The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies

Shared genetic architecture between gastro-esophageal reflux disease, asthma, and allergic diseases

The aim is to investigate the evidence for shared genetic architecture between each of asthma, allergic rhinitis and eczema with gastro-esophageal reflux disease (GERD). Structural equation models (SEM) and polygenic risk score (PRS) analyses are applied to three Swedish twin cohorts (n = 46,582) and reveal a modest genetic correlation between GERD and asthma of 0.18 and bidirectional PRS and phenotypic associations ranging between OR 1.09-1.14 and no correlations for eczema and allergic rhinitis. Linkage disequilibrium score regression is applied to summary statistics of recently published GERD and asthma/allergic disease genome wide association studies and reveals a genetic correlation of 0.48 for asthma and GERD, and Genomic SEM supports a single latent factor. A gene-/gene-set analysis using MAGMA reveals six pleiotropic genes (two at 12q13.2) associated with asthma and GERD. This study provides evidence that there is a common genetic architecture unique to asthma and GERD that may explain comorbidity and requires further investigation.

Age effects on autism heritability and etiological stability of autistic traits

BACKGROUND

Autism and autistic traits onset in childhood but persist into adulthood. Little is known about how genetic and environmental factors influence autism and autistic traits into adulthood. We aimed to determine age effects on the heritability of clinically diagnosed autism and the etiological stability of autistic traits from childhood to adulthood using twin methods.

METHODS

From 23,849 twin pairs in the Swedish Twin Register born between 1959 and 2010, we identified 485 individuals (1.01%, 31.5% female) with a clinical autism diagnosis. We estimated and compared the relative contribution of genetic, shared, and nonshared environmental influences to autism in childhood and adulthood. We further used multivariate twin analysis with four measurement points among 1,348 twin pairs in the longitudinal Twin Study of Child and Adolescent Development to assess the phenotypic and etiological stability of autistic traits - measured with three scales from the Child Behavior Checklist - from childhood to adulthood.

RESULTS

Autism heritability was comparable from childhood, (96% [95% CI, 76-99%]) to adulthood (87% [67-96%]). Autistic traits were moderately stable (phenotypic correlation = 0.35-0.61) from childhood to adulthood, and their heritability varied between 52 and 71%. We observed stable as well as newly emerging genetic influences on autistic traits from ages 8-9 to 19-20, and unique nonshared environmental influences at each age.

CONCLUSIONS

Genetic factors are important for autism and autistic traits in adulthood and separate genetic studies in adults are warranted.

Migraine heritability and beyond: A scoping review of twin studies

OBJECTIVE

This scoping review aimed to summarize current knowledge from twin studies on migraine. Migraine heritability, genetic correlations with migraine comorbid disorders, and the use of discordant twin pairs in migraine research are described. Further, the review considers the unused potential of twin studies in migraine research and reflects on future directions.

BACKGROUND

Twin studies can be used to understand how heritable and environmental factors influence human traits and disorders. The classical twin design compares the resemblance of a trait in monozygotic twins to that in dizygotic twins. The classical twin design can be extended to estimate the genetic correlation between disorders, model causality, and describe differences within discordant twin pairs.

METHODS

Studies focusing on migraine and using a twin study design were included. The search was performed on the PubMed-MEDLINE database using the search terms "migraine" AND "twin" OR "twins." It was done in May 2023, rerun in November 2023, and managed with the Covidence software.

RESULTS

The search identified 52 twin studies on migraine. In 24 papers, the heritability of migraine was estimated with a classical twin design. Heritability estimates ranged from 0.36 to 0.48 for studies with adults, both men and women, and unspecified migraine. Migraine heritability was predominantly estimated with twin cohorts of North European ancestry, and only two studies examined migraine subtypes. A multilevel classical twin design was used in 11 studies to examine the co-occurrence between migraine and comorbid disorders. The differences within migraine discordant twin pairs were examined in nine studies.

CONCLUSION

The heritability of migraine was estimated with a classical twin design in twin cohorts from seven different countries, with remarkably similar results across studies. Future studies should include migraine subtypes and twin cohorts of non-North European ancestry to better reflect the global population. Beyond heritability estimations, the twin method is a valuable tool for understanding causality and describing differences within discordant twin pairs. Despite more than 80 years of twin studies in migraine research, the twin design has a large unused potential to advance our understanding of migraine.

