Twin study of genetic and environmental effects on lipid levels

A study of 106 pairs of monozygotic (MZ) and 94 pairs of dizygotic (DZ) twins tested the hypothesis that part of the previously described genetic influence on blood lipid levels can be ascribed to closer similarities among MZ than among DZ twin pairs in environmental factors that affect lipid levels. Participants were adult twin volunteers (age 17-66; 64 male and 136 female pairs) who were selected from the NH & MRC Twin Registry or were respondents to advertisements. They completed a 4-day weighed food diary from which mean nutrient intake was derived. Information on lifestyle and demographic variables was obtained by questionnaire and a nonfasting blood sample was taken for measures of total, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol and the HDL2 and HDL3 subfractions. Height and weight were measured, and body mass index (BMI) was calculated (kg/m2). Estimates of the heritability of sex-adjusted lipid levels were 0.72 for total cholesterol, 0.79 for HDL cholesterol, 0.69 for HDL2, 0.20 for HDL3, 1.06 for LDL cholesterol, and 0.44 for sex-adjusted BMI. In all cases except for HDL3, genetic variance was statistically significant. After adjusting for the effects of environmental variables in three different ways, the estimates of heritability were somewhat lower for total cholesterol, HDL2, and BMI, and those for HDL cholesterol (borderline) and LDL cholesterol (definitely) remained statistically significant but were decreased. A genetic influence on HDL3 was not found. Adjusted heritability estimates obtained from one method of analysis were 0.35 for total cholesterol, 0.49 for HDL, 0.04 for HDL2, -0.34 for HDL3, 0.66 for LDL, and 0.32 for BMI. These results suggest that the assumptions made in the classical twin study approach are not appropriate when examining genetic effects on lipid levels or BMI, or indeed on any biological variable that may be affected by environmental factors that tend to be more similar in MZ twins than in DZ twins. In these circumstances, more complex models may be needed to differentiate between genetic and environmental influences.     

青岛市成人双生子血脂相关指标的遗传度研究

目的了解成人双生子血清总胆固醇(TC)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、甘油三酯(TG)的水平及其遗传度。方法选择青岛市双生子库中316对18到60岁的健康成人双生子,用自动生化分析仪检测其空腹血清TC、HDL-C、LDL-C、TG的浓度。鉴定卵性后,用Mx软件拟合遗传模型,调整性别、年龄后,计算血脂相关指标的遗传度。结果双生子空腹血清TC、HDL-C、LDL-C、TG水平的均值分别为(4.52±1.08)、(1.46±0.39)、(2.58±0.79)、(1.11±0.77)mmol/L。Mx软件拟合结构方程模型结果显示,TC、HDL-C和LDL-C三项指标的最适模型为AE模型,其遗传度依次为53%、62%和57%。TG的最适模型为CE模型,遗传度为0。结论遗传因素和环境因素对TC、HDL-C和LDL-C的浓度都有重要影响,而TG主要受到环境因素的影响。     

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.     

Risk factors for atherosclerosis in twins

We performed multivariate genetic analyses of cardiovascular risk factors from two sets of data on US and Australian female twins. Similar models for body-mass index (BMI), serum low density (LDL) and high density (HDL) lipoproteins, including age as a covariate, were fitted successfully to both groups. These suggested that BMI, or genes responsible for a significant proportion of the variance of BMI, explained correlations between lipid subfractions, as well as those between blood pressure and lipid subfractions, especially HDL. © 1993 Wiley-Liss, Inc.     

Heritability of blood pressure in 7- to 12-year-old Chinese twins, with special reference to body size effects

Systolic and diastolic blood pressures and body-size indices such as body height, body weight, sitting height, chest circumference, skinfold thickness, and body mass index (BMI) were assessed in 110 pairs of like-sex Chinese twins (75 monozygotic and 35 dizygotic) aged 7-12 years. Significant correlations of blood pressure with body-size indices were found. Prior to adjusting for body-size effects, three twin methods yielded low heritability estimates for both systolic (0.32-0.41) and diastolic (0.32-0.51) pressures. Adjusting systolic pressure for body height and BMI via multiple regression nearly halved heritability estimates, but adjusting diastolic pressure for body height and skinfold thickness only changed the estimates slightly.     

