Male Twin Pairs Research Articles

Multiparametric Analysis of Speaking Fundamental Frequency in Genetically Related Speakers Using Different Speech Materials: Some Forensic Implications.

To assess the speaker-discriminatory potential of a set of fundamental frequency estimates in intraidentical twin pair comparisons and cross-pair comparisons (i.e., among all speakers). A total of 20 Brazilian Portuguese speakers of the same dialect, namely 10 male identical twin pairs aged between 19 and 35, were recruited. The participants were recorded directly through professional microphones while taking part in a spontaneous dialogue over mobile phones. Acoustic measurements were performed in connected speech samples, and in lengthened vowels, at least 160ms long produced during spontaneous speech. f0 baseline, central tendency, and extreme values were found mostly discriminatory in intra-twin pair and cross-pair comparisons. These were also the estimates displaying the largest effect sizes. Overall, only three identical twins were found statistically different regarding their f0 patterns in connected speech, but not for lengthened vowel-based f0 metrics. Estimates of f0 variation and modulation were found the least discriminatory across speakers, which may signal the control of speaking style and dialect on dynamic patterns of f0. Concerning system performance, the base value of f0 (f0 baseline) was found the most reliable metric, displaying the lowest equal error rate (EER). The outcomes suggest that, although identical twins were very closely related regarding their f0 patterns, some pairs could still be differentiated acoustically, only in connected speech. Such findings reinforce the relevance of analyzing long-term f0 metrics for speaker comparison purposes, with particular consideration to f0 baseline. Furthermore, f0 differences across subjects were suggested as more expressive in connected speech than in lengthened vowels.

Concomitant Coronary Artery Disease in Identical Twins: Case Report and Systematic Literature Review.

Coronary artery disease (CAD) is multifactorial and strongly affected by genetic, epigenetic and environmental factors. Several studies have reported development of concomitant CAD in identical twins. We report a case in which a pair of Caucasian male monozygotic twins presented almost concomitantly with acute coronary syndrome (ACS) and had concordant coronary anatomy and identical site of occlusion. We performed a systematic literature review of PubMed, Web Of Science and Scopus databases from inception until 28 February 2023 of case reports/case series reporting the concomitant development of CAD in monozygotic twins. We found 25 eligible case reports with a total of 31 monozygotic twin pairs (including the case from our center) suffering from CAD and presenting (most of them simultaneously) with ACS (mean age of presentation: 45 ± 12 years, males: 81%). Coronary angiograms demonstrated lesion and anatomy concordance in 77% and 79% of the twin pairs, respectively. Screening for disease-related genetic mutations was performed in six twin pairs leading to the identification of five CAD-related genetic polymorphisms. This is the first systematic literature review of studies reporting identical twin pairs suffering from CAD. In summary, there is high concordance of coronary anatomy and clinical presentation between monozygotic twins. Future monozygotic twin studies-unbiased by age effects-can provide insights into CAD heritability being able to disentangle the traditional dyad of genetic and environmental factors and investigate the within-pair epigenetic drift.

Assisted Reproduction and Discussion of Rare Cases in Monozygotic Twinning.

Assisted reproductive technology is a crucial factor that increases the incidence of monozygotic twinning in humans. This article discusses the impact of various indicators in assisted reproductive technology studies on pregnancy outcomes, especially studies with a large number of clinical cases. Furthermore, three rare cases in multiples pregnancy are discussed: fetus papyraceous of a pair of male monozygotic twins in a set of triplets, two pairs of sesquizygotic twins with sex-discordance, and rare conjoined triplets.

Genetic and Environmental Factors Underlying Parallel Changes in Body Mass Index and Alcohol Consumption: A 36-Year Longitudinal Study of Adult Twins

