Recent research has provided strong support for the existence of a familial risk for suicide, and efforts have been made to separate genetic from enviromental risk factors. Twin studies have played a major role in the identification of genetic factors, and the results indicate that the concordance rate for suicide is higher in identical than in fraternal twins (Baldessarini & Hennen, 2004). Moreover, Segal and Roy (1995) reported a significantly higher frequency of nonfatal suicidal attempts by monozygotic (MZ) than by dyzygotic (DZ) twins whose co-twins had committed suicide. However, doubts remain as to whether the increased risk of suicide in MZ twins is a response to the intense grief over the loss of a close relative, or whether a common genotype is associated with suicidal behavior. Sudden loss, which may carry a stigma in the case of a suicide, has been linked to increased persistent emotional stress and physiological changes (Epstein, 1993; Martin & Dean, 1993). A number of researchers have reported greater suicidal ideation among bereaved MZ twins as compared to DZ twins, suggesting that a loss due to suicide may increase the risk of suicidal behavior in the surviving co-twin (Segal & Bouchard, 1993; Segal & Roy, 1995; Segal et al., 1995). The aim of the present article is to address the issue of the intense grief experienced by twins after the co-twin suicide.

Fetal movements and fetal heart rate (FHR) are well-established markers of fetal well-being and maturation of the fetal central nervous system. The purpose of this paper is to review and discuss the available knowledge on fetal movements and heart rate patterns in twin pregnancies. There is some evidence for an association or similarity in fetal movement incidences or FHR patterns between both members of twin pairs. However, the temporal occurrence of these patterns seems to be for the most part asynchronous, especially when stricter criteria are used to define synchrony. The available data suggest that fetal behavior is largely independent of sex combination, fetal position, and presentation. Conversely, chorionicity appears to have some influence on fetal behavior, mainly before 30 weeks of gestation. There is preliminary evidence for the continuity of inter-individual differences in fetal activity and FHR patterns over pregnancy. Comparisons between studies are limited by large methodological differences and absence of uniform concepts and definitions. Future studies with high methodological quality are needed to provide a more comprehensive knowledge of normal fetal behavior in twin pregnancy.

This study was conducted to determine the incidence of cerebral injury as detected by postnatal brain scan in monochorionic twins with selective intrauterine growth restriction. Having excluded cases complicated with twin-to-twin transfusion syndrome and one co-twin suffering intrauterine fetal death, a total of 73 monochorionic twin pregnancies divided into absence (group I, n = 46) or presence (group II, n = 27) of selective intrauterine growth restriction. Mild cerebral injury was defined as presenting one of the following abnormal cranial scan findings: intraventricular hemorrhage grade I, grade II, lenticulostiate vasculopathy and/or subependymal pseudocysts, while severe cerebral injury was defined as presenting intraventricular hemorrhage grade III, grade IV, cystic periventricular leukomalacia (PVL) grade II or higher, porencephalic cysts, and/or ventricular dilatation. The incidence of mild cerebral injury was not significantly different between these two groups (eight cases in group I and six cases in group II). Except for one case that later developed a seizure, the majority (13 out of 14) of cases with minor brain scan anomalies were only transient, without significant clinical impact. There was only one case diagnosed with a major brain scan anomaly (periventricular leukomalacia) in group II. One severe brain injury and three neonatal deaths all belonged to group II with abnormal umbilical artery Doppler in the growth restricted twin. In conclusion, the incidence of severe cerebral injury in monochorionic twin pregnancies with selective intrauterine growth restriction was low, at 3.7%.

Pregnancy outcome and characteristics of women who conceive following subfertility treatment remains a subject of great interest. We analyzed these variables among 199 women who delivered a registerable twin birth compared with 1773 women who delivered a naturally conceived twin birth in a population-based obstetric cohort drawn from around Oxford, England. Treatment was restricted to conceptions involving simple ovulation induction only. Treated mothers were of significantly higher social class and older, more likely to deliver girls and to be delivered by cesarean section, and significantly less likely to be smokers at the time of antenatal booking and to have delivered previous pregnancies. Pregnancy outcome was similar between the two groups for most measures, with the exception of birthweight which was lower in treated twins, though not significantly so. Overall the results are reassuring with respect to outcome in twin pregnancies following simple ovulation induction.

