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Twin Research and Human Genetics : the... Jun 2015All same-sex dizygotic (DZ) twins and approximately one-third of monozygotic (MZ) twin pairs have separate placentas, making it impossible to use the number of placentas... (Comparative Study)
Comparative Study
All same-sex dizygotic (DZ) twins and approximately one-third of monozygotic (MZ) twin pairs have separate placentas, making it impossible to use the number of placentas to determine zygosity. Zygosity determination is further complicated because incorrect assumptions are often made, such as that only DZ pairs have two placentas and that all MZ pairs are phenotypically identical. These assumptions, by twins, their families and health professionals, along with the lack of universal zygosity testing for same-sex twins, has led to confusion within the twin community, yet little research has been conducted with twins about their understanding and assumptions about zygosity. We aimed to explore and quantify understanding and assumptions about zygosity using twins attending an Australian twin festival. We recruited 91 twin pairs younger than 18 years of age and their parents, and 30 adult twin pairs who were all uncertain of their zygosity, to complete one pen and paper questionnaire and one online questionnaire about their assumed zygosity, reasons for their assumptions and the importance of accurate zygosity knowledge. Responses were compared with their true zygosity measured using a genetic test. We found a substantial proportion of parents and twins had been misinformed by their own parents or medical professionals, and that knowledge of their true zygosity status provided peace of mind and positive emotional responses. For these reasons we propose universal zygosity testing of same-sex twins as early in life as possible and an increase in education of medical professionals, twins and families of twins about zygosity issues.
Topics: Adolescent; Adult; Aged; Attitude to Health; Child; Child, Preschool; Cohort Studies; DNA; Disclosure; Emotions; Exploratory Behavior; Female; Genotype; Human Rights; Humans; Infant; Male; Middle Aged; Parents; Patient Access to Records; Self Concept; Sibling Relations; Twins, Dizygotic; Twins, Monozygotic; Victoria; Young Adult
PubMed: 25851727
DOI: 10.1017/thg.2015.15 -
European Journal of Endocrinology Jun 2022Type 1 diabetes and Hashimoto's thyroiditis frequently cluster in individuals and in families, indicating shared origins. The objective of this study was to investigate...
OBJECTIVE
Type 1 diabetes and Hashimoto's thyroiditis frequently cluster in individuals and in families, indicating shared origins. The objective of this study was to investigate familial co-aggregation of these diseases and to quantify shared genetic and environmental factors.
DESIGN
This study is a twin cohort study.
METHODS
National health registers were used to identify cases among 110 814 Swedish twins. Co-aggregation was calculated as risk ratios for type 1 diabetes among co-twins of individuals with Hashimoto's thyroiditis, and vice-versa. Variance explained by genetics (i.e. heritability), and the proportions thereof shared between the diseases, was estimated by contrasting associations in monozygotic and dizygotic twins using structural equation models.
RESULTS
Individuals with one disease were at a high risk for the other disease (adjusted risk ratio: 11.4 (95% CI: 8.5-15.3)). Co-aggregation was more common in monozygotic than in dizygotic pairs, with adjusted risk ratios of 7.0 (95% CI: 3.2-15.1) and 1.7 (95% CI: 0.7-4.1), respectively. Genetic effects shared across diseases accounted for 11% of the variance for type 1 diabetes and 9% of the variance for Hashimoto's thyroiditis, while environmental factors unique to individual twins, but shared across diseases, accounted for 10% of the variance for type 1 diabetes and 18% of the variance for Hashimoto's thyroiditis.
CONCLUSIONS
Both genes and environment unique to individual twins contribute to considerable etiologic overlap between type 1 diabetes and Hashimoto's thyroiditis. These findings add to the current knowledge on the mechanisms behind autoimmune disease clustering and could guide future research aimed at identifying pathophysiological mechanisms and intervention targets.
Topics: Humans; Diabetes Mellitus, Type 1; Cohort Studies; Hashimoto Disease; Twins, Dizygotic; Autoimmune Diseases
PubMed: 36321757
DOI: 10.1530/EJE-22-0025 -
Behavior Genetics Jan 2024Nutrition and diet are key modifiable risk factors for the rising burden of non-communicable diseases like cardio-vascular diseases and diabetes in low- and middle-...
