双生子儿童贫血状况分析

目的通过分析双生子儿童贫血状况和贫血同病率,探讨其遗传和环境效应.方法选取5～19岁双生子228对,其中MZ(单卵双生子)142对,DZ(二卵双生子)86对,在DNA卵性鉴定基础上,以成对法计算同病一致率、调整BMI前后组内相关系数及遗传度.结果双生子儿童贫血检出率与一般人群无明显差异,贫血同病一致率分别为MZ 0.28,DZ 0.15,Hb(血红蛋白)遗传度为0.23.调整BMI前后MZ与DZ组内相关系数和遗传度无显著变化.结论儿童贫血状态受遗传及环境因素共同影响,环境效应更明显.     

Male factor infertility: a twin study

There is a considerable body of literature on the causes of female infertility, but far less is known about male factor infertility. We conducted a classical twin study to estimate the genetic influence on 12-month male factor infertility. The study used the Vietnam Era Twin (VET) Registry, which includes male twin pairs born between 1939 and 1957, and who served in the US military between 1965 and 1975. In 1987, a health survey was mailed to all twins and obtained a 74% response rate. The current analyses comprised 1795 complete pairs in which both twins were married only once. Proband-wise concordance rates, tetrachoric correlations, and a bivariate probit model were used to calculate estimates of familial clustering and heritability for male factor infertility. The proband concordance rate for male factor infertility was 38% [95% CI 32.8, 42.4] in monozygotic (MZ) pairs and 33% [95% CI 28.0, 38.6] in dizygotic (DZ) pairs. The tetrachoric correlations for male infertility were 0.15 in MZ and 0.04 in DZ pairs. This pattern provides evidence of familial clustering, although genetic influence was not evident (P = 0.21). The current study identified that 12-month male factor infertility clustered within families. However, results suggest that factors unique to individual twins may play a more prominent role in male infertility than additive genetic effects or the common environment.     

Concordance for mortality with special reference to ischaemic heart disease and cerebrovascular disease: A Study on the Swedish Twin Registry

The Swedish Twin Registry contains about 11 000 same-sexed twin pairs born between 1886 and 1925 with both members alive when the registry was formed in 1961. During the years 1962 to 1973, 2780 deaths occurred. 727 deaths were due to ischaemic heart disease (IHD), 345 due to cerebrovascular disease (CVD), and 727 due to cancer. The rate of concordance for the whole twin population revealed a significantly (p < 0.05) higher concordance rate for IHD among the male monozygotic (MZ) pairs as compared to the dizygotic (DZ) pairs (15.8% versus 8.0%). The corresponding figures for the female pairs were 11.0% (MZ) and 7.5% (DZ), respectively. With regard to death in CVD and cancer, the rates of concordance were about the same for MZ and DZ pairs in both males and females. When subgrouping was made for age groups, the difference in concordance rate for IHD in males was still more pronounced for the younger age group, born 1901–1925, (16.1% versus 5.4%). These data may indicate the existence of a genetic determination on death in IHD, especially in males, whereas a genetic determination on death in CVD and cancer seems more uncertain.     

Plasma cholesterol variation in the National Heart, Lung and Blood Institute Twin Study

Plasma cholesterol was measured in the fifth decade of the life of 249 pairs of monozygotic (MZ) and 262 pairs of dizygotic (DZ) World War II veteran twins and 70% of the same cohort 10 years later. There were no significant differences between the mean cholesterol values for MZ and DZ twins, and the within DZ pair mean squares were significantly larger than the within MZ pair mean squares for all of the cholesterol variables measured. However, the DZ twins were found to have greater total variance, positive skewness, and leptokurtosis than the MZ twins for total and high-density lipoprotein cholesterol, and the total/high-density ratio. Comparisons with published data revealed that the variance of DZ twins was similar to that of singletons while the MZ twins have smaller total variance, perhaps owing to a missing component of variation. Hypotheses for the source of the differences in the zygosity distributions are proposed including environmental influences (pre- or post-natal and within- or among-families), genetic differences, and selection at the time of induction into the armed services. Because of the differences in total variance of the two zygosities it is difficult to know which estimates of genetic variance or heritability have the least bias. However, these data provide clues that may lead to further understanding of sources of plasma cholesterol variation that could be important to the future understanding of risk for coronary heart disease.     

