Dizygotic twinning is not associated with methylenetetrahydrofolate reductase haplotypes

BACKGROUND: Folate metabolism is critical to embryonic development, influencing neural tube defects (NTD) and recurrent early pregnancy loss. Polymorphisms in 5,10-methylenetetrahydrofolate reductase (MTHFR) have been associated with dizygotic (DZ) twinning through pregnancy loss. METHODS: The C677T and A1298C polymorphisms in MTHFR were genotyped in 258 Australasian families (1016 individuals) and 118 Dutch families (462 individuals) of mothers of DZ twins and a population sample of 462 adolescent twin families (1861 individuals). Haplotypes were constructed from the alleles, and transmission of the MTHFR haplotypes to mothers of DZ twins and from parents to twins in the adolescent twin families analysed. RESULTS: The C677T and A1298C were common in all three populations (frequencies > 0.29). There was strong linkage disequilibrium (D' = 1) between the variants, showing that specific combinations of alleles (haplotypes) were transmitted together. Three haplotypes accounted for nearly all the variation. There was no evidence of any association between MTHFR genotype and twinning in mothers of twins, or of the loss of specific MTHFR genotypes during twin pregnancies. CONCLUSIONS: It is concluded that variation in twinning frequency is not associated with MTHFR genotype.     

Multiple gestations: timing of indicated late preterm and early-term births in uncomplicated dichorionic, monochorionic, and monoamniotic twins

In this work we review the indications for late preterm and early-term birth in uncomplicated dichorionic, monochorionic, and monoamniotic twin gestations. Uncomplicated dichorionic twins have optimal outcomes when delivered at 38 weeks' gestation. Monochorionic twins, however, are at greater risk for unexpected stillbirth, and a management plan of late preterm delivery (34-37 weeks) after informed consent is reasonable. Monoamniotic twins are at even greater risk for sudden intrauterine fetal demise, and it is recommended that these expectant mothers be managed by inpatient hospitalization with fetal testing 1-3 times per day and delivery between 32 and 34 weeks' gestation. Recommendations are also provided for the circumstance of single intrauterine fetal demise in a twin gestation.     

The Direction of Longitudinal Associations Between Sleep Problems and Depression Symptoms: A Study of Twins Aged 8 and 10 Years

Study Objectives:

To establish the direction and etiology of longitudinal associations between sleep problems and depression symptoms in children.

Design:

Data on twins aged 8 and 10 years were obtained. At assessments, parents completed the Child Sleep Habits Questionnaire, and twins completed the Children''s Depression Inventory.

Setting:

Participants were mainly interviewed at the Institute of Psychiatry, London.

Patients or Participants:

Three hundred twin pairs initially enrolled in the study.

Interventions:

N/A.

Measurements and Results:

A genetically informative cross-lagged model examined links between sleep and depression. Sleep problems at age 8 predicted depression at age 10 (partial regression coefficient [95% confidence intervals] = 0.10 [0.01-0.18]). The converse was not found. Stability of sleep problems across time was mainly due to genes (46% of the genetic influence on sleep at 10 was due to the same genetic influence on sleep aged 8). Stability of depression was mainly due to nonshared environmental influences (19% of the nonshared environmental influence on depression at 10 was due to the same nonshared environmental influence on depression at age 8). The cross-lagged association between sleep problems at 8 and depression at 10 years was largely due to genes, although this finding was nonsignificant.

Conclusions:

This study adds to our understanding of the temporal precedence of sleep problems and depression and the risks underlying their associations. There are implications regarding the value of specifying genes linked to sleep problems and potential opportunities for informing early intervention strategies in high-risk groups at key points in the progression to developing more serious problems.

Citation:

Gregory AM; Rijsdijk FV; Lau JYF; Dahl RE; Eley TC. The direction of longitudinal associations between sleep problems and depression symptoms: a study of twins aged 8 and 10 years. SLEEP 2009;32(2):189–199.     

