Twin Research and Human Genetics最新文献

The current study explored the impact of genetic relatedness differences (ΔH) and sample size on the performance of nonclassical ACE models, with a focus on same-sex and opposite-sex twin groups. The ACE model is a statistical model that posits that additive genetic factors (A), common environmental factors (C), and specific (or nonshared) environmental factors plus measurement error (E) account for individual differences in a phenotype. By extending Visscher's (2004) least squares paradigm and conducting simulations, we illustrated how genetic relatedness of same-sex twins (H_SS) influences the statistical power of additive genetic estimates (A), AIC-based model performance, and the frequency of negative estimates. We found that larger H_SS and increased sample sizes were positively associated with increased power to detect additive genetic components and improved model performance, and reduction of negative estimates. We also found that the common solution of fixing the common environment correlation for sex-limited effects to .95 caused slightly worse model performance under most circumstances. Further, negative estimates were shown to be possible and were not always indicative of a failed model, but rather, they sometimes pointed to low power or model misspecification. Researchers using kin pairs with ΔH less than .5 should carefully consider performance implications and conduct comprehensive power analyses. Our findings provide valuable insights and practical guidelines for those working with nontwin kin pairs or situations where zygosity is unavailable, as well as areas for future research.

Fetal sex contributes to the determination of obstetric outcome, as pregnancies carrying male babies seem to have an increased risk of maternal-fetal complications. Most studies have been conducted on singleton pregnancies, whereas less evidence is available for twins. A 10-year retrospective observational study was conducted on a cohort of 1180 women with twin pregnancy delivered at a single tertiary hospital. Clinical data on maternal characteristics, and obstetric and neonatal outcomes were collected, and the analysis was performed on monochorionic (MC) and dichorionic (DC) diamniotic twins separately. The group of DC twins included 837 cases, and those conceived by assisted reproductive technologies (ART) were more likely to have one or both female fetuses rather than males. The incidence of hypertensive disorders of pregnancy (HDP) was higher in same-sex pairs than in opposite-sex pairs. No differences were found regarding other obstetric and neonatal outcomes among the three sex-pairing groups. The MC twins group included 228 cases, and in female-carrying pregnancies a higher incidence of gestational diabetes (GDM) was observed compared to the male group. Furthermore, male pairs had significantly lower Apgar scores than females. Fetal sex seems to have a mild effect in twins compared to singleton pregnancies, suggesting a more complex set of factors contributing to pregnancy outcome in multiple pregnancies. However, we observed a higher incidence of HDP among same-sex DC pairs, a higher rate of GDM among MC female-female pairs, and a worse adaptation to extrauterine life among male-male pairs in MC twins.

A simple model by which Hardy-Weinberg proportions are attained in a single generation while maintaining gene frequencies is stated and illustrated. The title 'Quasi-random mating' is proposed. Confusion about the Hardy-Weinberg principle can be avoided only if there is clear separation between the basic deterministic model and factors influencing a population's structure. Eighty years passed before C. C. Li coined the term 'pseudo-random mating'. The lesson taught by Li has not been taken on board.

Schizophrenia (SZ) is a severe, complex, and common mental disorder with high heritability (80%), an adult age of onset, and high discordance (∼50%) in monozygotic twins (MZ). Extensive studies on familial and non-familial cases have implicated a number of segregating mutations and de novo changes in SZ that may include changes to the mitochondrial genome. Yet, no single universally causal variant has been identified, highlighting its extensive genetic heterogeneity. This report specifically focuses on the assessment of changes in the mitochondrial genome in a unique set of monozygotic twins discordant (MZD) for SZ using blood. Genomic DNA from six pairs of MZD twins and two sets of parents (N = 16) was hybridized to the Affymetrix Human SNP Array 6.0 to assess mitochondrial DNA copy number (mtDNA-CN). Whole genome sequencing (WGS) and quantitative polymerase chain reaction (qPCR) was performed for a subset of MZD pairs and their parents and was also used to derive mtDNA-CN estimates. The WGS data were further analyzed to generate heteroplasmy (HP) estimates. Our results show that mtDNA-CN estimates for within-pair and mother-child differences were smaller than comparisons involving unrelated individuals, as expected. MZD twins showed discordance in mtDNA-CN estimates and displayed concordance in directionality of differences for mtDNA-CN across all technologies. Further, qPCR performed better than Affymetrix in estimating mtDNA-CN based on relatedness. No reliable differences in HP were detected between MZD twins. The within-MZD differences in mtDNA-CN observed represent postzygotic somatic changes that may contribute to discordance of MZ twins for diseases, including SZ.

Establishing causal relationships in observational studies is an important step in research and policy decision making. The association between an exposure and an outcome can be confounded by multiple factors, often making it hard to draw causal conclusions. The co-twin control design (CTCD) is a powerful approach that allows for the investigation of causal effects while controlling for genetic and shared environmental confounding factors. This article introduces the CTCD and offers an overview of analysis methods for binary and continuous outcome and exposure variables. Tools for data simulation are provided, along with practical guidance and accompanying scripts for implementing the CTCD in R, SPSS, and Stata. While the CTCD offers valuable insights into causal inference, it depends on several assumptions that are important when interpreting CTCD results. By presenting a broad overview of the CTCD, this article aims to equip researchers with actionable recommendations and a comprehensive understanding of the design's strengths and limitations.

The aim of this study was to investigate the prevalence of anemia in twin pregnancies and the influence of anemia on maternal and neonatal outcomes. This retrospective study included twin pregnant women who delivered in a tertiary hospital in China from January 2018 to December 2018. Patients were divided by WHO criteria (hemoglobin <11.0 g/dL): the anemic and nonanemic groups. Patients with anemia were further classified as recovered or unrecovered subgroup after oral iron therapy. Maternal and neonatal outcomes in women carrying twins were compared using Student's t test and the chi-squared test or the Fisher exact test. Univariable and multivariable logistic regression models were used to determine the association of maternal and neonatal characteristics with anemia. Linear regression analysis was used to estimate mean birth weight and gestational week. The prevalence of anemia was 42.6% (182/427) in twin pregnancies. The anemic group had higher rates of low 1-minute Apgar score (4.4% vs. 1.8%, p = .028), perinatal death (1.9% vs. 0.2%, p = .012) and neonatal intensive care unit (NICU) admission (27.2% vs. 20.2%, p = .017; adjusted OR, 1.478; 95% CI [1.07, 2.044]). The recovered subgroup had lower NICU admission rate (13.5% vs. 30.3%, p = .006; OR, 0.388; 95% CI [0.186, 0.809]), higher gestational week and birth weight (β, 0.954 week; 95% CI [0.114, 1.794] and β, 171.01 g; 95% CI [9.894, 332.126] respectively). The prevalence of anemia in twin gestation is high. Anemia is associated with adverse neonatal outcomes, and correction of anemia significantly improved the pregnancy outcomes.

The 18th International Society for Twin Studies convention took place between June 15-17, 2023, in Budapest, Hungary. A selective sampling of highlights from the meeting are presented. This is followed by a brief overview of ongoing twin research at the University of Aberystwyth in Wales and some twin treasures in the National Library. Next, reviews of timely research that examine temperamental similarities and twin relations, the maximization of twin research designs, a rare ectopic twin pregnancy, and twins' academic self-concept formation are presented. The final section covers stories appearing in various media sources that are informative, enlightening, and interesting, namely a reunion of identical infant twins, the birth of identical-fraternal quadruplets, identical twin comedians, meeting an unrelated look-alike, and twins in the Tour de France.