Introduction: While the genetic and environmental underpinnings of body weight and alcohol use are fairly well-known, determinants of simultaneous changes in these traits are still poorly known. We sought to quantify the environmental and genetic components underlying parallel changes in weight and alcohol consumption and to investigate potential covariation between them. Methods: The analysis comprised 4,461 adult participants (58% women) from the Finnish Twin Cohort with four measures of alcohol consumption and body mass index (BMI) over a 36-year follow-up. Trajectories of each trait were described by growth factors, defined as intercepts (i.e., baseline) and slopes (i.e., change over follow-up), using latent growth curve modeling. Growth values were used for male (190 monozygotic pairs, 293 dizygotic pairs) and female (316 monozygotic pairs, 487 dizygotic pairs) same-sex complete twin pairs in multivariate twin modeling. The variances and covariances of growth factors were then decomposed into genetic and environmental components. Results: The baseline heritabilities were similar in men (BMI: h² = 79% [95% confidence interval: 74, 83]; alcohol consumption: h² = 49% [32, 67]) and women (h² = 77% [73, 81]; h² = 45% [29, 61]). Heritabilities of BMI change were similar in men (h² = 52% [42, 61]) and women (h² = 57% [50, 63]), but the heritability of change in alcohol consumption was significantly higher (p = 0.03) in men (h² = 45% [34, 54]) than in women (h² = 31% [22, 38]). Significant additive genetic correlations between BMI at baseline and change in alcohol consumption were observed in both men (rA = −0.17 [−0.29, −0.04]) and women (rA = −0.18 [−0.31, −0.06]). Non-shared environmental factors affecting changes in alcohol consumption and BMI were correlated in men (rE = 0.18 [0.06, 0.30]). Among women, non-shared environmental factors affecting baseline alcohol consumption and the change in BMI were inversely correlated (rE = −0.11 [−0.20, −0.01]). Conclusions: Based on genetic correlations, genetic variation underlying BMI may affect changes in alcohol consumption. Independent of genetic effects, change in BMI correlates with change in alcohol consumption in men, suggesting direct effects between them.

Epigenome-wide association study of physical activity and physiological parameters in discordant monozygotic twins

An epigenome-wide association study (EWAS) was performed on buccal cells from monozygotic-twins (MZ) reared together as children, but who live apart as adults. Cohorts of twin pairs were used to investigate associations between neighborhood walkability and objectively measured physical activity (PA) levels. Due to dramatic cellular epigenetic sex differences, male and female MZ twin pairs were analyzed separately to identify differential DNA methylation regions (DMRs). A priori comparisons were made on MZ twin pairs discordant on body mass index (BMI), PA levels, and neighborhood walkability. In addition to direct comparative analysis to identify specific DMRs, a weighted genome coexpression network analysis (WGCNA) was performed to identify DNA methylation sites associated with the physiological traits of interest. The pairs discordant in PA levels had epigenetic alterations that correlated with reduced metabolic parameters (i.e., BMI and waist circumference). The DNA methylation sites are associated with over fifty genes previously found to be specific to vigorous PA, metabolic risk factors, and sex. Combined observations demonstrate that behavioral factors, such as physical activity, appear to promote systemic epigenetic alterations that impact metabolic risk factors. The epigenetic DNA methylation sites and associated genes identified provide insight into PA impacts on metabolic parameters and the etiology of obesity.

Transcriptomic Differences Between Monozygotic Adolescent Twins Discordant For Metabolic Syndrome Following Weight Loss: A Case Study.

This case reports peripheral blood mononuclear cell (PBMC) transcriptomic changes in a pair of male monozygotic pediatric twins with metabolic syndrome (MetS) undertaking assisted weight loss. These 14-year-old boys presented with similar baseline biochemistry and body composition. After a 16-week weight-loss intervention, percent body weight loss was similar (Twin A 12%, and Twin B 13%). MetS resolved in Twin A but Twin B maintained elevated triglycerides after weight loss. Analysis of the PBMC transcriptome before and after weight loss revealed very different changes in gene expression including differences in the direction of expression of genes related to immune cell activation. 48.7% of genes that were downregulated in Twin A were upregulated in Twin B. This case highlights a novel approach to report the influence of chronic low-grade inflammation and metabolic dysfunction on the PBMC transcriptome. It explores whether expression of genes related to immune functions may underlie the differences in response to weight loss or whether transcriptomic alterations in immune cells may precede more traditional biomarkers of chronic pro-inflammation. These monozygotic twins present an example of divergence of phenotypic outcomes despite identical genetic background and similar treatment response.