儿童青少年智力的双生子研究

目的 应用双生子法探讨遗传和环境因素对儿童青少年智力影响.方法 采用中国修订版-韦氏儿童智力量表评定6～16岁333对双生子的智力特点.应用结构方程模型分析遗传和环境因素对智力的影响.结果 6～16岁儿童青少年的总智商(intelligence quotient,IQ)遗传度为0.43,其中言语智商(verbal intelligence quotient,VIQ)遗传度为0.37,而遗传因素对操作智商(performance intelligence quotient,PIQ)影响甚小.10～16岁的青少年智力遗传度大于6～9岁的儿童(IQ:0.82 vs 0.00,VIQ:0.80 vs 0.00,PIQ:0.51 vs 0.00).男性的言语智商(0.47)受遗传影响大于女性(0.05);而在男性和女性中,操作智商均主要受共享环境的影响.结论 在儿童青少年时期,总智商和言语智商有中度的遗传度,而共享环境因素对操作智商的影响更大;但智商总分及言语智商和操作智商分测试分在年龄较大的青少年的遗传度都明显高于年龄较小的儿童.     

Pregnancy and perinatal outcomes of first-trimester crown−rump length discordant IVF dichorionic twin pregnancies – a retrospective cohort study

Research QuestionThis study aimed to evaluate the association between discordance in crown–rump length (CRL) and adverse pregnancy and perinatal outcomes in dichorionic twin pregnancies.DesignThis was a retrospective cohort study of dichorionic twin pregnancies after IVF that showed two live fetuses at the first ultrasound scan between 6 ⁺⁵ and 8 weeks gestational age from 1 January 2015 to 31 December 2016. Study groups were defined by the presence or absence of 20% or more discordance in CRL. The primary outcomes were early fetal loss of one or both fetuses before 12 weeks and birthweight discordance. Secondary outcomes included fetal anomalies, fetal loss between 12 and 28 weeks, stillbirth, small for gestational age (SGA) at birth, low birthweight (LBW), very low birthweight (VLBW), admission to the neonatal intensive care unit (NICU) and preterm delivery (PTD).ResultsCRL-discordant twin pregnancies were more likely to end in the loss of one fetus before 12 weeks’ gestation (odds ratio [OR] 15.877, 95% confidence interval [CI] 10.495–24.019). Discordant twin pregnancies with twin deliveries had a significantly higher risk of birthweight discordance (OR 1.943, 95% CI 1.032–3.989). There was no significant difference in perinatal outcomes including fetal anomalies, PTD, LBW, VLBW, SGA, neonatal death and admission to NICU between singleton or twin deliveries.ConclusionsDiscordant twin pregnancies were at increased risk of one fetal loss prior to 12 weeks’ gestation. Except for birthweight discordance, there was no significant difference between CRL discordance and other adverse perinatal outcomes.     

Adolescence and risk of preterm birth in multifetal gestations

Objective: The objective of this study is to evaluate if adolescence confers additional risk for preterm delivery in multifetal gestations.

Methods: This is a retrospective review of all twin and triplet deliveries from 8/2008 to 12/2012 at two Detroit Hospitals. Outcomes in adolescent mothers aged 19 or younger (n?=?59) were compared with adult controls aged 20–34 (n?=?350).

Results: Mean gestational age at delivery in adolescents was 31.3 (SD: 5.8) weeks versus 34.2 (SD: 4.3) weeks in adults (p?p?=?.02) and early-preterm delivery (aOR, 2.2; 95% CI 1.2–4; p?=?.01). Adjusted rates of preterm and early-preterm delivery were markedly higher in adolescents compared with controls. Being an adolescent was also a significant risk factor for iatrogenic preterm delivery (aOR, 2.4; 95% CI 1.1–5.5; p?=?.04).

Conclusions: Adolescents pregnant with twins or triplets deliver 3 weeks, on average, before adults and are at markedly increased risk of preterm and early-preterm delivery.     

Large,Consistent Estimates of the Heritability of Cognitive Ability in Two Entire Populations of 11-Year-Old Twins from Scottish Mental Surveys of 1932 and 1947

Twin studies provide estimates of genetic and environmental contributions to cognitive ability differences, but could be based on biased samples. Here we report whole-population estimates using twins from unique mental surveys in Scotland. The Scottish Mental Surveys of 1st June 1932 (SMS1932) and 4th June 1947 (SMS1947), respectively, administered the same validated verbal reasoning test to almost everyone born in 1921 or 1936 and attending school in Scotland. There were 572 twin pairs from the SMS1932, and 517 pairs from the SMS1947. Information on zygosity was unavailable. A novel application of a mixture distribution was used to estimate genetic and environmental components of verbal reasoning variation by maximum likelihood. We found consistent heritability (~0.70) and shared environment (~0.21) estimates. The estimates did not change substantially when additional quantitative traits (height and weight) were added in a multivariate analysis. More generally for studies in genetics, the methodological innovation developed here implies that large (national) data collections can provide sufficient information on twin pairs to estimate genetic parameters, even without zygosity.     