Background and objective: Intrauterine growth restriction (IUGR) may be associated with significantly higher aortic intima–media thickening (aIMT) values. It is unknown if fetal aIMT is associated with glomerulosclerosis and amniotic albuminuria in utero. Design, setting, participants, and measurements: Fetal abdominal aIMT and amniotic albumin/creatinine ratio (ACR) were measured in 126 individual twin fetuses, recruited by the Obstetrics and Gynaecology Clinics of the University of Padua (Italy) Medical Center. The IUGR twin fetuses were classified into two groups: Group A were those fetuses whose estimated fetal weight (EFW) was <10th percentile with pulsatility index >2 SD and Group B were those fetuses whose EFW was <10th percentile and had no velocimetry abnormalities. Results: The median fetal aIMT was significantly different in the three groups (Group A = 0.9 mm; Group B = 0.7 mm; and appropriate for gestational age (AGA) = 0.5 mm; p < .0001). It was significantly higher in Group A than in the AGA group (p < .0001) and than in the Group B fetuses (p = .003), respectively. In addition, ACR was different in the three groups (Group A = 183,500 mg/g; Group B = 6,4720 mg/g; and AGA = 8,2750 mg/g; p = .0002). It was significantly higher in Group A than in the AGA group (p = .03) and than in Group B (p = .02), respectively. Conclusions: Growth-restricted twin fetuses with velocimetry abnormalities present are associated with aIMT and higher ACR levels in amniotic fluid, which could be possible markers in utero of preclinical atherosclerosis, and early glomerulosclerosis.

The University of São Paulo Twin Panel (Painel USP de Gêmeos), based at the Institute of Psychology of the University of São Paulo, started formally in 2017. Our registry is new, but in only two years of formal existence, it comprises a volunteer sample of 4826 registered individuals (98% twins and 2% higher-order multiples), recruited at the University of São Paulo and by social media campaigns. Our main aim is to conduct and promote research with twins on psychological processes and behavior. The University of São Paulo is the largest higher education and research institution in South America, and the Painel USP de Gêmeos has great potential for fostering research on twin-related issues from a psychological perspective in Brazil and South America.

To date, several studies have investigated the intergenerational effect of preterm and small-for-gestational-age (SGA) births. However, most studies excluded both twin mothers and twin offspring from the analyses. Thus, the objective of this study was to investigate the intergenerational effect of preterm birth and SGA births among twins and singletons. A prospective population-based register study of mother–firstborn offspring pairs recorded in the Swedish Medical Birth Register was performed. The study included 4,073 twins and 264,794 singletons born from 1973–1983 and their firstborns born from 1986–2009. Preterm birth was defined as birth at <37 weeks of gestation, and SGA as birth weight <2 standard deviations of the Swedish standard. Logistic regressions were performed to estimate the intergenerational effect of each birth characteristic. Adjustments were made for maternal grandmothers’ and mothers’ socio-demographic factors, in addition to maternal birth characteristics. Among mothers born as singletons, being born preterm was associated with an increased risk of delivering a preterm child (adjusted odds ratio (OR) 1.39, 95% Confidence Interval (CI) = 1.29–1.50), while being born SGA increased the likelihood of having an SGA child (adjusted OR 3.04, 95% CI = 2.80–3.30) as well as a preterm child (adjusted OR 1.30, 95% CI = 1.20–1.40). In twin mothers, the corresponding ORs tended to be lower, and the only statistically significant association was between an SGA mother and an SGA child (adjusted OR 2.15, 95% CI = 1.40–3.31). A statistically significant interaction between twinning and mother's size for gestational age was identified in a multivariate linear regression analysis, indicating that singleton mothers born SGA were associated with a lower birth weight compared with mothers not born SGA. Preterm birth and SGA appear to be transferred from one generation to the next, although not always reaching statistical significance. These effects seem to be less evident in mothers born as twins compared with those born as singletons.

Advances in perinatal technology that improved survival may have also resulted in prolonged death from the neonatal to the postneonatal period for some infants. The objectives of this study were to determine if the medical advances that occurred in the 1990s benefited infants of multiple births more than their singleton counterparts, and if these changes prevented or postponed mortality for the smallest and most immature infants. The study population included live births of 22 to 43 weeks' gestation from the 1989–1991 and 1999–2001 US Birth Cohort Linked Birth/Infant Death Data Sets. Odds ratios were calculated to evaluate the change in risk by plurality, gestation, and to compare the change to that for singletons. Neonatal and infant mortality rates declined for all pluralities; postneonatal mortality increased for births at less than 26 weeks, but declined at later gestations. In general, the risk of death for twins and triplets compared to singletons decreased, and the improvement in survival was greater for multiples during the early neonatal period and overall. Infant mortality rates improved by 28% for singletons, 32% for twins and triplets during the 1990s, although for the most premature infants, some deaths were postponed from the early to the late neonatal period.