Polygenic Risk Scores and Twin Concordance for Schizophrenia and Bipolar Disorder

Importance

Schizophrenia and bipolar disorder are highly heritable psychiatric disorders with strong genetic and phenotypic overlap. Twin and molecular methods can be leveraged to predict the shared genetic liability to these disorders.

Objective

To investigate whether twin concordance for psychosis depends on the level of polygenic risk score (PRS) for psychosis and zygosity and compare PRS from cases and controls from several large samples and estimate the twin heritability of psychosis.

Design, Setting, and Participants

In this case-control study, psychosis PRS were generated from a genome-wide association study (GWAS) combining schizophrenia and bipolar disorder into a single psychosis phenotype and compared between cases and controls from the Schizophrenia and Bipolar Twin Study in Sweden (STAR) project. Further tests were conducted to ascertain if twin concordance for psychosis depended on the mean PRS for psychosis. Structural equation modeling was used to estimate heritability. This study constituted an analysis of existing clinical and population datasets with genotype and/or twin data. Included were twins from the STAR cohort and from the Swedish Twin Registry. Data were collected during the 2006 to 2013 period and analyzed from March 2023 to June 2024.

Exposures

PRS for psychosis based on the most recent GWAS of combined schizophrenia/bipolar disorder.

Main Outcomes and Measures

Psychosis case status was assessed by clinical interviews and/or Swedish National Register data.

Results

The final cohort comprised 87 pairs of twins with 1 or both affected and 59 unaffected pairs from the STAR project (for a total of 292 twins) as well as 443 pairs with 1 or both affected and 20 913 unaffected pairs from the Swedish Twin Registry. Among the 292 twins (mean [SD] birth year, 1960 [10.8] years; 158 female [54.1%]; 134 male [45.9%]), 134 were monozygotic twins, and 158 were dyzygotic twins. PRS for psychosis was higher in cases than in controls and associated with twin concordance for psychosis (1-SD increase in PRS, odds ratio [OR], 2.12; 95% CI, 1.23-3.87 on case status in monozygotic twins and OR, 2.74; 95% CI, 1.56-5.30 in dizygotic twins). The association between PRS for psychosis and concordance was not modified by zygosity. The twin heritability was estimated at 0.73 (95% CI, 0.30-1.00), which overlapped with the estimate in the full Swedish Twin Registry (0.69; 95% CI, 0.43-0.85).

Conclusions and Relevance

In this case-control study, using the natural experiment of twins, results suggest that twins with greater inherited liability for psychosis were more likely to have an affected co-twin. Results from twin and molecular designs largely aligned. Even as illness vulnerability is not solely genetic, PRS carried predictive power for psychosis even in a modest sample size.

Possible link between familial susceptibility to cancer and the level of oxidative stress in thyroid cancer patients

BACKGROUND

Hereditary cancer is estimated to account for up to 10% of the worldwide cancer burden; 5% of all thyroid cancers are thought to be genetic. Inheritance of a deleterious mutation in genes associated with a high lifetime risk of developing cancer. Cancer-predisposing genes can promote the initiation and progression of thyroid cancer by enhancing the activation of major signaling pathways through oxidative stress mechanisms.

AIM

Identification of the possible link between familial susceptibility to cancer and the level of oxidative stress in thyroid cancer patients.

METHODS

Patients with thyroid cancer (with and without genetic predisposition) were investigated. Study participants were treated in Limited Liability Company (LLC) "Oncology Scientific Research Center" (Tbilisi, Georgia). The study group was collected between 2020 and 2021. In patients' blood, the thyroid hormones content (free Triiodothyronine (fFT3), free Thyroxine (fFT4), bound Triiodothyronine (FT3), bound Thyroxine (FT4), Thyroid-stimulating hormone (TSH)), and oxidative stress intensity (total activity of non-enzymatic antioxidant system (TAA) and the lipid peroxidation product, malondialdehyde (MDA), content) were investigated.