Brazilian portuguese version of twin relationship questionnaire (TRQ-BR): Evidence of validity

Our aim was to adapt and validate a Brazilian Portuguese version of the Twin Relationship Questionnaire developed by Fortuna et al. (2010) and validated by H. Segal and Knafo-Noam (2019) in Israel. The respondents were 862 Brazilian mothers of twins ( N = 1724 twins) with mean age of 35 years (SD = 6.1). The majority of the sample lived in the Southeast (61.8%) or in the South (24.5%) of Brazil. We conducted a Multilevel Confirmatory Factor Analysis with the pair of twins as second level variable, and the five-factor structure (closeness, dependence, conflict, dominance, and rivalry) proposed by the original validation study of H. Segal and Knafo-Noam (2019) was confirmed. The final model retained 15 items out of 22 proposed in the original version of the questionnaire. Although the TRQ-BR has fewer items, the accuracy compared to the original questionnaire was maintained. Mixed Model Analysis (LMM) of TRQ scores were used to investigate twins’ relationships as a function of zygosity, age groups, and sex in order to provide evidence of convergent validity of the instrument. As expected, mothers perceived monozygotic twins (MZ) as more depedent than dizygotic twins (DZ). Furthermore, male twin pairs were considered more conflictive when compared to female twins. The present study showed that TRQ-BR is an adequate instrument for research purposes in the Brazilian population. It can also be useful for applied areas such as clinical and educational fields.

A descriptive analysis on type 2 diabetes in twins in China

Objective: To describe the distribution characteristics of type 2 diabetes in twins in Chinese National Twin Registry (CNTR), provide clues and evidence for revealing the influence of genetic and environmental factors for type 2 diabetes. Methods: Of all twins registered in the CNTR during 2010-2018, a total 18 855 twin pairs aged ≥30 years with complete registration information were included in the analysis. The random effect model was used to describe the population and area distribution characteristics and concordance of type 2 diabetes in twin pairs. Results: The mean age of the subjects was (42.8±10.2) years, the study subjects included 10 339 monozygotic (MZ) twin pairs and 8 516 dizygotic (DZ) twin pairs. The self-reported prevalence rate of type 2 diabetes was 2.2% in total population and there was no sighificant difference between MZ and DZ. Intra-twin pairs analysis showed that the concordance rate of type 2 diabetes was 38.2% in MZ twin pairs, and 16.0% in DZ twin pairs, the difference was statistically significant (P<0.001). The concordance rate of type 2 diabetes in MZ twin parts was higher than that in DZ twin pairs in both men and women, in different age groups and in different areas (P<0.05). Further stratified analysis showed that in northern China, only MZ twin pairs less than 60 years old were found to have a higher concordance rate of type 2 diabetes compared with DZ twin pairs (P<0.05). In southern China, the co-prevalence rate in male MZ twin pairs aged ≥60 years was still higher than that in DZ twin pairs (P<0.05). Conclusion: The twin pairs in this study had a lower self-reported prevalence of type 2 diabetes than the general population. The study results suggested that genetic factors play a role in type 2 diabetes prevalence in both men and women, in different age groups and in different areas, however, the effect might vary.

Heritability of tea drinking and its relationship with cigarette smoking in the Chinese male adult twins.

The aims of this study are to estimate the contributions of genetic factors to the variation of tea drinking and cigarette smoking, to examine the roles of genetic factors in their correlation and further to investigate underlying causation between them. We included 11 625 male twin pairs from the Chinese National Twin Registry (CNTR). Bivariate genetic modelling was fitted to explore the genetic influences on tea drinking, cigarette smoking and their correlation. Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) was further used to explore the causal relationship between them. We found that genetic factors explained 17% and 23% of the variation in tea drinking and cigarette smoking, respectively. A low phenotypic association between them was reported (rph = 0.21, 95% confidence interval [CI]: [0.19, 0.24]), which was partly attributed to common genetic factors (rA = 0.45, 95% CI [0.19, 1.00]). In the ICE FALCON analysis with current smoking as the exposure, tea drinking was associated with his own (βself = 0.39, 95% CI [0.23, 0.55]) and his co-twin's smoking status (βco-twin = 0.25, 95% CI [0.10, 0.41]). Their association attenuated with borderline significance conditioning on his own smoking status (p = 0.045), indicating a suggestive causal effect of smoking status on tea drinking. On the contrary, when we used tea drinking as the predictor, we found familial confounding between them only. In conclusion, both tea drinking and cigarette smoking were influenced by genetic factors, and their correlation was partly explained by common genetic factors. In addition, our finding suggests that familial confounders account for the relationship between tea drinking and cigarette smoking. And current smoking might have a causal effect on weekly tea drinking, but not vice versa.