Hydroxysteroid (17-beta)dehydrogenase 1(HSD17B1) plays a central role in sex steroid hormone metabolism. HSD17B1 polymorphic variants may contribute to cancer susceptibility. Numerous investigations have been conducted to assess the association between HSD17B1 Ser312Gly polymorphism and cancer risk in multiple ethnicities, yet these have produced inconsistent results. We therefore performed this comprehensive meta-analysis to attempt to provide a quality assessment of the association of interest. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to evaluate the strength of associations. After a systematic literature search of several major public databases, 20 studies involving 29,460 cases and 36,687 controls were included in this meta-analysis. No significant association was found between HSD17B1 Ser312Gly polymorphism and cancer risk. However, Ser312Gly polymorphism showed a significantly decreased risk for Caucasians (there were 44,284 Caucasians for analysis, comprising 19,889 cases and 24,395 controls) in the subgroup analysis by ethnicity (dominant: OR = 0.958, 95% CI = 0.919–0.998; and allele comparing: OR = 0.973, 95% CI = 0.947–0.999). And there was the same trend towards risk in the population-based (PB) controls (homozygous: OR = 0.951, 95% CI = 0.908–0.997 and allele comparing: OR = 0.976, 95% CI = 0.954–0.999), but not among Asians or hospital-based (HB) controls. In addition, no association was observed in the stratified analysis for breast cancer studies by source of control, ethnicity and quality score. These findings suggested that the HSD17B1 Ser312Gly polymorphism might confer genetic cancer susceptibility in an ethnic-dependent manner, especially among Caucasians. Well-designed, large-scale studies are warranted to validate these findings.

Obesity is a substantial health problem in the United States, and is associated with many chronic diseases. Previous studies have linked poor dietary habits to obesity. This cross-sectional study aimed to identify the association between body mass index (BMI) and fast-food consumption among 669 same-sex adult twin pairs residing in the Puget Sound region around Seattle, Washington. We calculated twin-pair correlations for BMI and fast-food consumption. We next regressed BMI on fast-food consumption using generalized estimating equations (GEE), and finally estimated the within-pair difference in BMI associated with a difference in fast-food consumption, which controls for all potential genetic and environment characteristics shared between twins within a pair. Twin-pair correlations for fast-food consumption were similar for identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins, but were substantially higher in MZ than DZ twins for BMI. In the unadjusted GEE model, greater fast-food consumption was associated with larger BMI. For twin pairs overall, and for MZ twins, there was no association between within-pair differences in fast-food consumption and BMI in any model. In contrast, there was a significant association between within-pair differences in fast-food consumption and BMI among DZ twins, suggesting that genetic factors play a role in the observed association. Thus, although variance in fast-food consumption itself is largely driven by environmental factors, the overall association between this specific eating behavior and BMI is largely due to genetic factors.

Traditional theories of political participation have emphasized its social and normative components; however, recent evidence suggests that political participation has a strong additive genetic component. Accordingly, it is necessary to reevaluate the traditional empirical findings and begin to integrate the two approaches. To do so, a variety of analyses were conducted that explore the modes of genetic and environmental transmission. I find that the empirical estimates of the relationships between the phenotypic level traits are highly consistent with what has been found in the traditional literature, the vast majority of the variance in political participation that is accounted for by the predictor variables is being accounted for at the genetic level, and not at the environmental level. Thus, the current findings suggest that the empirical results found in prior studies are quite likely very accurate. However, the interpretation of those empirical findings, as well as the subsequent theoretical implications, require serious revision.

Neuroticism, a ‘Big Five’ personality trait, has been associated with sub-clinical traits of both autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). The objective of the current study was to examine whether causal overlap between ASD and ADHD traits can be accounted for by genetic and environmental risk factors that are shared with neuroticism. We performed twin-based structural equation modeling using self-report data from 12 items of the Neo Five-Factor Inventory Neuroticism domain, 11 Social Responsiveness Scale items, and 12 Adult ADHD Self-Report Scale items obtained from 3,170 young adult Australian individual twins (1,081 complete pairs). Univariate analysis for neuroticism, ASD, and ADHD traits suggested that the most parsimonious models were those with additive genetic and unique environmental components, without sex limitation effects. Heritability of neuroticism, ASD, and ADHD traits, as measured by these methods, was moderate (between 40% and 45% for each respective trait). In a trivariate model, we observed moderate phenotypic (between 0.45 and 0.62), genetic (between 0.56 and 0.71), and unique environmental correlations (between 0.37and 0.55) among neuroticism, ASD, and ADHD traits, with the highest value for the shared genetic influence between neuroticism and self-reported ASD traits (r g = 0.71). Together, our results suggest that in young adults, genetic, and unique environmental risk factors indexed by neuroticism overlap with those that are shared by ASD and ADHD.

