for potassium. There are indications of sex differences in the sizes of the genetic and environmental effects for both variables and indications that the genetic effects may be qualitatively different for FEK. Such findings need further investigation.     

A comparison of genetic and environmental variance structures for asthma, hay fever and eczema with symptoms of the same diseases: a study of Norwegian twins

BACKGROUND: We compared patterns of genetic and environmental influences on variation in liability for asthma, hay fever and eczema with those for symptoms of the same diseases, and determined how common sets of genes and environmental factors contribute to the relationship between diseases and symptoms among Norwegian twins. METHODS: Analyses were based on self-reported asthma, hay fever and eczema and symptoms of the same diseases among 3334 pairs of Norwegian twins aged 18-35 years. Structural equation modelling was conducted to estimate the genetic and environmental variance structures. RESULTS: For all diseases the concordances and the twin correlations were higher among monozygotic than among dizygotic twins. The results of the modelling confirmed that genetic effects were substantial for the diseases, and were more moderate for symptoms. The phenotypic correlation between disease and symptom was 0.67 for asthma and wheeze (a/w), 0.64 for hay fever and sneeze (hf/s), and 0.54 for eczema and itch (e/i). Decomposition of these correlations into genetic (G) and environmental (E) pathways revealed that G = 0.48 and E = 0.19 for a/w, G = 0.40 and E = 0.24 for hf/s, and G = 0.34 and E = 0.20 for e/i. For the diseases, the specific sources of genetic variance accounted for more variation than the specific environmental variance. Variance decomposition revealed that specific sources of variance were primarily explained by genetic effects for diseases and by environmental influences for symptoms. CONCLUSIONS: Genetic effects account for greater variation in reported diseases than symptoms. Co-occurrence of diseases and symptoms is mainly explained by genetic effects common to both phenotypes, but non-shared environment is also important.     

Genetic and shared environmental influences on children's 24-h food and beverage intake: sex differences at age 7 y

BACKGROUND: The genetics of habitual food and beverage intake in early childhood is poorly understood. OBJECTIVE: The objective was to test the magnitude of genetic and environmental influences on 24-h food and beverage intake in 7-y-old children. The association between intake of specific food-beverage categories and child body mass index (BMI; in kg/m(2)) was also tested. DESIGN: A classic twin design was conducted, using the MacArthur Longitudinal Study of Twins. There were 792 children, including 396 boys from 102 monozygotic and 96 dizygotic twin pairs and 396 girls from 112 monozygotic and 86 dizygotic twin pairs; Children's 24-h dietary intake was estimated by parental recall, from which 9 composite food-beverage categories were derived. Height and weight were converted to BMI. Biometrical analyses of children's daily intake of food-beverage categories and BMI were conducted. RESULTS: There was consistent evidence of genetic influences on children's 24-h intake of food and beverages (servings/d), especially among boys. Seven categories showed significant heritability estimates among boys, ranging from 12% (fish and lemon) to 79% (peanut butter and jelly). Only 3 categories showed significant heritability estimates among girls, ranging from 20% (bread and butter) to 56% (fish and lemon). BMI showed a genetic correlation only with bread and butter intake in girls. CONCLUSION: The magnitude of genetic and environmental influences on children's 24-h food and beverage intake differed for boys and girls, which suggests sex differences in the development of eating patterns. Heritability estimates were generally large, although other eating phenotypes may be necessary for identifying genetic correlations with adiposity.