RESULTS

The difference in free and bound forms of T3 and T4 levels in the blood serum between patients with thyroid cancer (Group 2 and Group 3) and the control group (Group 1) was not statistically significant (F1,2=0.5, p1,2=0.8, F1,3=2.31, p1,3=0.16). In patients with thyroid cancer the TSH level significantly increased compared to the control group (Group 1) (TSH (mean ± Std error): Group 1- 1.21 ± 0.12, Group 2-2.45 ± 0.11 (F1,2=107, p1,2<0.001), Group 3-2.47 ± 0.17 (F1,3=150, p1,3<0.001)) and the MDA levels increased by 4-5 fold. In patients with thyroid cancer from families with cancer aggregation(Group 2), the level of TAA statistically significantly decreased (F1 - 2=200; p1 - 2<0.001), in patients without genetic predisposition to cancer(Group 3), the level of TAA did not change compared to the control (F1 - 3= 2.13; p1 - 3=0.15), CONCLUSIONS: Oxidative stress plays a critical role in tumorigenesis, and antioxidant/oxidant imbalance may contribute to the malignant transformation of normal tissue. In patients with familial susceptibility to cancer mutations of several genes, which are involved in the regulation of oxidative metabolism, may contribute to the disruption of the redox balance, increase the level of oxidative stress, and contribute to the development of thyroid cancer.

Testing Quantitative and Qualitative Sex Effects in a National Swedish Twin-Sibling Study of Posttraumatic Stress Disorder

OBJECTIVE

Twin studies have demonstrated that posttraumatic stress disorder (PTSD) is moderately heritable, and the pattern of findings across studies suggests higher heritability in females compared with males. Formal testing of sex differences has yet to be done in twin studies of PTSD. The authors sought to estimate the genetic and environmental contributions to PTSD, and to formally test for sex differences, in the largest sample to date of both sexes, among twins and siblings.

METHODS

Using the Swedish National Registries, the authors performed structural equation modeling to decompose genetic and environmental variance for PTSD and to formally test for quantitative and qualitative sex differences in twins (16,242 pairs) and in full siblings within 2 years of age of each other (376,093 pairs), using diagnostic codes from medical registries.

RESULTS

The best-fit model suggested that additive genetic and unique environmental effects contributed to PTSD. Evidence for a quantitative sex effect was found, such that heritability was significantly greater in females (35.4%) than males (28.6%). Evidence of a qualitative sex effect was found, such that the genetic correlation was high but less than complete (rg=0.81, 95% CI=0.73-0.89). No evidence of shared environment or special twin environment was found.

CONCLUSIONS

This is the first demonstration of quantitative and qualitative sex effects for PTSD. The results suggest that unique environmental effects, but not the shared environment, contributed to PTSD and that genetic influences for the disorder are stronger in females compared with males. Although the heritability is highly correlated, it is not at unity between the sexes.

Gene-environment interaction in expertise acquisition: Practice effects on musical expertise vary by polygenic scores for cognitive performance

Expert performance is associated with practice, partly because of causal effects of practice on skill (i.e., learning). However, the practice-expertise association is also influenced by a complex interplay between genes and environment including partly overlapping genetic influences. The importance of cognitive ability in the practice-expertise association is less well understood. Therefore, we first examined whether genetic predisposition for cognitive performance, operationalized as a polygenic score, is associated with music practice and expertise. Next, we tested whether there is evidence for gene × environment interaction, i.e., whether effects of practice on expertise differ depending on an individual's genetic predisposition for cognitive performance. Polygenic scores for cognitive performance (PGScp) and multi-trait cognitive performances, including educational attainment and mathematical performances (PGScps) were calculated for approximately 3800 genotyped Swedish individuals with information available on their cumulative amount of music practice, musical achievement, and musical auditory discrimination. We found that higher PGScp and PGScps were associated with higher levels of achievement, musical auditory discrimination, and more practice, although the association with practice weakened when controlling for education. Music practice was linked to both expertise outcomes, and the effect sizes of these associations varied depending on an individual's PGScp and PGScps (with the exception of PGScp for musical auditory discrimination). These results suggest genetic pleiotropy between cognitive performance and musical expertise. Additionally, they reveal the presence of G × E interaction in skill acquisition, as effects of practice on musical expertise are stronger for individuals with a higher genetic predisposition for cognitive performance.