This article profiles the historical twin databases of the secondary education school attached to the Faculty of Education at the University of Tokyo. The school was established in 1948. Every year, about 50 pairs of twins of all sex and zygosity combinations and aged 11 to 12 years take an examination, and about 10 to 20 pairs are admitted based on the results. Three independent datasets exist: one for applicants (11–12 years), one for students (12–18 years), and one for graduates (18–72 years). These three historical databases and research perspectives are introduced herein.

In the 19th century, a series of international statistical congresses began that were important for population studies, including twin research. The introduction of common rules for the national demographic registers enabled scientists to contribute to the genesis of statistical research. The congress in St. Petersburg in 1872, in particular, focused on the movements of the population, and how they should be registered. Among the facts to be recorded were in multiple births, the sex and number of children born alive or still-born, whether legitimate or illegitimate, and the age of the mother at the date of the births. During the history of twin research, Hellin's law has played a central role because it is an approximately correct association between the rates of multiple maternities. It has been mathematically proven that Hellin's law does not hold as a general rule. Analyses show divergences from the law that are difficult to explain and/or eliminate. Varying improvements of this law have been proposed. The majority of all studies of Hellin's law are based on empirical rates of multiple maternities, ignoring random errors. Such studies can never confirm the law, but only identify errors with respect to Hellin's law that are too large to be characterized as random. It is of particular interest to note and explain why the rates of higher multiple maternities are sometimes too high or too low when Hellin's law is used as a benchmark. Studies have shown that there were investigators before Hellin who have contributed substantially to Hellin's law. In this article, we re-examine some old data sets and contributions in which Hellin's law has been evaluated and also analyze recent data.

Asthma and hay fever are likely to share hundreds if not thousands of genetic risk variants. Despite this, the extent to which the power to identify shared risk variants could be improved by considering information from both diseases when designing or analyzing genetic studies has not been studied in detail. Simulations were performed to quantify the power to detect an association between case-control status and a bi-allelic risk variant shared between asthma and hay fever across a range of disease and genetic models, as well as different ascertainment and analytical strategies. For a fixed sample size, when designing a new genome-wide association study (GWAS), selecting for genotyping cases with both asthma and hay fever (A+H+), and controls with neither disease (A-H-) was the study design that provided the greatest power to identify a shared risk variant. On the other hand, when analyzing an existing GWAS, power was greatest across a wide range of scenarios, when cases were defined as individuals who suffered from either disease (A+ or H+) and controls as those who suffered from neither (A-H-). Bivariate analysis of asthma and hay fever provided comparable but slightly decreased power. In conclusion, new GWAS can be designed and existing GWAS reanalyzed more efficiently to identify risk variants for allergic disease by using ascertainment or analytical strategies that consider both asthma and hay fever information.

Genetic and environmental influences on age at menarche (AAM) have rarely been examined in Asian females. This study aimed to investigate the heritability of AAM in South Korean female twins. The AAM data from 1370 female twins (933 monozygotic [MZ] twins, 294 dizygotic [DZ] twins and 160 female members of opposite-sex DZ twins) born between 1988 and 2001 were analyzed. The age of the sample at the time of the assessment ranged from 16 to 28 years with a mean of 19.3 (SD = 2.2) years. The mean AAM in the total sample was 12.49 (SD = 1.41) years. Although the mean AAM decreased with increasing birth years, it levelled off in birth years 2000–2001. Maximum likelihood MZ and DZ twin correlations were 0.72 [95% CI (0.67, 0.76)] and 0.35 [95% CI (0.19, 0.50)], respectively. The results of model-fitting analysis indicated that the additive genetic and individual-specific environmental effects were 72% [95% CI (67%, 76%)] and 28% [95% CI (24%, 33%)], respectively. Neither nonadditive genetic nor shared environmental effects were significant.