Concordance of keratoconus in monozygotic twins before and after combined corneal crosslinking/photorefractive keratectomy (Athens Protocol) using Scheimpflug and OCT tomography.

To describe the concordance of keratoconus (KC) expression in 2 pairs of monozygotic twins before and after a combined corneal crosslinking (CXL)/photorefractive keratectomy (PRK) procedure. Private ambulatory eye surgery unit. Retrospective interventional twin study. Two pairs of male monozygotic twins with KC were studied retrospectively. Improvement of flattest (K1) and steepest (K2) keratometry, index of height decentration (IHD), and corneal thickness at the thinnest point and corneal epithelial thickness measured by anterior segment optical coherence tomography and Scheimpflug tomography was compared between respective eyes of monozygotic twin siblings 1 to 5 years after the application of combined CXL and topography-guided PRK of part of the refractive error (the Athens Protocol). Significant improvement was noted in all the keratometric indices of all 8 eyes after the combined CXL/PRK procedure. The difference in K1, K2, IHD, corneal thickness at the thinnest point, and corneal epithelial thickness percentage improvement between the right eyes of each pair of twins was statistically significant 1 year and 5 years postoperatively (P < .05). Statistically significant discordance in the aforementioned parameters percentage improvement was similarly observed between the left eyes of each pair of twins (P < .05). Although a genetic predisposition in KC is well documented, the discordance in keratometric indices improvement after a CXL/PRK procedure between respective eyes of monozygotic twins suggests that environmental influences may contribute to the disease expression as well. Variable degree of synergy in a combined CXL/PRK procedure may also explain the aforementioned discordant improvement.

Genetic and Environmental Influences on Perceived Social Support: Differences by Sex and Relationship.

Previous research has shown that self-reports of the amount of social support are heritable. Using the Kessler perceived social support (KPSS) measure, we explored sex differences in the genetic and environmental contributions to individual differences. We did this separately for subscales that captured the perceived support from different members of the network (spouse, twin, children, parents, relatives, friends and confidant). Our sample comprised 7059 male, female and opposite-sex twin pairs aged 18-95 years from the Australian Twin Registry. We found tentative support for different genetic mechanisms in males and females for support from friends and the average KPSS score of all subscales, but otherwise, there are no sex differences. For each subscale alone, the additive genetic (A) and unique environment (E) effects were significant. By contrast, the covariation among the subscales was explained - in roughly equal parts - by A, E and the common environment, with effects of different support constellations plausibly accounting for the latter. A single genetic and common environment factor accounted for between half and three-quarters of the variance across the subscales in both males and females, suggesting little heterogeneity in the genetic and environmental etiology of the different support sources.

Genetically informative analysis of the association between intimate relationship adjustment and health.

Prior research has found a positive association between the quality or adjustment of an individual's intimate relationship, such as marriage, and their physical health. However, it is possible that this association may be due, at least in part, to confounding variables (i.e., variables that are causally associated both with relationship adjustment and health and could account for their covariation), including genetically influenced confounds. This study was conducted using a genetically informative sample of twins to examine the association between intimate relationship adjustment and self-rated health, accounting for unmeasured genetic and environmental confounds. A Swedish sample of 539 monozygotic and dizygotic twins (321 male twin pairs and 218 female twin pairs) and their spouse or long-term partner completed self-report measures of relationship adjustment and health. Relationship adjustment was positively associated with self-rated health in male and female twins. For male twins, nonshared environmental influences largely accounted for the association between relationship adjustment and health; for female twins, this association was generally explained by shared and nonshared environmental influences. For male twins, results obtained from partners' reports of relationship adjustment were largely consistent with those obtained from twins' reports. Results suggest that the association between relationship adjustment and self-rated health remains after accounting for shared genetic influences, and that nonshared environmental influences, such as partners' characteristics, account for the association between relationship adjustment and self-rated health in men. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Whole-Genome Differentially Hydroxymethylated DNA Regions among Twins Discordant for Cardiovascular Death.