Cohort profile: The Obesity and Disease Development Sweden (ODDS) study, a pooled cohort

PURPOSE

The Obesity and Disease Development Sweden (ODDS) study was designed to create a large cohort to study body mass index (BMI), waist circumference (WC) and changes in weight and WC, in relation to morbidity and mortality.

PARTICIPANTS

ODDS includes 4 295 859 individuals, 2 165 048 men and 2 130 811 women, in Swedish cohorts and national registers with information on weight assessed once (2 555 098 individuals) or more (1 740 761 individuals), in total constituting 7 733 901 weight assessments at the age of 17-103 years in 1963-2020 (recalled weight as of 1911). Information on WC is available in 152 089 men and 212 658 women, out of whom 108 795 have repeated information on WC (in total 512 273 assessments). Information on morbidity and mortality was retrieved from national registers, with follow-up until the end of 2019-2021, varying between the registers.

FINDINGS TO DATE

Among all weight assessments (of which 85% are objectively measured), the median year, age and BMI (IQR) is 1985 (1977-1994) in men and 2001 (1991-2010) in women, age 19 (18-40) years in men and 30 (26-36) years in women and BMI 22.9 (20.9-25.4) kg/m2 in men and 23.2 (21.2-26.1) kg/m2 in women. Normal weight (BMI 18.5-24.9 kg/m2) is present in 67% of assessments in men and 64% in women and obesity (BMI≥30 kg/m2) in 5% of assessments in men and 10% in women. The median (IQR) follow-up time from the first objectively measured or self-reported current weight assessment until emigration, death or end of follow-up is 31.4 (21.8-40.8) years in men and 19.6 (9.3-29.0) years in women. During follow-up, 283 244 men and 123 457 women died.

FUTURE PLANS

The large sample size and long follow-up of the ODDS Study will provide robust results on anthropometric measures in relation to risk of common diseases and causes of deaths, and novel findings in subgroups and rarer outcomes.

The role of familial factors and neuroticism in the association between exposure to offensive behaviors at work and long-term sickness absence due to common mental disorders - a prospective twin study

OBJECTIVES

The aim of this study was to investigate associations between exposure to work-related violence/threats and harassment, and future sickness absence (SA) due to common mental disorders (CMDs), taking familial factors (shared genetics and early-life environment) and neuroticism into account.

METHODS

The study sample included 8795 twin individuals from the Swedish Twin Project of Disability Pension and Sickness Absence (STODS), including survey data from the Study of Twin Adults: Genes and Environment (STAGE). Self-reported work-related violence and/or threats as well as work-related harassment (including bullying) and national register data on SA due to CMDs were analyzed using standard logistic regression, and conditional logistic regression among complete twin pairs discordant on exposures. Individuals were followed for a maximum of 13 years. Interactions between neuroticism and exposures were assessed using both multiplicative and additive interaction analyses.

RESULTS

Exposure to work-related violence/threats was associated with higher odds of SA due to CMDs when adjusting for age, sex, marital status, children, education, type of living area, work characteristics, and symptoms of depression and burnout (OR 2.11, 95% CI 1.52-2.95). Higher odds of SA due to CMDs were also found for exposure to harassment (OR 1.52, 95% CI 1.10-2.11) and a combined indicator of exposure to violence/threats and/or harassment (OR 1.98, 95% CI 1.52-2.59), compared with the unexposed. Analyses of twins discordant on exposure, using the unexposed co-twin as reference, showed reduced ORs. These ORs were still elevated but no longer statistically significant, potentially due to a lack of statistical power. No multiplicative interaction was found between neuroticism and exposure to work-related violence/threats, or harassment. However, a statistically significant additive interaction was found between neuroticism and exposure to violence/threats, indicating higher odds of SA due to CMDs in the group scoring lower on neuroticism.

CONCLUSIONS

Exposure to work-related offensive behaviors was associated with SA due to CMDs. However, the results indicated that these associations may be partly confounded by familial factors. In addition, an interaction between exposure and neuroticism was suggested. Thus, when possible, future studies investigating associations and causality between offensive behaviors at work and mental health-related outcomes, should consider familial factors and neuroticism.