Gender identity disorder and anorexia nervosa in male monozygotic twins

OBJECTIVE: Male identical twins with gender identity disorder (GID) in childhood and anorexia nervosa (AN) are presented. Etiologic aspects and the relationship among gender identity, sexual orientation, body dissatisfaction, and AN are discussed. METHOD: Case reports and a review of the literature are reported. RESULTS: In childhood, both twins showed an atypical gender behavior. Whereas one of the twins later developed a transsexual gender identity and asked for sex reassignment, the other developed a male identity but his appearance and clothing are effeminate. According to their biologic sex, they are concordant in regard to their homosexual orientation. In adolescence, both developed AN. Monozygotism was proved by DNA analysis. DISCUSSION: GID in childhood could be at least partly hereditary, whereas the development of the later phenotype of the gender identification is more determined by environmental factors. GID might be a risk factor for the development of AN.     

Finger-length ratios in female monozygotic twins discordant for sexual orientation

The second to fourth finger digit ratio (2D:4D ratio) is a sex-dimorphic characteristic in humans that may reflect relative levels of first trimester prenatal sex hormones. Low interdigital ratio has been associated with high levels of androgens. It has been reported in unrelated women that low 2D:4D ratio is associated with lesbian sexual orientation, but because of the nature of those samples, it was not possible to conclude whether lower ratio (and hypothetically, higher androgen levels) in lesbians are due to differences in genetics as opposed to differences in environment. To test the hypothesis that low 2D:4D in lesbians is due to differences in environment, interdigital ratio data were analyzed in a sample of female monozygotic (MZ) twins discordant for sexual orientation (1 twin was lesbian, the other was heterosexual; n = 7 pairs). A control group of female MZ twins concordant for sexual orientation (both twins were lesbian) was used as a comparison (n = 5 pairs). In the twins discordant for sexual orientation, the lesbian twins had significantly lower 2D:4D ratios on both the right and left hands than their heterosexual cotwins. There were no significant differences for either hand in the twins concordant for sexual orientation. Because MZ twins share virtually the same genes, differences in 2D:4D ratio suggest that low 2D:4D ratio is a result of differences in prenatal environment.     

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.     

3~7岁儿童气质遗传度双生子测评分析

目的 利用双生子人群估计3~7岁儿童气质的遗传度。方法 采用随机抽样法,通过Carey儿童气质问卷对131对3~7岁双生子气质进行测评。对测评结果进行结构方程模型拟合,估算各气质维度的遗传度。结果 3~7岁儿童气质类型的遗传度为45.96%;特殊环境因素对气质维度的影响（方差为4%~36%）具有普遍性,除趋避性、坚持性和男童活动水平外,其他气质维度均存在共同环境效应（方差为13%~65%）,年龄效应方差（0%~8%）则不明显;校正年龄后,活动水平、节律性、趋避性、适应性、反应强度、情绪本质、坚持性、注意分散度及反应强度的遗传度分别为：男童35.83%、46.55%、82.67%、64.91%、45.09%、44.00%、83.95%、64.93%、40.88%;女童81.14%、21.66%、82.67%、80.39%、67.28%、44.00%、83.96%、64.93%、40.88%。结论 3~7岁儿童气质受遗传与环境因素的共同影响,男女节律性、情绪本质、反应阈、男童活动水平与反应强度可能更多受环境因素的影响。     

不同发育期双生子皮褶厚度及体成分分析

目的 分析遗传与环境因素不同发育期双生子皮褶厚度及体成分的作用特点。方法 测量376对6～18岁同性别双生子(同卵245对,异卵131对)肱三头肌、肩胛下皮褶厚度,用长岭和Brozek公式估算体成分;用Mx软件拟合最佳模型,计算各指标遗传与环境方差组分,分析年龄、性别和不同发育期的作用。结果 全部双生子分性别校正年龄后,各指标遗传度在0.59～0.87之间;不同发育期各指标遗传度存在差异,肱三头肌皮褶、肩胛下皮褶、2处皮褶厚度之和、体脂百分比的遗传度男生在青春期前期最低,分别为0.55,0.62,0.53,0.51,女生在青春期晚期最低,分别为0.53,0.43,0.24,0.40;男、女瘦体重遗传度随青春期发育进程呈增加趋势。结论 遗传因素对儿童青少年皮褶厚度和体成分起主要作用,但年龄、性别和不同发育阶段对其也有一定影响。     

