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Loneliness is related to mental and somatic health outcomes, including borderline personality disorder. Here, we analyze the sources of variation that are responsible for the relationship between borderline personality features (including four dimensions, affective instability, identity disturbance, negative relationships, self-harm and a total score) and loneliness. Using genetically informative data from two large nonclinical samples of adult twin pairs from Australia and the Netherlands (N = 11,329), we estimate the phenotypic, genetic and environmental correlations between self-reported borderline personality features and loneliness. Individual differences in borderline personality and loneliness were best explained by additive genetic factors with heritability estimates h2 = 41% for the borderline personality total score and h2 = 36% for loneliness, with the remaining variation explained by environmental influences that were not shared by twins from the same pair. Genetic and environmental factors influencing borderline personality (total score and four subscales separately) were also partial causes of loneliness. The correlation between loneliness and the borderline personality total score was rph = .51. The genetic correlation was estimated at rg = .64 and the environmental correlation at re = .40. Our study suggests common etiological factors in loneliness and borderline personality features.
The aim of this study was to evaluate the differences in the metabolic profile and body composition of monozygotic (MZ) twins concordant and discordant for the practice of physical exercise. The sample consisted of 92 MZ twins (72.5% female and 27.5% male, mean age 25.4 ± 5.69 years), registered with the Brazilian Registry of Twins, residing in Natal, Brazil. Data collection was carried out between the years 2016 and 2018. On day 1, subjects underwent a whole-body fitness evaluation, including measures of weight, height, body composition by Dual-Energy X-ray Absorptiometry and the Cardiorespiratory Exercise Test. On day 2, 10 ml blood samples were collected (overnight fasting) to determine the lipid profile and fasting glucose. The sample was separated into three groups: Active Concordant twins (Concordant A, n = 44 subjects), Inactive Concordant twins (Concordant I, n = 22 subjects) and Discordant pairs for Physical Exercise (Discordant PE, n = 26 subjects). The results demonstrated a difference between the discordant twins for exercise and also between the active versus sedentary groups, indicating a causal effect of exercise on the fat percentage, maximum oxygen consumption (VO2max) and second ventilatory threshold variables. Between groups, a difference was also observed between the groups in ventilatory threshold, very low-density lipoprotein and triglycerides. We concluded that, regardless of genetics, the practice of physical exercise was sufficient to generate alterations in body composition and VO2max in MZ twins, but not in the lipid profile or fasting glucose.
Much of the focus of personality disorder genetics has been aimed at identifying putative genes. Most of the research has been accomplished using a classical monozygotic and dizygotic twin design or adoption study methodologies. This vast body of research has repeatedly shown that the observed variability in personality disorder measures are directly attributable to the action of genes, but few, if any genetic loci have been reliably identified. The chapter explores the reasons for this failure such as the impact of a grand unitary theory of personality function that has created concepts and measures that are poorly suited for genetic studies. Moreover, there are inherent problems in genetic methodology, despite the faith in the latest gene hunting methods that have not been able to overcome psychometric and conceptual issues with personality constructs and measures. Indeed, attempts to revise measures and diagnostic entities have likely exacerbated the problems. Suggestions to overcome these issues, from shifting focus from descriptive personality constructs to active personality constructs such as behavioral choice, the development of personality endophenotypes, and new methods to incorporate data from unrelated individuals in gene hunting studies to increase power and detect small effects of multiple genes are discussed.
To investigate the association of folic acid (FA) supplementation with birth weight, the risk of small for gestational age (SGA) and low birth weight (LBW) in singleton and twin pregnancy.
A population-based cross-sectional survey.
Twenty counties and ten districts in Shaanxi Province of northwestern China, 2013.
28 174 pregnant women with their infants, covering 27 818 single live births and 356 twin live births.