Exploring the genetic etiology across the continuum of the general psychopathology factor: a Swedish population-based family and twin study

Psychiatric comorbidity can be accounted for by a latent general psychopathology factor (p factor), which quantifies the variance that is shared to varying degrees by every dimension of psychopathology. It is unclear whether the entire continuum of the p factor shares the same genetic origin. We investigated whether mild, moderate, and extreme elevations on the p factor shared the same genetic etiology by, first, examining the linearity of the association between p factors across siblings (N = 580,891 pairs). Second, we estimated the group heritability in a twin sample (N = 17,170 pairs), which involves testing whether the same genetic variants influence both extreme and normal variations in the p factor. In both samples, the p factor was based on 10 register-based psychiatric diagnoses. Results showed that the association between siblings' p factors appeared linear, even into the extreme range. Likewise, the twin group heritabilities ranged from 0.42 to 0.45 (95% CI: 0.33-0.57) depending on the thresholds defining the probands (2-3.33 SD beyond the mean; >2 SD beyond the mean; >4.33 SD beyond the mean; and >5.33 SD beyond the mean), and these estimates were highly similar to the estimated individual differences heritability (0.41, 95% CI: 0.39-0.43), indicating that scores above and below these thresholds shared a common genetic origin. Together, these results suggest that the entire continuum of the p factor shares the same genetic origin, with common genetic variants likely playing an important role. This implies, first, genetic risk factors for the aspect that is shared between all forms of psychopathology (i.e., genetic risk factors for the p factor) might be generalizable between population-based cohorts with a higher prevalence of milder cases, and clinical samples with a preponderance of more severe cases. Second, prioritizing low-cost genome-wide association studies capable of identifying common genetic variants, rather than expensive whole genome sequencing that can identify rare variants, may increase the efficiency when studying the genetic architecture of the p factor.

Can flow proneness be protective against mental and cardiovascular health problems? A genetically informed prospective cohort study

Flow is a phenomenon where one experiences optimal challenge, marked by an intense, effortless, and rewarding concentration on a task. Past research shows that flow proneness is associated with good mental and cardiovascular health. However, this research has been primarily cross-sectional, based on self-report data, and has not controlled for potential confounding effects of neuroticism. In a large, longitudinal twin sample (N = 9361), we used nationwide patient registry data to test whether flow proneness predicted registry-based diagnoses of depression, anxiety, schizophrenia, bipolar disorder, stress-related disorders, or cardiovascular diseases. We used survival analyses taking time to diagnosis into account to test if (a) there is a relationship between flow proneness and health diagnoses over time, (b) neuroticism confounds this relationship, and (c) the relationship remains present within discordant monozygotic twin pairs (N = 952), thereby controlling for genetic and shared environmental confounding. Individuals with higher flow proneness had a decreased risk of receiving diagnoses for depression (16%; CI [14%, 18%]), anxiety (16%; CI [13%, 18%]), schizophrenia (15%; CI [4%, 25%]), bipolar (12%; CI [6%, 18%]), stress-related (9%; CI [9%, 12%]), and cardiovascular disorders (4%; CI [1%, 8%]). When controlling for neuroticism, higher flow proneness still decreased the risk of depression (6%; CI [3%, 9%]) and anxiety diagnoses (5%; CI [1%, 8%]). Monozygotic twins who experienced more flow than their co-twin had a lower risk for depression (16%; CI [5%, 26%]) and anxiety (13%; CI [1%, 24%]), though only the association with depression remained significant when also controlling for neuroticism (13%; CI [1%, 24%]). Findings are in line with a causal protective role of flow experiences on depression and potentially anxiety and highlight that neuroticism and familial factors are notable confounding factors in observed associations between flow proneness and health outcomes.

Dementia and mortality in older adults: A twin study

INTRODUCTION

Dementia predicts increased mortality. We used case-control and co-twin control models to investigate genetic and shared environmental influences on this association.

METHODS

Case-control design, including 987 twins with dementia and 2938 age- and sex-matched controls in the Swedish Twin Registry. Co-twin control design, including 90 monozygotic (MZ) and 288 dizygotic (DZ) twin pairs discordant for dementia. To test for genetic and environmental confounding, differences were examined in mortality risk between twins with dementia and their matched or co-twin controls.