Cataract, defined as opacity of the lens in one or both eyes, is a major cause of blindness throughout the world, and not uncommon, particularly in the elderly population. However, congenital cataracts are rare and occur with a frequency of 30 cases in 100,000 births. About one-third of the cases fall into the group inherited without systemic abnormality. Importantly, congenital cataracts produce deprivation amblyopia, refractive amblyopia, and retinal detachment, leading to lifelong visual impairment. Successful management is dependent on early diagnosis and referral for surgery when indicated. Here we present a case of hereditary bilateral cataracts in a dizygotic twin detected on prenatal ultrasound examinations and postnatally confirmed as congenital cataracts associated with posterior lenticonus.

Background: Exaggerated cardiovascular reactivity to stressful stimuli may be a risk factor for the development of hypertension. The genetic influence on blood pressure (BP) reactivity to stress and its control mechanisms has been receiving considerable support. This study aims at examining the heritability of BP and its intermediate hemodynamic phenotypes to acute stress in a homogeneous Arab population. Methods: Parameters were computed from continuous BP, electrocardiography and impedance cardiography measurements, during rest, word conflict (WCT) and cold pressor (CPT) tests. Heritability estimates (h2) were obtained using the variance components-based approach implemented in the SOLAR software package. Results: Reactivity scores for WCT and CPT increased significantly (P < .05) for systolic (SBP), diastolic (DBP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR). They decreased significantly (P < .05) for stroke volume (SV), left ventricular ejection time (LVET), end diastolic (EDI) and cardiac contractility (IC) indices. Univariate analysis detected heritability estimates that ranged from 0.19–0.35 for rest, 0.002–0.40 for WCT and 0.08–0.35 for CPT. Conclusion: In this unique cohort, resting as well as challenged cardiovascular phenotypes are significantly influenced by additive genetic effects. Heritability estimates for resting phenotypes are in a relatively narrow range, while h2 for their reactivity is somewhat broader with lower estimates. Further analyses of this study may offer important opportunities for gene finding in hypertension. What is Known About the Topic: (1) cardiovascular reactivity to stress predicts cardiovascular disease; (2) genetic susceptibility plays an important role in stress reactivity. Family studies using the cold pressure test reported significant heritability for blood pressure. What this Study Adds: (1) this cohort is from five highly consanguineous isolated Arab pedigrees with genetically verified genealogical records and environmental homogeneity; (2) This is the first study to estimate heritability of detailed intermediate hemodynamic phenotypes that make up normal blood pressure.

The aim was to analyse the neonatal mortality related to mode of delivery for twins using a population-based registry. In all, 18,125 twins delivered in Sweden between 1991 and 1997, after excluding those with unknown gestational duration, were used to analyse the differences between groups of twins. Results showed the OR for neonatal death, breech vaginal delivery versus caesarean section (all indications) was 1.47 (95% CI 0.99-2.17). The OR at vaginal delivery for neonatal death, twin I in breech versus cephalic presentation was 5.60 (2.62-11.94) and for twin II the corresponding figures were 1.85 (1.03-3.32). Analyses using population-based registries from other countries are needed to confirm or reject the present findings of an increased neonatal mortality for twins in breech presentation delivered vaginally.

Chronic widespread pain (CWP) is a common disorder affecting up to 15% of the general population. The objective of the present study was to explore the role of previously reported psychosocial and interpersonal risk factors on variation in CWP by investigating CWP discordant monozygotic (MZ) twins. This approach allows separation of cause and effect relationships, albeit imperfectly, as well the control for critical confounding variables such as common environment or genetics. In a total sample of N = 3,266 female twins aged 18–89 years, MZ (113 full pairs) and DZ twins (180 full pairs) discordant for CWP were selected. Items from the London fibromyalgia symptom screening questionnaire were used to discriminate cases from controls. To assess potential risk factors, including body mass index, anxiety sensitivity (AS), emotional intelligence, personality, obsessive-compulsive behavior, and coping, validated questionnaires were used. A set of univariate and multivariate logistic regression analyses were conducted. Of the variables showing significant links with CWP in the univariate individual-level analyses, including age, AS, and emotional intelligence, only emotional intelligence turned out to an independent predictor to the pathogenesis of CWP in both the individual level and discordant MZ analyses. These data indicate that in women having identical genetic risk, emotional intelligence seems to play a key role, although of small effect, in the development and/or maintenance of CWP. It further seems that many of the previously reported risk factors for CWP suffer from genetic confounding.