Nutrition and diet are key modifiable risk factors for the rising burden of non-communicable diseases like cardio-vascular diseases and diabetes in low- and middle- income countries (LMICs). The nutritional transition in dietary behaviours in LMICs has most likely contributed to this problem. Although traditionally assumed to be environmental, dietary choices are also genetically influenced. Twin study designs can be used to investigate the relative influence of genes and environment on nutrition intake, eating behaviours and associated psychological health. The overall aim of this project is to: provide proof-of-concept for the feasibility of using dietary (biomarker) data within the Children-of-Twin design in nutrition studies, develop laboratory skills and statistical genetic skills and establish a Sri Lankan-specific food composition database. Currently, a pilot study is being conducted with 304 individuals (38 Monozygotic twin pairs, 38 Dizygotic twin pairs and their male or female adult offspring). Questionnaire data on nutritional intake, eating behaviours, psychological well-being, physical health, and bio-specimens are being collected. A Sri Lankan-specific food composition database was developed, training sessions on macro and micro element analysis in biological samples and statistical genetics skills development were conducted and Community Engagement and Involvement programs were carried out in two districts of Sri Lanka.
Topics: Adult; Female; Humans; Male; Diseases in Twins; Feasibility Studies; Pilot Projects; Twins, Dizygotic; Twins, Monozygotic; Adult Children
PubMed: 38184818
DOI: 10.1007/s10519-023-10171-w -
JAMA Network Open Aug 2022Although infancy is the most rapid period of postnatal growth and development, factors associated with variation in infant traits are not well understood. (Meta-Analysis)
Meta-Analysis
IMPORTANCE
Although infancy is the most rapid period of postnatal growth and development, factors associated with variation in infant traits are not well understood.
OBJECTIVE
To synthesize the large twin study literature partitioning phenotypic variance in psychological traits and developmental milestones in infancy into estimates of heritability and shared and nonshared environment.
DATA SOURCES
PubMed, PsycINFO, and references of included publications were searched up to February 11, 2021.
STUDY SELECTION
Peer-reviewed publications using the classical twin design to study psychological traits and developmental milestones from birth to 2 years old were included.
DATA EXTRACTION AND SYNTHESIS
Data were extracted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses and categorized using the International Classification of Functioning, Disability and Health: Children and Youth Version. Data were pooled in 3-level random effects models, incorporating within-cohort variance in outcome measurement and between-cohort variance. Data were analyzed from March 2021 through September 2021.
MAIN OUTCOMES AND MEASURES
The primary outcomes were monozygotic and dizygotic twin correlations. These were used to calculate genetic and shared and nonshared environment estimates.
RESULTS
Among 139 publications that were systematically retrieved, data were available on 79 044 twin pairs (31 053 monozygotic and 47 991 dizygotic pairs), 52 independent samples, and 21 countries. Meta-analyses were conducted on psychological traits and developmental milestones from 106 publications organized into 10 categories of functioning, disability, and health. Moderate to high genetic estimates for 8 categories were found, the highest of which was psychomotor functions (pooled h2, 0.59; 95% CI, 0.25-0.79; P < .001). Several categories of traits had substantial shared environment estimates, the highest being mental functions of language (pooled c2, 0.59; 95% CI, 0.24-0.86; P = .001). All examined categories of traits had moderate or high nonshared environment estimates, the highest of which were emotional functions (pooled e2, 0.42; 95% CI, 0.33-0.50; P < .001) and family relationships (pooled e2, 0.42; 95% CI, 0.30-0.55; P < .001).
CONCLUSIONS AND RELEVANCE
These findings may be an important source of information to guide future gene discovery research, public perspectives on nature and nurture, and clinical insights into the degree to which family history and environments may estimate major domains of infant functioning, disability, and health in psychological traits and developmental milestones.
Topics: Adolescent; Child; Cohort Studies; Forecasting; Humans; Infant; Phenotype; Twins, Dizygotic
PubMed: 35994288
DOI: 10.1001/jamanetworkopen.2022.27887 -
Behavior Genetics Mar 2017We compared the nature of the sibling relationship in dyads of varying genetic relatedness, employing a behavioural genetic design to estimate the contribution that...