Likelihood-based concordance tests for analysis of ascertained twin pair multinomial data

The classic twin model design has a wide application in human genetics. Under the assumption that nongenetic effects are shared to the same degree by monozygotic (MZ) and dizygotic (DZ) twin pairs, a test of the equality of casewise concordances between MZ and DZ twins provides a clue to the influence of genetic and environmental factors on a disease. The casewise concordance is the conditional probability that given that one member of a twin pair is affected, the other is also affected. When disease prevalence is low or cost-effectiveness is considered, collection of twin pairs by ascertainment for performing casewise concordance analysis is required. In this article, by defining an overall casewise concordance parameter, several likelihood-based tests, such as likelihood ratio test LR, score test Score, the usual Wald test Wald and an alternative Wald test WaldA are investigated for a test of the equality of concordances between ascertained MZ and DZ twin pairs under multinomial models. Simulation studies were conducted for data with small sample sizes. The results show that the type I error rates and power of LR and Score are stable only when the overall casewise concordances are not extremely small or large. The Wald has higher power performance in most cases but would slightly inflate type I error rates; the WaldA is the most robust and recommended approach.     

Concordance of ischemic heart disease in the NHLBI twin study after 14-18 years of follow-up

Morbidity and mortality were assessed in the NHLBI twin study at the end of 1987. Deaths were greater in DZ twins (58/520, 11.2%) than MZ twins (38/508, 7.5%). Ischemic heart disease concordances were 2.3 times higher in MZ pairs and 2.8 times higher in DZ pairs than expected based on the prevalence of ischemic heart disease in the cohort. Family history scores for heart disease, calculated 14-18 years earlier at entry to the study, were significantly higher in DZ pairs where one or both members later developed ischemic heart disease and in corcordant MZ pairs than in twin-pairs without any subsequent heart disease. Concordance rates were not significantly different between MZ and DZ pairs. The results agree with previous suggestions that selection at enlistment into the armed services over 40 years ago, as well as later volunteering for the NHLBI twin study, resulted in a decline in the number of concordant MZ pairs.     

Twins, smoking and mortality: a 12-year prospective study of smoking-discordant twin pairs

Despite the increasing scientific evidence for a causal role of tobacco smoking in lung cancer and coronary heart disease, critics, several decades ago, put forward an alternative hypothesis. The constitutional hypothesis has stated that there are genetic or other common factors, which predispose both to smoking and disease, but that the two are not causally related. A critical test of this hypothesis is the study of disease in monozygotic (MZ) twin pairs in which one smokes and the other never has. Earlier twin studies found only small differences in the mortality of smoking and nonsmoking twins of discordant pairs. In the Finnish Twin Cohort, a population-based panel of adult like-sexed twin pairs, a questionnaire study carried in 1975 permitted identification of twin pairs discordant for cigarette smoking. The nonsmoking cotwins had never been regular smokers. The smoking twins were divided into 1278 current smokers [CS; 143 MZ and 598 dizygotic (DZ) males and 171 MZ and 585 DZ females] and 1210 former smokers (FS; 129 MZ and 408 DZ males and 113 MZ and 341 DZ females). Exposure to tobacco was much higher among males; over 25% of men smoked 20 or more cigarettes daily compared to less than 10% of women. Follow-up of mortality yielded data on time and cause of death. Analyzing on first deaths from concordant pairs, there were 13 deaths in the smokers of male CS MZ pairs and 1 death in the nonsmoking cotwins (relative risk = 13.0, P less than 0.01). Excess mortality was also found for male CS DZ smokers (RR = 2.43, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Disease concordance and sex similarity in twins

Disease patterns in twins may show the presence of genetic or of environmental causes. Two arguments of inference have been used. Discordances between monozygotic twins have been taken to indicate the presence of environmental determinants; and high levels of concordance in monozygotic (MZ) pairs compared with dizygotic (DZ) pairs have been taken to indicate the presence of genetic causes. Neither argument is rigorous and, at this level, neither is quantitative.     

中国成年双生子饮茶行为分布特征

目的 描述中国双生子登记系统（CNTR）成年双生子饮茶行为的分布特征,探索饮茶行为在双生子人群中的分布规律,为探究遗传和环境因素对饮茶行为的影响提供线索。方法 样本选自2010-2018年在CNTR进行登记的双生子,纳入≥18岁且具有饮茶信息的双生子共25 264对进行分析,描述双生子中饮茶行为的人群、地区分布特征,以及不同卵型双生子饮茶行为一致率和对内饮茶量差异分布情况。结果 研究对象年龄（35.38±12.45）岁,每周饮茶者占比17.0%,饮茶量（3.36±2.44）杯/d。男性、50~59岁、南方、城镇、文化程度高、双生子中先出生的个体中每周饮茶者比例较高（P<0.05）,未婚者中比例较低（P<0.001）。双生子对内分析发现同卵饮茶行为一致率均大于异卵,饮茶遗传度为13.45%（11.38%~15.51%）,除女性亚组外,不同性别、年龄、地区间饮茶一致率差异有统计学意义（均P<0.05）;根据性别、年龄、地区分层后仅男性同卵一致率始终呈大于异卵趋势。同性别双生子对内饮茶量差异在男性中呈现同卵小于异卵的特征（P<0.05）,而女性中差异不明显。结论 本研究双生子人群饮茶行为的分布存在人群和地区差异,饮茶行为主要受环境因素影响,遗传因素影响较弱,且遗传效应大小在不同性别、年龄、地区间不尽相同,性别可修饰这一遗传作用。     