Epigenetics is a mechanism underlying cardiovascular disease. It is unknown whether DNA hydroxymethylation is prospectively associated with the risk for cardiovascular death independent of germline and common environment. Male twin pairs middle-aged in 1969–1973 and discordant for cardiovascular death through December 31, 2014, were included. Hydroxymethylation was quantified in buffy coat DNA collected in 1986–1987. The 1893 differentially hydroxymethylated regions (DhMRs) were identified after controlling for blood leukocyte subtypes and age among 12 monozygotic (MZ) pairs (Benjamini–Hochberg False Discovery Rate < 0.01), of which the 102 DhMRs were confirmed with directionally consistent log2-fold changes and p < 0.01 among additional 7 MZ pairs. These signature 102 DhMRs, independent of the germline, were located on all chromosomes except for chromosome 21 and the Y chromosome, mainly within/overlapped with intergenic regions and introns, and predominantly hyper-hydroxymethylated. A binary linear classifier predicting cardiovascular death among 19 dizygotic pairs was identified and equivalent to that generated from MZ via the 2D transformation. Computational bioinformatics discovered pathways, phenotypes, and DNA motifs for these DhMRs or their subtypes, suggesting that hydroxymethylation was a pathophysiological mechanism underlying cardiovascular death that might be influenced by genetic factors and warranted further investigations of mechanisms of these signature regions in vivo and in vitro.

Investigation of Skeletal Muscle Mitochondrial Function Following an Ultramarathon: A Case Study in Monozygotic Twins

The primary objective of this case study was to investigate the changes in skeletal muscle mitochondria that occur in response to a 100-km ultramarathon in monozygotic twins. Secondarily, we sought to determine if periodically consuming a low-carbohydrate, high-fat diet (LCHFD) during training would affect these changes. To accomplish these objectives, one pair of male monozygotic twins ran 100 km side-by-side on treadmills. During 8 weeks of training leading up to this event, twin 1 (T1) and twin 2 (T2) consumed a calorie and macronutrient-matched, high-carbohydrate diet, with the exception of 2 consecutive days per week for the final 4 weeks where T2 consumed a calorie and protein-matched LCHFD. Training load was matched between the subjects, most of which they completed together. The subjects were extremely well-matched in VO2 max (61.2 and 60.3 ml/kg/min), BMI (20.4 and 20.6 kg/m2), and body mass (62 and 61.9 kg). During the 100-km run, food and fluid intake were matched, as well as the pace of the run. The run took 16 hours and 3 minutes to complete. Blood draws and muscle biopsies from the vastus lateralis were collected 4 weeks prior to the run, as well as 4- and 52-hours post-run. During the last 4 weeks of training, T2 lost an average of ~1 kg of body weight (BW) over the two days of LCHFD each week (comparing BW of 4 consecutive Mondays to Wednesdays, p=0.02), which was regained two days after reintroduction of carbohydrate, consistent with fluctuating glycogen levels. Though T2 trained with periodically low glycogen levels, respiratory-exchange ratio was no different from T1 throughout the 100-km run. Four hours post-run, state 3, uncoupled, and fatty acid-supported mitochondrial respiration were reduced in T1 by 22.3%, 34.1% and 25.7%, respectively, and by 28.4%, 49.4% and 39.9% in T2, which was associated with a decrease of 15-20% in citrate synthase (CS) activity. Both twins exhibited decreases in mitochondrial complex proteins, though this was more marked in T2. Blood CPK, CRP, and AST levels were also elevated post-run. Possibly the most novel finding from this study was that 52 hours post-run, respiratory capacity, mitochondrial proteins, CS activity and blood markers showed signs of rapid recovery. It is currently unclear by what mechanism mitochondrial respiration and content was reduced 4 hours post-run, or how it recovered in 2 days. Interestingly, maximal mitochondrial ROS production (glutamate, malate and succinate-supported) was decreased post-run at both timepoints but was increased compared to baseline with the addition of ADP (12.5 μM – 100 μM). This suggests that the mitochondria were less sensitive to ADP-induced reductions in ROS. Neither diet resulted in better preservation of mitochondrial function 4-hours post-run, though T2 showed some signs of supercompensation 52 hours-post run. This study is valuable because it provides evidence of an acute reduction in mitochondrial content and function following ultra-endurance activity, followed by rapid recovery. This study was approved by the Brigham Young University Institutional Review Board and conformed to the principles of human experimentation set by the Declaration of Helsinki.