3～6岁双生子体型遗传分析

目的分析3～6岁幼儿体型各因子的遗传度,探讨遗传与环境因素对其体型发育的影响。方法采用Heath-Carter体型法对72对3～6岁同性别双生子[同卵双生子(MZ)42对,异卵双生子(DZ)30对]的体型进行分析,用Holzinger公式估算体型各因子遗传度。结果二维空间的体型离散距离(SDD)和三维空间体型位置距离(SAD)显示,MZ的体型较DZ更为接近;体型各因子对间方差在2类双生子间均无明显差异,中因子和外因子的对内方差DZ均明显大于MZ、组内相关系数MZ均明显大于DZ;内、中、外3个因子的遗传度分别为0.38、0.67、0.73。结论遗传与环境因素对3～6岁幼儿体型发育均有一定影响,内因子主要受环境影响,中、外因子受遗传因素影响较大。     

青岛市成人双生子吸烟饮酒遗传度分析

目的分析遗传因素对双生子吸烟、饮酒的影响。方法以青岛地区自愿参加本研究的年龄≥24周岁的双生子为对象，在卵型鉴定的基础上。采用Holzinger方法分析其吸烟、饮酒的遗传度。结果估计吸烟的遗传度为（66．5±5．53）％，重度吸烟的遗传度为（43．0±5．75）％。男性同卵双生子在吸烟行为上Kappa一致性检验K=0．453，P〈0．001。异卵双生于K=0．307，P=0．005；饮酒的遗传度为（60．8±7．79）％，大量饮酒的遗传度为（22．2±9．80）％。男性同卵双生于在饮酒行为上Kappa一致性检验K=0．518。P〈0．001，异卵双生子K=0．160，P=0．224。结论吸烟、饮酒受遗传因素影响较大；重度吸烟、大量饮酒受遗传因素影响较小。男性同卵双生子在吸烟、饮酒行为上呈现中度一致性．男性异卵双生子、女性双生子一致性差异无统计学意义。     

Differential heritability of eating attitudes and behaviors in prepubertal versus pubertal twins

OBJECTIVE: Differential heritability of eating pathology in prepubertal, pubertal, and 17-year-old twins was examined using a population-based twin sample. METHOD: Participants included 530 11-year-old (452 prepubertal, 78 pubertal twins) and 602 17-year-old female twins from the Minnesota Twin Family Study. Puberty was assessed with the Pubertal Development Scale, and general eating pathology was assessed with the total score from the Minnesota Eating Disorders Inventory (M-EDI). RESULTS: M-EDI total score intraclass correlations for the pubertal 11-year-old group were more similar to the 17-year-old twins' than the prepubertal 11-year-old twins, suggesting similar levels of genetic influence in the pubertal and older adolescent cohort. Model-fitting corroborated these impressions, indicating that genetic factors accounted for 0% of the variance in 11-year-old prepubertal twins but 54% of the variance in 11-year-old pubertal and 17-year-old twins. DISCUSSION: Findings suggest that a portion of the genetic influence on eating pathology may become activated during puberty.     

血压的遗传度分析

目的利用双生子资料探讨不同年龄组血压的遗传度的大小。方法在1999年大面积的横断面调查中,收集8岁及以上的双胞胎1101对,主要来自安庆的四县一郊,经统一调查表收集双生子的人口学及各种环境因素和职业暴露情况,用水银柱式血压计测量血压。结果对血压值经典的Holziger方法进行血压的遗传度分析,按年龄分层后儿童青少年血压的遗传度较低,总体研究对象的SBP的遗传度为0.278,DBP的遗传度为0.368.异卵双生子的对内差大于同卵双生子,差别达到显着性水平,且随着年龄的增加,差值增加。结论遗传因素是影响血压的重要因素。     

Genotypic and phenotypic similarities in pulmonary function among family members of adult monozygotic and dizygotic twins