Genetic and Environmental Causes of Tracking in Explosive Strength during Adolescence

Purpose: To determine whether the observed phenotypic stability in explosive strength during adolescence, as measured by inter-age correlations in vertical jump (VTJ), is mainly caused by genetic and/or environmental factors. Methods: Subjects are from the Leuven Longitudinal Twin Study (LLTS) (n = 105 pairs, equally divided over five zygosity groups). VTJ data were aligned on age at peak height velocity (APHV) to attenuate the temporal fluctuations in inter-age correlations caused by differences in timing of the adolescent growth spurt. Simplex models were fitted using structural equation modelling. Results: After aligning the data on APHV, the annual inter-age correlations show a clear simplex structure over a 4 year interval. The best fitting models included additive genetic and unique environmental sources of variation. Heritability estimates ranged between 60.8% (CI 37.7%–77.2%) and 87.3% (CI 74.2%–94.0%) for boys and between 76.5% (CI 56.7%–89.0%) and 88.6% (CI 77.8%–94.1%) for girls. Up to 56.4% and 62.8% of the total variation at the last measurement occasion is explained by additive genetic factors that already explained a significant amount of variation at previous measurement occasions in boys and girls respectively. It thus can be concluded that the observed stability of explosive strength during adolescence is mainly caused by a stable genetic influence in boys and girls. Conclusions: Additive genetic factors seem to be the main cause of the observed phenotypic stability in VTJ performance in boys and girls during adolescence.     

Heritability of Smoking Initiation and Nicotine Dependence

In contrast to other aspects of smoking behavior, little attention has been paid to the genetics of nicotine dependence. In this paper, three models (single liability dimension, independent liability dimension and combined model) have been applied to data on smoking initiation and nicotine dependence (n = 1572 Dutch twin pairs, mean age 30.5). A combined model best described the data. This model postulates a smoking initiation dimension and a nicotine dependence dimension, which are not independent. For both males and females, individual differences in smoking initiation were explained by genetic (44%), shared environmental (51%) and unique environmental (5%) influences. The nicotine dependence dimension was influenced only by genetic (75%) and unique environmental (25%) factors. The substantial impact of genetic factors on nicotine dependence emphasizes the need for further research to localize and identify specific genes and pathways involved in nicotine dependence.     

The Genetic Basis of Academic Achievement on the Queensland Core Skills Test and its Shared Genetic Variance with IQ

First, this study examined genetic and environmental sources of variation in performance on a standardised test of academic achievement, the Queensland Core Skills Test (QCST) (Queensland Studies Authority, 2003a). Second, it assessed the genetic correlation among the QCST score and Verbal and Performance IQ measures using the Multidimensional Aptitude Battery (MAB), [Jackson, D. N. (1984) Multidimensional Aptitude Battery manual. Port Huron, MI:Research Psychologist Press, Inc.]. Participants were 256 monozygotic twin pairs and 326 dizygotic twin pairs aged from 15 to 18 years (mean 17 years ± 0.4 [SD]) when achievement tested, and from 15 to 22 years (mean 16 years ± 0.4 [SD]) when IQ tested. Univariate analysis indicated a heritability for the QCST of 0.72. Adjustment to this estimate due to truncate selection (downward adjustment) and positive phenotypic assortative mating (upward adjustment) suggested a heritability of 0.76 The phenotypic (0.81) and genetic (0.91) correlations between the QCST and Verbal IQ (VIQ) were significantly stronger than the phenotypic (0.57) and genetic (0.64) correlations between the QCST and Performance IQ (PIQ). The findings suggest that individual variation in QCST performance is largely due to genetic factors and that common environmental effects may be substantially accounted for by phenotypic assortative mating. Covariance between academic achievement on the QCST and psychometric IQ (particularly VIQ) is to a large extent due to common genetic influences.