Erectile Dysfunction in Young Men: Testosterone, Androgenic Polymorphisms, and Comorbidity With Premature Ejaculation Symptoms

BackgroundThe association between erectile dysfunction (ED), free testosterone (T), and androgenic genetic polymorphisms is still unclear. As most studies in the field have focused on older (>40 y.o.) men, data from young men is scarce. In addition, the clinically observed comorbidity between ED and premature ejaculation (PE) has not been explained. AimThe aim of the present study was 3-fold: to assess in a sample of young men (1) the association between ED and T; (2) the role of androgenic genetic polymorphisms in the aforementioned association; and (3) comorbidity between ED and PE symptoms. MethodsStatistical analyses were performed on a population-based sample of 2,302 Finnish men, (Mage = 26.8 years). Hormone samples were available from 317 men, and genotype information was available from a minimum of 1,144 men depending on genetic locus. For twin analyses, the sample contained 533 male individuals from opposite-sex fraternal twin pairs, 491 identical male individuals (110 complete pairs), 493 male individuals from male fraternal twin pairs (92 complete pairs), and 658 siblings of twins. OutcomesThe main outcome measure includes association between levels of salivary T and ED, main effects of the androgen-related genetic polymorphisms on ED scores. Bivariate twin models of PE and ED were fitted to elucidate possible shared etiology. ResultsWe found no significant association between T levels and ED and no significant main effects of the androgenic genetic polymorphisms on ED. We found no evidence suggesting that any of the genetic polymorphisms would moderate the association between T and ED symptoms. We found shared unique environmental influences between PE and ED (rE = .28). Clinical TranslationObtained data suggest that ED has T-independent causes and that any comorbidity between PE and ED is not explained by a set of genes affecting both phenotypes. Strengths & LimitationsFirst, the sample size for both parts of the study was relatively small, which may make some statistical analyses underpowered. Furthermore, as the sample was a population-based sample of relatively young men, the number of clinically relevant ED cases was low. Second, some concerns about T derived from saliva exist because saliva sampling comes with increased risks of error particularly because saliva samples are more vulnerable to contamination. ConclusionWe found no significant association between free T levels, androgenic genetic polymorphisms, and ED in the younger age cohort. Twin analysis suggested a common nonshared environmental component in PE and ED.Zhuravleva1 ZD, Johansson A, Jern P. Erectile Dysfunction in Young Men: Testosterone, Androgenic Polymorphisms, and Comorbidity With Premature Ejaculation Symptoms. J Sex Med 2021;18:265–274.

The Moderating Influence of School Achievement on Intelligence in Young Adulthood.

Education has been suggested to be possibly the most consistent, robust, and durable method available for raising intelligence, but little is known about the genetic and environmental interplay underlying this association. Therefore, we investigated how school achievement, as measured by grade point average in lower secondary school at 15years of age, moderated intelligence variation in young adulthood. The sample consisted of all Danish male twin pairs who had left lower secondary school since 2002 and appeared, typically at age 18, before a draft board through 2015 (N = 2660). Shared environmental variance unique to intelligence (10% of total variance) was found to be greater among individuals with poor school achievement. However, school achievement did not moderate the genetic influences or the non-shared environmental influences on intelligence. We discuss the implications of this in light of the constraints imposed by the statistical models we used.

Twins Living Apart: Behavioral Insights/Twin Study Reviews: Managing Monochorionic-Diamniotic Twin Pregnancies; Paternity Testing in Multiple Pregnancies; Twin Research on Resilience; Trisomies in Twin Pregnancies/Human Interest: Reunited Brazilian Twins; Website for Twins with Disabled Co-Twins; Twins Separated in Secret of the Nile Series; Mengele: Unmasking the Angel of Death; Twins Helping Others.