Population studies have demonstrated that obstructive airways disease aggregates within families. The authors used a twin family model of analysis to estimate the genetic and environmental influences on pulmonary function. A total of 1,635 members of 414 families of adult twins (252 monozygotic, 162 dizygotic) enrolled in the Greater Boston Twin Registry were studied between 1981 and 1982. Correlations in levels of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), adjusted for age, sex, height, and current smoking status, were compared among 16 groups of relatives sharing various degrees of genetic relatedness. A direct relation between shared genotype and the magnitude of the familial correlations for pulmonary function was observed. For FEV1, the correlations were 0.71 for monozygotic twins (100% shared genotype), 0.16 to 0.29 for relatives with 50% shared genotype, 0.09 to 0.27 for relatives with 25% shared genotype, 0.06 for cousins with 12.5% shared genotype, and -0.14 to 0.14 for unrelated family members. Correlations for FVC were similar. Stratification of the analysis by concordance or discordance for passive tobacco smoke exposure or for frequency with which families visited one another did not systematically alter these relations. These data suggest that phenotypic similarities in pulmonary function relate directly to genetic similarities, and are consistent with a multifactorial mode of inheritance.     

A pair of monozygotic twins discordant for homosexuality: Sex-dimorphic behavior and penile volume responses

In reports of identical twins discordant for homosexuality, the homosexual twins showed the effeminacy syndrome in childhood. This has been considered evidence that the homosexuality comes from the twin himself. The possibility that the heterosexual twin was denying homosexuality has never been excluded. A pair of identical male twins discordant for homosexuality are reported. They showed significant differences in their penile volume responses to moving pictures of male and female nudes indicative of sexual orientations consistent with their statements. The homosexual twin showed the effeminacy syndrome. Aspects of the syndrome can be induced in mammals by altering their hormonal environment during some critical period in their intrauterine development. Discordance for homosexuality in identical twins could be due to one's being exposed to a different hormonal level during such a critical period.     

青岛市成人双生子体型指征的遗传度研究

目的探讨遗传因素对体质指数(BMI)和腰臀围比值(WHR)等体型指征的影响程度。方法青岛地区自愿参加本研究的496对24周岁及以上的双生子。在卵型鉴定的基础上。应用Mx软件构建结构方程模型分析遗传度。结果估计体质指数的遗传度为76％，男、女性分别为33％，74％；腰臀围比值的遗传度为62％，男、女性分别为0．12％，74％。结论在体型指征的相关指标中，BMI和WHR均受遗传因素影响较大。其中，女性的BMI和WHR受遗传因素的影响可能大于环境因素；男性体质指数受环境因素影响大于遗传因素，腰臀围比值则可能不受遗传因素影响。     

体外受精-胚胎移植术形成单卵双胎因素Meta分析

目的 采用Meta分析方法研究体外受精-胚胎移植治疗中影响单卵双胎发生的相关因素。方法 利用计算机检索Cochrane图书馆、PubMed、Web of science、中国知网、维普、万方各数据库对截止2020年2月1日所有公开或未公开发表的中英文文献。制定纳入、排除标准,剔除不符合要求的研究,对不同治疗方式、囊胚移植及新鲜冻融胚胎移植导致的单卵双胎率进行meta分析。结果 分别比较在IVF-ET和ICSI(OR=0.66,95%CI为0.49~0.90,P=0.008）导致的单卵双胎发生率有统计学意义,新鲜胚胎移植周期和冻融胚胎移植周期(OR=0.92,95% CI为0.72~1.17,P=0.474）、FET周期中卵裂期和囊胚期(OR=0.88,95% CI为0.58~1.35,P=0.563）导致的单卵双胎率无统计学差异。结论 行ICSI技术造成单卵双胎率高于行IVF操作;囊胚期胚胎移植不增加MZT的风险。     

童年中期双生子下肢长相关指标的遗传学分析

目的分析遗传与环境因素对童年中期双生子儿童下肢长相关指标的影响,并分析其中年龄和性别的作用。方法对呼和浩特市和包头市5~8岁171对双生子儿童下肢长相关指标进行测量,使用Mx软件拟合最佳模型,计算校正年龄前后各指标遗传与环境方差组分。结果各指标最佳拟合模型均为ACES,校正年龄后遗传度分别为:身高:男43%,女60%);坐高:男62%,女62%;下肢长:男50%,女62%;下肢长指数:男18%,女36%。身高、下肢长和下肢长指数的遗传度存在一定性别差异。结论童年中期下肢长相关指标发育受环境因素的影响较大,应通过加强营养与锻炼及控制相关疾病等改善下肢长度发育,促使儿童生长发育潜力得到更好的发挥。