We compared the nature of the sibling relationship in dyads of varying genetic relatedness, employing a behavioural genetic design to estimate the contribution that genes and the environment have on this familial bond. Two samples were used-the Sisters and Brothers Study consisted of 173 families with two target non-twin children (mean ages = 7.42 and 5.22 years respectively); and the Twins, Family and Behaviour study included 234 families with two target twin children (mean age = 4.70 years). Mothers and fathers reported on their children's relationship with each other, via a postal questionnaire (the Sisters and Brothers Study) or a telephone interview (the Twins, Family and Behaviour study). Contrary to expectations, no mean level differences emerged when monozygotic twin pairs, dizygotic twin pairs, and non-twin pairs were compared on their sibling relationship quality. Behavioural genetic analyses also revealed that the sibling bond was modestly to moderately influenced by the genetic propensities of the children within the dyad, and moderately to substantially influenced by the shared environment common to both siblings. In addition, for sibling negativity, we found evidence of twin-specific environmental influence-dizygotic twins showed more reciprocity than did non-twins. Our findings have repercussions for the broader application of results from future twin-based investigations.
Topics: Adult; Child; Child, Preschool; Environment; Fathers; Female; Genetics, Behavioral; Humans; Male; Mothers; Siblings; Social Behavior; Social Environment; Surveys and Questionnaires; Twins; Twins, Dizygotic; Twins, Monozygotic
PubMed: 27796609
DOI: 10.1007/s10519-016-9825-z -
Developmental Psychology Jul 2018There is little research to date on the academic implications of teaching twins in the same or different classroom. Consequently, it is not clear whether twin classroom...
There is little research to date on the academic implications of teaching twins in the same or different classroom. Consequently, it is not clear whether twin classroom separation is associated with positive or negative educational outcomes. As a result, parents and teachers have insufficient evidence to make a well-informed decision when twins start school. This study addresses two research questions: Are there average positive or negative effects of classroom separation? Are twins taught in different classes more different from each other than twins taught in the same class? Twin pairs from two large representative samples from Quebec (Canada) and the United Kingdom were evaluated across a large age range (7 to 16 years) on academic achievement, several cognitive abilities and motivational measures. Our results show almost no sizable positive or negative average effect of classroom separation on twins' achievement, cognitive ability and motivation. Twin pairs at age 12 (Quebec, Canada) and at age 16 (United Kingdom) were slightly more similar on achievement if placed in the same classroom, with slightly greater similarity among monozygotic twins than dizygotic twins. However, the few effects found were weak, and it remains unclear whether they result from classroom separation or other factors. These results suggest that in terms of educational outcomes, policymakers should not impose rigid guidelines to separate twin pairs during their education. The choice of whether to educate twin pairs together or separately should be up to parents, twins and teachers, in response to twins' individual needs. (PsycINFO Database Record
Topics: Academic Success; Adolescent; Analysis of Variance; Child; Cognition; Female; Humans; Male; Motivation; Psychological Tests; Psychology, Child; Schools; Sibling Relations; Social Behavior; Twins, Dizygotic; Twins, Monozygotic
PubMed: 29658740
DOI: 10.1037/dev0000519 -
Biodemography and Social Biology 2022Data from the Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium were used to examine predictions of different models of gene-by-environment...
Data from the Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium were used to examine predictions of different models of gene-by-environment interaction to understand how genetic variance in self-rated health (SRH) varies at different levels of financial strain. A total of 11,359 individuals from 10 twin studies in Australia, Sweden, and the United States contributed relevant data, including 2,074 monozygotic and 2,623 dizygotic twin pairs. Age ranged from 22 to 98 years, with a mean age of 61.05 (SD = 13.24). A factor model was used to create a harmonized measure of financial strain across studies and items. Twin analyses of genetic and environmental variance for SRH incorporating age, age, sex, and financial strain moderators indicated significant financial strain moderation of genetic influences on self-rated health. Moderation results did not differ across sex or country. Genetic variance for SRH increased as financial strain increased, matching the predictions of the diathesis-stress and social comparison models for components of variance. Under these models, environmental improvements would be expected to reduce genetically based health disparities.