Early-life environment influencing susceptibility to cytomegalovirus infection: evidence from the Leiden Longevity Study and the Longitudinal Study of Aging Danish Twins

Human cytomegalovirus (CMV) is a common herpesvirus establishing lifelong persisting infection, which has been implicated in immunosenescence and mortality in the elderly. Little is known about how and when susceptibility to CMV infection is determined. We measured CMV seroprevalence in two genetically informative cohorts. From the Leiden Longevity Study (LLS) we selected long-lived sib-pairs (n=844) and their middle-aged offspring and the offspring's partners (n=1452). From the Longitudinal Study of Aging Danish Twins (LSADT) 604 (302 pairs) same-sex monozygotic (MZ) and dizygotic (DZ) twins aged 73-94 years were included (n=302 pairs). Offspring of the long-lived LLS participants had significantly lower seroprevalence of CMV compared to their partners (offspring: 42% vs. partners: 51%, P=0·003). Of 372 offspring living with a CMV-positive partner, only 58% were infected. The corresponding number for partners was 71% (P<0·001). In the LSADT, MZ and DZ twins had high and similar CMV-positive concordance rates (MZ: 90% vs. DZ: 88%, P=0·51) suggesting that shared family environment accounts for the similarity within twin pairs. Our findings suggest that susceptibility to CMV infection--even under continuous within-partnership exposure--appears to be more strongly influenced by early-life environment than by genetic factors and adult environment.     

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.     

双生子A型人格与高血压及血生化指标研究

目的 了解双生子A型人格与高血压及血液生化指标的关系。方法 利用遗传流行病学方法对青岛市89对24岁以上双生子(同卵55对，异卵34对)进行调查。并进行A型人格测试，以比较同卵与异卵双生于A型人格得分的相关程度、A型人格及血压的一致性。推测遗传与环境因素对A型人格的影响，A型人格与高血压的关系，并探讨血液生化指标与A型人格的关系。结果 经KAPPA一致性检验，同卵(MZ)双生子之间A型人格存在着显的一致性(P＜0．001)，而异卵(DZ)双生子之间的一致性无显性差异(P＝0．802)。同时，MZ双生子之间A型人格和血压也存在显的一致性(P＜0．001)，而DZ双生子之间A型人格和血压无明显一致性(P＝0．102)。有A型人格的双生子血压的收缩压明显高于非A型人格的双生子(P＜0．05)。许多生化指标与A型人格因素相关，但是所计算出的相关系数大都小于0．30，属于弱相关。结论 MZ双生子A型人格及高血压之间存在着显的一致性，而这种一致性在DZ双生子表现不明显。A型人格是高血压的危险因素之一。A型人格与所研究血液基本生化指标之间相关较弱。     

Basal metabolic rate in monozygotic and dizygotic twins

The basal metabolic rate (BMR) was determined in 14 pairs of monozygotic (MZ; 11 females, 3 males) and 12 pairs of dizygotic (DZ; 10 females, 2 males) twins, with mean ages of 22.7 and 26 years. Zygosity was confirmed using DNA fingerprinting. When BMR was expressed as kJ/d, kJ/kg/d and kJ/kg FFM/d significant intra-class correlation coefficients were observed in the MZ twins of 0.82, 0.79 and 0.85, respectively. The DZ twins showed much lower intra-class correlations coefficients of 0.1, 0.07 and -0.04. Although the results of the study suggest a likely genetic component to the variation in BMR, they should be interpreted with caution as heritability estimates vary with the method of calculation. These will be critically discussed in the paper.     

Genetic Contribution to Suicidal Behaviors and Associated Risk Factors among Adolescents in the U.S.

This paper examines genetic contribution to suicidal behaviors and other risk factors associated with suicidal behavior among adolescents in the U.S. Using adolescent twin data in the National Longitudinal Study of Adolescent Health (N=1448), we compared concordance in suicidal ideation and attempt among monozygotic (MZ) and dizygotic (DZ) twins. Heritability of risk factors for suicidal behaviors also was examined using Pearson correlation and mixed-model analyses. A trend of higher concordance in suicidal ideation and attempt was found among MZ than DZ twins but the difference was not statistically significant by the stringent test of bootstrapping analysis. Evidence of heritability was found for several suicide risk factors. The percentage of variance explained by heritability was larger among female twins for depression, aggression, and quantity of cigarettes smoked in comparison to heritability estimates for male twins. However, estimated heritability was larger among male than female twins for alcohol use and binge drinking. Heritability influence was negligible among both sexes for other drug use. Risk factors for suicidal behaviors among adolescents may be heritable. Gender differences found in the heritability of some suicide risk factors suggest these genetic contributions are gender specific. Future research examining potential interactions between expression of genetic influence and particular environmental contexts may enhance prevention and intervention efforts.     