A brief review of research findings regarding twins living apart is presented. This review is followed by a look into the lives of a pair of monozygotic male twins who have lived in different continents for many years, but who stay closely connected. The reasons behind their decision and its impact on their behavioral resemblance and social relationship quality are examined. The next section summarizes recent studies that address the management of monochorionic-diamniotic twin pregnancies, paternity testing in multiple pregnancies, trisomies in twin pregnancies and the roots of resilience. The final portion of this article presents human-interest stories involving reunited Brazilian twins, a new resource for twins with disabled co-twins, twins separated in the Secret of the Nile television series, a new book about Dr Josef Mengele and his horrific twin experiments conducted at the Auschwitz-Birkenau concentration camp, and a pair of twins dedicated to helping others.

Genetic and Environmental Influences on Blood Pressure and Body Mass Index in the National Academy of Sciences-National Research Council World War II Veteran Twin Registry.

Blood pressure (BP) and obesity phenotypes may covary due to shared genetic or environmental factors or both. Furthermore, it is possible that the heritability of BP differs according to obesity status-a form of G×E interaction. This hypothesis has never been tested in White twins. The present study included 15 924 White male twin pairs aged between 15 and 33 years from the National Academy of Sciences-National Research Council World War II Veteran Twin Registry. Systolic and diastolic BPs, as well as height and weight, were measured at the induction physical examination. Body mass index (BMI) was used as the index of general obesity. Quantitative genetic modeling was performed using Mx software. Univariate analysis showed that narrow sense heritabilities (95% CI) for systolic BP, diastolic BP, height, and BMI were 0.401 (0.381-0.420), 0.297 (0.280-0.320), 0.866 (0.836-0.897), and 0.639 (0.614-0.664), respectively. Positive phenotypic correlations of BMI with systolic BP (r=0.13) and diastolic BP (r=0.08) were largely due to genetic factors (70% and 86%, respectively). The gene-BMI interaction analysis did not show any support for a modifying effect of BMI on genetic and environmental influences of systolic BP and diastolic BP. Our results suggest that correlations between BP and BMI are mainly explained by common genes influencing both. Higher BMI levels have no influence on the penetrance of genetic vulnerability to elevated BP. These conclusions may prove valuable for gene-finding studies.

The Effects of Education on Mortality: Evidence From Linked U.S. Census and Administrative Mortality Data.

Does education change people's lives in a way that delays mortality? Or is education primarily a proxy for unobserved endowments that promote longevity? Most scholars conclude that the former is true, but recent evidence based on Danish twin data calls this conclusion into question. Unfortunately, these potentially field-changing findings-that obtaining additional schooling has no independent effect on survival net of other hard-to-observe characteristics-have not yet been subject to replication outside Scandinavia. In this article, we produce the first U.S.-based estimates of the effects of education on mortality using a representative panel of male twin pairs drawn from linked complete-count census and death records. For comparison purposes, and to shed additional light on the roles that neighborhood, family, and genetic factors play in confounding associations between education and mortality, we also produce parallel estimates of the education-mortality relationship using data on (1) unrelated males who lived in different neighborhoods during childhood, (2) unrelated males who shared the same neighborhood growing up, and (3) non-twin siblings who shared the same family environment but whose genetic endowments vary to a greater degree. We find robust associations between education and mortality across all four samples, although estimates are modestly attenuated among twins and non-twin siblings. These findings-coupled with several robustness checks and sensitivity analyses-support a causal interpretation of the association between education and mortality for cohorts of boys born in the United States in the first part of the twentieth century.

Twin Data: The Lives That Drive the Findings/Twin Research Reviews: Twin Concordance for Kleine-Levin Syndrome; Twin Study of Political Discussion; Twin Relationship Quality and Urinary Cortisol Level; Twin Research Guide/In the News: Twins' Same Day Deliveries; Death of a Twin Holocaust Survivor; Identical Vindman Twins; Twin Festival in France; Tiniest Twins.

Twin data and the results generated by research are driven by the behavioral and physical attributes of twin participants. However, many investigators working with twin data have limited personal contact with actual twin-pairs. This situation may be limiting with respect to interpretation of results and formulation of new hypotheses. In an attempt to rectify this issue, key aspects of the interconnected lives of co-twins in three monozygotic male twin-pairs are presented. The section that follows includes a review of twin research on Kleine-Levin syndrome, political discussion, twin relationship quality and urinary cortisol level, and guidelines for determining sample sizes. The final part of this report presents twin-related news items relating to twins' same day deliveries, death of a twin Holocaust survivor, the Vindman twins, a twin festival in France and the tiniest twins on record.