The prevalence of FA supplementation in singletons and twins was 63·9 and 66·3 %. The mean birth weight was 3267 (sd 459·1) g, 2525 (sd 534·0) g and 2494 (sd 539·5) g; the prevalence of SGA was 14·3, 51·4 and 53·4 %; the prevalence of LBW was 3·4, 42·4 and 46·6 % among singleton, twin A and twin B, respectively. Compared with non-users, women with FA supplementation were (β 17·3, 95 % CI 6·1, 28·4; β 166·3, 95 % CI 69·1, 263·5) associated with increased birth weight, lower risk of SGA (OR 0·85, 95 % CI 0·80, 0·92; OR 0·45, 95 % CI 0·30, 0·68) and LBW (OR 0·82, 95 % CI 0·71, 0·95; OR 0·50, 95 % CI 0·33, 0·75) in singletons and twins, and more prominent effects in twins. Moreover, there were significant interactions between FA supplementation and plurality on birth weight, SGA and LBW.
The present study suggests the association of periconceptional 0·4 mg/d FA supplementation with increased birth weight and reduced risk of SGA and LBW in both singletons and twins, and this association may be more prominent in twins.
Previous studies have suggested altered structural and functional asymmetry of the brain in schizophrenia.
Functional MRI was used to assess differences in cortical activation during a verbal task in Broca's area and its contralateral homologue in four pairs of right-handed monozygotic (MZ) twins discordant and concordant for schizophrenia with low and high familial loading for the illness and four healthy control MZ twin pairs.
Pooled data from all subjects with schizophrenia showed increased activation in the right homologue of Broca's area in contrast to healthy individuals. Concordant twins (i.e. high familial loading group) showed prominent between co-twin differences in lateralization index within given region of interest. Intra-pair differences in lateralization index were significantly higher in concordant twins compared to the controls (0.69 ± 0.4 vs. 0.13 ± 0.13, P < 0.03), albeit no significant differences in the variable were shown between the discordant and control groups.
This study provides evidence of reduced cerebral dominance for language processing in patients with schizophrenia. The findings further suggest the need for additional research on relative proportion of genetic and environmental factors underlying deviations of functional asymmetry in schizophrenia.
Schizophrenia is associated with altered neural development. We assessed neurological soft signs (NSS) and dermatoglyphic anomalies (total a–b ridge count (TABRC) and total finger ridge count) in 15 pairs of twins concordant and discordant for schizophrenia. Within-pair differences in both NSS and TABRC scores were significantly greater in discordant compared to concordant monozygotic pairs. There was no significant difference in NSS and TABRC scores between subjects with schizophrenia and their co-twins without the illness. However, monozygotic discordant twins with schizophrenia had higher ABRCs on their right hands compared to their co-twins without the illness. These findings suggest that an unidentified environmental event acting between weeks 6 and 15 of gestation affects the development of monozygotic twins who go on to develop schizophrenia but does not have a corresponding effect on their co-twins who do not develop the illness. The effect of such an event on dermatoglyphic profiles appears lateralised to the right hand in affected twins.
T1 and T2 relaxation times were examined in four pairs of monozygotic (MZ) twins discordant and concordant for schizophrenia with low and high genetic loading for the illness and five healthy control MZ twin pairs. Patients with schizophrenia (n = 11) showed significant prolongation in T1 relaxation times in the globus pallidus (GP) bilaterally (P < 0.005, Bonferroni corrected) when compared to 14 healthy MZ twins.
Though cognitive abilities in adulthood are largely influenced by individual genetic background, they have also been shown to be importantly influenced by environmental factors. Some of these influences are mediated by epigenetic mechanisms. Accordingly, polymorphic variants in the epigenetic gene DNMT3B have been linked to neurocognitive performance. Since monozygotic (MZ) twins may show larger or smaller intrapair phenotypic differences depending on whether their genetic background is more or less sensitive to environmental factors, a twin design was implemented to determine if particular polymorphisms in the DNMT3B gene may be linked to a better (worse) response to enriched (deprived) environmental factors.