RESULTS

Twins with dementia showed greater mortality risk than age- and sex-matched controls (HR = 2.02 [1.86, 2.18]). Mortality risk is significantly elevated but attenuated substantially in discordant twin pairs, for example, comparing MZ twins with dementia to their co-twin controls (HR = 1.48 [1.08, 2.04]).

DISCUSSION

Findings suggest that genetic factors partially confound the association between dementia and mortality and provide an alternative hypothesis to increased mortality due to dementia itself. Highlights We studied dementia and mortality in twin pairs discordant for dementia. People without dementia outlived people with dementia. Identical twins with dementia and their co-twin controls had similar survival time. Findings suggest genotype may explain the link between dementia and mortality.

Associations Between Mid- to Late-Life Body Mass Index and Chronic Disease-Free Survival: A Nationwide Twin Study

BACKGROUND

Some studies have linked late-life overweight to a reduced mortality risk compared to normal body mass index (BMI). However, the impact of late-life overweight and its combination with mid-life BMI status on healthy survival remains unclear. We aimed to investigate whether and to what extent mid- and/or late-life overweight are associated with chronic disease-free survival.

METHODS

Within the Swedish Twin Registry, 11 597 chronic disease-free twins aged 60-79 years at baseline were followed up for 18 years. BMI (kg/m2) was recorded at baseline and 25-35 years before baseline (ie, midlife) and divided as underweight (<20), normal (≥20-25), overweight (≥25-30), and obese (≥30). Incident chronic diseases (cardiovascular diseases, type 2 diabetes, and cancer) and deaths were ascertained via registries. Chronic disease-free survival was defined as years lived until the occurrence of any chronic diseases or death. Data were analyzed using multistate survival analysis.

RESULTS

Of all participants, 5 640 (48.6%) were overweight/obese at baseline. During the follow-up, 8 772 (75.6%) participants developed at least 1 chronic disease or died. Compared to normal BMI, late-life overweight and obesity were associated with 1.1 (95% CI, 0.3, 2.0) and 2.6 (1.6, 3.5) years shorter chronic disease-free survival. Compared to normal BMI through mid- to late life, consistent overweight/obesity and overweight/obesity only in mid-life led to 2.2 (1.0, 3.4) and 2.6 (0.7, 4.4) years shorter disease-free survival, respectively.

CONCLUSIONS

Late-life overweight and obesity may shorten disease-free survival. Further research is needed to determine whether preventing overweight/obesity from mid- to late life might favor longer and healthier survival.

Attention-deficit/hyperactivity disorder symptoms and subsequent cardiometabolic disorders in adults: investigating underlying mechanisms using a longitudinal twin study

BACKGROUND

Emerging research suggests that attention-deficit/hyperactivity disorder (ADHD) increases the risk for cardiovascular (CVDs) and metabolic disorders (i.e., cardiometabolic disorders) in adulthood. Yet, available studies are scarce and have mainly been focused on individuals receiving clinical ADHD diagnoses. We aimed to investigate the prospective associations of ADHD symptoms in young and mid-adulthood with subsequent cardiometabolic disorders and the underlying mechanisms.

METHODS

We studied 10,394 twins from the Swedish Twin Registry (STR), born between 1958 and 1985 without previous medical history of cardiometabolic disorders. They provided self-assessment of ADHD symptoms (score range 0-36) via a validated, DSM-IV-based scale in a web-based questionnaire/telephone interview within the Study of Twin Adults: Genes and Environment (STAGE), in 2005-2006 (aged 19-47 years), and were followed until the end of 2018 (33-59 years) to identify incident clinical diagnoses/medication prescriptions for cardiometabolic disorders acquired from Swedish national registers. We used Cox regression models to investigate the associations between ADHD symptoms score and cardiometabolic outcomes, with and without adjustment for relevant covariates, and a co-twin control design to study familial confounding.