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.     

Intrapair comparisons of diet and food preference in adult twins

OBJECTIVES: An investigation was conducted on the influence of genetic and lifestyle factors related to the determination of eating behavior of human beings. The objective was to obtain information about lifestyle factors that may help health professionals intervene in terms of the prevention of diet-related diseases. METHODS: The subjects were 180 pairs of adult twins aged over thirty, comprising of 134 monozygotic (MZ) and 46 dizygotic (DZ) pairs. Every subject was given an interview concerning dietary habits, food preference, food intake, as a part of medical examination. The intake of food containing salt and fat, the intake of food meals, the frequency of daily meals, and the frequency of eating 18 sorts of food were assessed on an individual basis, with a questionnaire on nutrition. The expected and observed values of intrapair concordance rates were calculated, and compared within each zygosity, using the chi-square test. RESULTS: Significant differences between the expected and observed for intrapair concordance rates were shown with monozygotic twins, regarding every category of question. Comparing MZ pairs who had lived apart before their twenties with the other MZ pairs, the latter had a tendency to show significant differences between the expected and observed values of intrapair concordance rate, regarding every category of question. In each case, the observed values were higher than the expected values. CONCLUSIONS: The study implied that both genetic and lifestyle factors influence the determinants of eating behavior of human beings. This finding shows the importance of understanding individual characteristics of food preference and eating behavior for intervention regarding lifestyle factors for prevention of diet-related diseases.     

The heritability of smoking behaviour in pregnancy, and the birth weights of offspring of smoking-discordant twins

Questionnaire information on smoking habits in pregnancy was collated in 341 monozygotic (MZ) and 321 dizygotic (DZ) female twin pair cases from a population-based Norwegian Twin Panel. In a multifactorial model, the intra-pair correlation in smoking was 0.797 (+/- 0.042) in monozygotic (MZ) and 0.443 (+/- 0.075) in dizygotic (DZ) twin pairs, indicating a substantial genetic influence on liability to smoke in pregnancy. The questionnaire information was linked with birth records in the Medical Birth Registry of Norway, and birth weights of offspring of 62 MZ and 100 DZ smoking-discordant twin pairs were studied. Offspring of smoking MZ twins weighed 127 g less than birth order matched offspring of the non-smoking co-twins. This finding is additional evidence that smoking is a direct cause of reduced birth weight in offspring.     

The association between body height and coronary heart disease among Finnish twins and singletons

OBJECTIVE: An inverse association between body height and the incidence of coronary heart disease (CHD) has been observed. However, the mechanisms behind this association are still largely unknown. We will examine the role of genetic and familial factors behind the association in a large twin data set. DESIGN AND SETTING: The data were derived from the Finnish Twin cohort including 2438 singletons, 4073 monozygotic (MZ) twins, and 9202 dizygotic (DZ) twins aged 25-69 years at baseline in 1976. Incident CHD cases were derived from hospital discharge data and cause of death data between 1977 and 1995. Cox regression analysis and conditional logistic regression analysis were used. RESULTS: In population-level analyses no differences in the general risk of CHD between zygosity groups were found. The association between body height and CHD was similar between sexes and zygosity groups. When men and women in all zygosity groups were studied together an increased risk of CHD was found only among the shortest quartile (hazard ratio [HR] = 1.34, 95% CI: 1.14-1.57). Among the twin pairs discordant for CHD a suggestive increased risk for the shorter twin was seen among DZ twins (odds ratio [OR] = 1.19, 95% CI: 0.95-1.48) when men and women were studied together. CONCLUSION: An inverse association between body height and CHD was broadly similar between sexes and twin zygosity groups and was associated with short stature. Among discordant twin pairs we found a weak association among DZ twins but not MZ twins. This may suggest the role of genetic liability behind the association between body height and CHD.     

遗传与环境因素对女性青春期性征发育的影响

目的探讨遗传与环境因素对女性青春期性征发育的影响,为进一步深入研究女性青春期发育提供依据。方法以学校登记为基础,募集6~18岁女性双生子180对,其中单卵双生(MZ)132对,二卵双生(DZ)48对,按Tanner标准进行青春发育分期,询问有无月经初潮及月经初潮年龄。结果乳房开始发育的年龄为9~12岁,阴毛开始发育的年龄集中在9~13岁,月经初潮年龄多集中在11~13岁。月经初潮、性征发育一致率均为MZ>DZ,月经初潮的遗传指数为0.71,乳房和阴毛发育的遗传指数分别为0.34,0.45。月经初潮年龄的组内相关系数MZ>DZ(P<0.001),偶内均方MZ相似文献