Applying the variability gene methodology in a sample of 54 healthy MZ twin pairs (108 individuals) with no lifetime history of psychopathology, two DNMT3B polymorphisms were analyzed in relation to their intrapair differences for either intellectual quotient (IQ) or working memory performance.
MZ twin pairs with the CC genotype for rs406193 SNP showed statistically significant larger intrapair differences in IQ than CT pairs.
Results suggest that DNMT3B polymorphisms may explain variability in the IQ response to either enriched or impoverished environmental conditions. Accordingly, the applied methodology is shown as a potentially valuable tool for determining genetic markers of cognitive plasticity. Further research is needed to confirm this specific result and to expand on other putative genetic markers of environmental sensitivity.
To test whether firstly, different parental rearing components were associated with different dimensions of psychiatric symptoms in adulthood, secondly BDNF-Val66Met polymorphism moderated this association and thirdly, this association was due to genetic confounding.
Perceived parental rearing according to Parental Bonding Instrument (PBI), psychiatric symptoms evaluated with the Brief Symptom Inventory (BSI) and the BDNF-Val66Met polymorphism were analyzed in a sample of 232 adult twins from the general population.
In the whole sample, paternal care was negatively associated with depression. Maternal overprotection was positively associated with paranoid ideation, obsession-compulsion and somatization. Gene-environment interaction effects were detected between the BDNF-Val66Met polymorphism and maternal care on phobic anxiety, paternal care on hostility, maternal overprotection on somatization and paternal overprotection also in somatization. In the subsample of MZ twins, intrapair differences in maternal care were associated with anxiety, paranoid ideation and somatization.
Met carriers were, in general, more sensitive to the effects of parental rearing compared to Val/Val carriers in relation to anxiety and somatization. Contra-intuitively, our findings suggest that high rates of maternal care might be of risk for Met carriers regarding anxiety. Results from analyses controlling for genetic confounding were in line with this finding.
Quantitative genetic research includes a range of genetically sensitive research designs that rely on family samples to study the relative importance of genes and environments for individual difference in psychopathology. The past decades have seen an increase in quantitative genetic research focused on the origins of childhood and adolescent psychopathology. Evidence from this research univocally demonstrates that genetic factors play an important role in all forms of psychopathology, and that these genetic factors interact with the environment to shape the development of childhood and adolescent psychopathology. The goal of this chapter is to highlight how recent methodological developments and the accumulation of longitudinal data now allow quantitative genetic research to go beyond asking “if” genetic factors are important, to instead address important questions regarding gene-environment interplay in the development of childhood and adolescent psychopathology. It begins by introducing the family, adoption, and twin designs, and summarizing the main findings from these methods for child and adolescent psychopathology. It then provides concrete examples of how multivariate and longitudinal quantitative genetic research designs can be used to address important questions regarding etiology across different levels of symptom severity, comorbidity, and development, and to study gene-environment interplay in child and adolescent psychopathology. It concludes by highlighting important outstanding questions in childhood psychopathology that need to be addressed in future quantitative genetic research.
Nick Martin was a doctoral student of mine at the University of Birmingham in the mid 1970s. In this review, I discuss two of Nick’s earliest and most seminal contributions to the field of behavior genetics. First, Martin and Eaves’ (1977) extension of the model-fitting approach to multivariate data, which laid the theoretical groundwork for a generation of multivariate behavior genetic studies. Second, the Martin et al.’s (1978) manuscript on the power of the classical twin design, which showed that thousands of twin pairs would be required in order to reliably estimate components of variance, and has served as impetus for the formation of large-scale twin registries across the world. I discuss these contributions against the historical backdrop of a time when we and others were struggling with the challenge of figuring out how to incorporate gene-by-environment interaction, gene–environment correlation, mate selection and cultural transmission into more complex genetic models of human behavior.