Topics: Adult; Aged; Aged, 80 and over; Disease Susceptibility; Humans; Middle Aged; Sweden; Twins, Dizygotic; United States; Young Adult
PubMed: 35156881
DOI: 10.1080/19485565.2022.2037069 -
Perspectives on Psychological Science :... Nov 2023What are the major sources of worldwide variability in subjective well-being (SWB)? Twin and family studies of SWB have found substantial heritability and strong effects...
What are the major sources of worldwide variability in subjective well-being (SWB)? Twin and family studies of SWB have found substantial heritability and strong effects from unique environments but virtually no effects from shared environments. However, extant findings are not necessarily valid at the global level. Prior studies have examined within-countries variability but did not take into account mean differences across nations. In this article, we aim to estimate the effects of genetic factors, individual environmental exposures, and shared environments for the global population. We combine a set of knowns from national well-being studies (means and standard deviations) and behavioral-genetic studies (heritability) to model a scenario of twin studies across 157 countries. For each country, we simulate data for a set of twin pairs and pool the data into a global sample. We find a worldwide heritability of 31% to 32% for SWB. Individual environmental factors explain 46% to 52% of the variance (including measurement error), and shared environments account for 16% to 23% of the global variance in SWB. Worldwide, well-being is somewhat less heritable than within nations. In contrast to previous within-countries studies, we find a notable effect of shared environments. This effect is not limited to within families but operates at a national level.
Topics: Humans; Twins, Dizygotic; Twins, Monozygotic; Environmental Exposure; Gene-Environment Interaction; Genetics
PubMed: 37384562
DOI: 10.1177/17456916231178716 -
Journal of the American Academy of... Feb 2019Psychotic experiences (PE) are dimensional phenomena in the general population that resemble psychotic symptoms, such as paranoia and hallucinations. This is the first...
OBJECTIVE
Psychotic experiences (PE) are dimensional phenomena in the general population that resemble psychotic symptoms, such as paranoia and hallucinations. This is the first twin study to explore the degree to which tobacco use and PE share genetic or environmental influences. Previous studies on the association between adolescent tobacco use and PE have not considered PE dimensionally, included negative symptoms, or accounted for confounding by sleep disturbance and stressful life events.
METHOD
An unselected adolescent twin sample (N = 3,787 pairs; mean age = 16.16 years) reported on PE (paranoia, hallucinations, cognitive disorganization, grandiosity, and anhedonia) and regularity of tobacco use. Parents rated the twins' negative symptoms. Regression analyses were conducted while adjusted for sociodemographic characteristics, prenatal maternal smoking, cannabis use, sleep disturbance, and stressful life events. Bivariate twin modeling was used to estimate the degree of genetic and common and unique environmental influences shared between tobacco use and PE.
RESULTS
Regular smokers were significantly more likely to experience paranoia, hallucinations, cognitive disorganization, and negative symptoms (β = 0.17-0.34), but not grandiosity or anhedonia, than nonsmokers, after adjustment for confounders. Paranoia, hallucinations, and cognitive disorganization correlated ≥0.15 with tobacco use (r = 0.15-0.21, all p < .001). Significant genetic correlations (r=0.37-0.45) were found. Genetic influences accounted for most of the association between tobacco use and paranoia (84%) and cognitive disorganization (81%). Familial influences accounted for 80% of the association between tobacco use and hallucinations.
CONCLUSION
Tobacco use and PE during adolescence were associated after adjustment for confounders. They appear to co-occur largely because of shared genetic influences.
Topics: Adolescent; Female; Genetic Predisposition to Disease; Hallucinations; Humans; Male; Psychotic Disorders; Regression Analysis; Tobacco Use; Twins, Dizygotic; Twins, Monozygotic; United Kingdom
PubMed: 30738553
DOI: 10.1016/j.jaac.2018.06.037 -
Obesity Facts 2023While the genetic and environmental underpinnings of body weight and alcohol use are fairly well-known, determinants of simultaneous changes in these traits are still...
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.
Topics: Adult; Female; Humans; Male; Alcohol Drinking; Body Mass Index; Cohort Studies; Longitudinal Studies; Twins, Dizygotic; Twins, Monozygotic
PubMed: 36882010
DOI: 10.1159/000529835