There is growing evidence of an association between negative social comparisons (NSC) and both psychosis, and psychosis proneness. The majority of the work thus far, however, has focused largely on one type of NSC, namely, social rank. Whilst social rank is clearly an important factor, an individual's perception of belonging is likely also of importance; particularly, when considering individuals from collectivistic cultures such as China, where greater emphasis is placed on fitting into the group. There is also limited research investigating what factors may contribute towards the relationship between NSC and psychosis proneness, and to what extent this relationship may be due to common familial factors. To address these issues, we examined whether (1) Social rank and perceived belonging predict negative, positive and depressive psychotic experiences in a Chinese, adolescent, twin and sibling population, (2) coping styles moderate the impact of these relationships and (3), there is a familial association between NSC and psychosis proneness. Both social rank and perceived belonging were found to predict the negative and depressive dimensions of psychosis. These relationships were moderated by problem-focused coping styles. Interestingly, the association between perception of belonging, and negative psychotic experiences was familial—and stronger in Monozygotic twins—indicating perhaps shared aetiology due to common genes. Our findings highlight NSC as potential vulnerability markers for negative and depressive psychotic experiences, and suggest potentially different aetiological pathways amongst different NSC and different psychotic experiences. On a clinical level, our findings emphasize the need to consider coping styles when treating at-risk individuals.
Depressive episodes experienced in unipolar (UD) and bipolar (BD) disorders are characterized by anhedonia and have been associated with abnormalities in reward processes related to reward valuation and error prediction. It remains however unclear whether these deficits are associated with familial vulnerability to mood disorders.
In a functional magnetic resonance imaging study, we evaluated differences in the expected value (EV) and reward prediction error (RPE) signals in ventral striatum (VS) and prefrontal cortex between three groups of monozygotic twins: affected twins in remission for either UD or BD (n = 53), their high-risk unaffected co-twins (n = 34), and low-risk twins with no family history of mood disorders (n = 25).
Compared to low-risk twins, affected twins showed lower EV signal bilaterally in the frontal poles and lower RPE signal bilaterally in the VS, left frontal pole and superior frontal gyrus. The high-risk group did not show a significant change in the EV or RPE signals in frontostriatal regions, yet both reward signals were consistently lower compared with low-risk twins in all regions where the affected twins showed significant reductions.
Our findings strengthen the notion that reduced valuation of expected rewards and reduced error-dependent reward learning may underpin core symptom of depression such as loss of interest in rewarding activities. The trend reduction in reward-related signals in unaffected co-twins warrants further investigation of this effect in larger samples and prospective follow-up to confirm possible association with increased familial vulnerability to mood disorders.
Using vital statistics in Japan (1995–2008), 154,578 live-born twin pairs (128,236 monozygotic [MZ] and 180,920 dizygotic [DZ]) were identified. The proportion of severe discordance among live-born twin births was twice as high in Japanese than Caucasian infants. There were 1858 MZ and 1620 DZ infant deaths. Computation of the relationship between infant mortality rate and birth weight discordance among the twins was performed. Discordance levels were classified into seven groups: <5%, five groups from 5–9% to 25–29%, and ≥30%.The mortality rate was significantly higher in MZ than DZ twins for discordances except at 5–9% and 10–14%. The lowest rate for MZ twins was at 5–9% (7.5 per 1000 live twins) and significantly increased from 10–14% (9.4) to ≥30% (83.4), while the lowest rate for DZ twins was at <5% (6.7), which significantly increased at 10–14% (8.0) and from 25–29% (12.1) to ≥30% (35.5). The relationship was also computed in two gestational age groups (<28 and ≥28 weeks). For births at <28 weeks, three discordances (after 20–24%) in MZ twins were associated with adverse mortality rate. For births at ≥28 weeks, the same relationship was obtained after 10–14% in MZ and after 20–24% in DZ twins. The relationship from 2002 to 2008 showed that the mortality rates significantly increased after 10–14% for both types of twins. In conclusion, five discordance levels in MZ and three levels in DZ twins were associated with adverse mortality rates.
Type 2 diabetes, which is caused by both genetic and environmental factors, may be diagnosed using the oral glucose tolerance test (OGTT). Recent studies demonstrated specific patterns in glucose curves during OGTT associated with cardiometabolic risk profiles. As the relative contribution of genetic and environmental influences on glucose curve patterns is unknown, we aimed to investigate the heritability of these patterns. We studied twins from the Danish GEMINAKAR cohort aged 18–67 years and free from diabetes at baseline during 1997–2000; glucose concentrations were measured three times during a 2-h OGTT. Heterogeneity of the glucose response during OGTT was examined with latent class mixed-effects models, evaluating goodness of fit by Bayes information criterion. The genetic influence on curve patterns was estimated using quantitative genetic modeling based on linear structural equations. Overall, 1455 twins (41% monozygotic) had valid glucose concentrations measured from the OGTT, and four latent classes with different glucose response patterns were identified. Statistical modeling demonstrated genetic influence for belonging to a specific class or not, with heritability estimated to be between 45% and 67%. During ∼12 years of follow-up, the four classes were each associated with different incidence of type 2 diabetes. Hence, glucose response curve patterns associated with type 2 diabetes risk appear to be moderately to highly heritable.
Scholarly literature claims that health declines in populations when optimism about investing in the future wanes. This claim leads us to describe collective optimism as a predictor of selection in utero. Based on the literature, we argue that the incidence of suicide gauges collective optimism in a population and therefore willingness to invest in the future. Using monthly data from Sweden for the years 1973–2016, we test the hypothesis that the incidence of suicide among women of child-bearing age correlates inversely with male twin births, an indicator of biological investment in high-risk gestations. We find that, as predicted by our theory, the incidence of suicide at month t varies inversely with the ratio of twin to singleton male births at month t + 3. Our results illustrate the likely sensitivity of selection in utero to change in the social environment and so the potential for viewing collective optimism as a component of public health infrastructure.
In 1984, Hrubec and Robinette published what was arguably the first review of the role of twins in medical research. The authors acknowledged a growing distinction between two categories of twin studies: those aimed at assessing genetic contributions to disease and those aimed at assessing environmental contributions while controlling for genetic variation. They concluded with a brief section on recently founded twin registries that had begun to provide unprecedented access to twins for medical research. Here we offer an overview of the twin research that, in our estimation, best represents the field has progress since 1984. We start by summarizing what we know about twinning. We then focus on the value of twin study designs to differentiate between genetic and environmental influences on health and on emerging applications of twins in multiple areas of medical research. We finish by describing how twin registries and networks are accelerating twin research worldwide.
The Vietnam Era Twin Study of Aging (VETSA) is a longitudinal behavioral genetic study with a primary focus on cognitive and brain aging in men, particularly early identification of risk for mild cognitive impairment (MCI) and Alzheimer’s disease (AD). It comprises a subset of over 1600 twins from the Vietnam Era Twin Registry. Twins live all over the USA. Assessments began when participants were in their 50s. Follow-ups were conducted every 5–6 years, and wave 3 has been completed as of this writing. The age range of participants is narrow (about 10 years). An extensive neurocognitive test battery has added precision in assessing differences in middle-aged adults, and predicting progression to MCI. Young adult cognitive test data (at an average age of 20 years) provide a means of disentangling aging effects from longstanding differences. Genome wide genotyping and plasma assays of AD biomarkers from waves 1 and 3 were conducted in wave 3. These features make the VETSA ideal for studying the heterogeneity of within-individual trajectories from midlife to old age, and for early detection of risk factors for cognitive decline.
The Wisconsin Twin Project encompasses nearly 30 years of longitudinal research that spans infancy to early adulthood. The twin sample was recruited from statewide birth records for birth cohorts 1989–2004. We summarize early recruitment, assessment, retention and recently completed twin neuroimaging studies. In addition to the focal twins, longitudinal data were also collected from two parents and nontwin siblings. Our adolescent and young adult neuroimaging sample (N = 600) completed several previous behavioral and environmental assessments, beginning shortly after birth. The extensive phenotyping is meant to support a range of empirical investigations with potentially differing theoretical perspectives.