RESULTS

A one-unit increase in the level of ADHD symptoms was associated with a 2% increase in the rate of CVDs (hazard ratio [HR] = 1.02, 95% confidence interval 1.01-1.04) and a 3% increase in the rate of metabolic disorders (HR = 1.03, 1.02-1.05), after adjusting for birth year and sex. The associations were no longer significant after adjusting for educational attainment, lifestyle factors, and comorbid psychiatric disorders. The associations remained significant after adjusting for familial factors shared by dizygotic twin pairs but became nonsignificant after adjusting for factors shared by monozygotic twin pairs. However, the strength of the associations attenuated significantly in monozygotic twins compared to dizygotic twins for CVDs only, suggesting genetic confounding.

CONCLUSIONS

ADHD symptom score is associated with a higher risk for cardiometabolic disorders, which may be explained by lower educational attainment, adverse lifestyle factors, and psychiatric comorbidities. Moreover, the associations appear to be partly confounded by shared genetic factors, especially for CVDs. Further research is needed to investigate the identified associations at the level of individual cardiometabolic disorders and to follow-up participants until a more advanced older age.

Regional differences in annual prevalence of sustainable working life in Swedish twin cohort

The global rise in life expectancy transforms age structure consequently having impact to the sustainability of social protection systems and working life. This descriptive study aimed to illustrate the annual prevalence of sustainable working life across Swedish residential regions, and investigate differences between age groups, sex, or being identical or fraternal twin. The study sample included 81,231 twins with linkage to national register data on sickness absence, disability pension, unemployment, and residential regions. Regions were classified by Swedish municipalities into nine groups. Sustainable working life were then followed in 1998, 2003, 2008, and 2013. Annual prevalence and Generalized Estimating Equation (GEE) with log linear models for interaction test were used. Medium to large size municipalities (15-24%) had higher annual prevalence of sustainable working life than smaller municipalities (1-7%). Young adults in medium to large size municipalities had high annual prevalence of sustainable working life. We found no differences for sexes or being identical or fraternal twin. To conclude, annual prevalence of sustainable working life in 1998, 2003, 2008 and 2013 differed by region being highest in medium to large size municipalities which may have importance for targeting policies, regulations, and practices in a region-specific way. Further studies on residential regions and sustainable working life would be merited to confirm associations and other influential factors.

The Co-Twin Control Design: Implementation and Methodological Considerations

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

Genetic and environmental contributions to individual differences in sustainable working life-A Swedish twin cohort study

Although genetics is known to have a role in sickness absences (SA), disability pensions (DP) and in their mutual associations, the empirical knowledge is scarce on not having these interruptions, i.e., sustainable working life. Hence, we aimed to investigate how genetic and environmental factors affect individual variation in sustainable working life in short-term (two consecutive years) and in long-term (22 years of follow-up) using the classical twin modeling based on different genetic relatedness of mono- and dizygotic twins. The final sample (n = 51 071) included Swedish same-sex twins with known zygosity born between 1930 and 1990 (53% women) with complete national register data of employment, SA, DP, unemployment, old-age pension, emigration, and death. For the short-term sustainable working life, genetic factors explained 36% (95% confidence intervals (CI) 31-41%), environmental factors shared by co-twins such as family background 8% (95% CI 5-14%) and environmental factors unique to each twin individual 56% (95% CI 56-56%) on the individual differences. For the long-term sustainable working life, the largest proportions on individual differences were explained by environmental factors shared by co-twins (46%, 95% CI 44-48%) and unique to each twin individual (37% 95% CI 36-38%) whereas a small proportion was explained by genetic factors (18%, 95%CI 14-22%). To conclude, short-term sustainable working life was explained to a large extent by unique environment and to lesser extent by genetic factors whereas long-term (22 years) sustainable working life had both moderate unique and common environmental effect, and to lower extent genetic effects contributing to individual differences. These findings suggest that sustainable working life have different short- and long-term predictors.

Sickness absence transitions among Swedish twins with back, neck or shoulder pain and common mental disorders applying a multi-state approach

We aimed to investigate transitions to and from sickness absence, or disability pension among individuals with back, neck, or shoulder pain and/or with common mental disorders (CMDs), and the role of familial (genetics and shared environment) influences on the transitions. Swedish twins born 1935-1985 who responded to pain and CMDs survey items (N = 41,516) were followed on average 8.7 years for sickness absence states in national registers. Multi-state Cox regression models were applied for three exposure groups: pain, CMDs, and presence of both, compared to unexposed. Exposure discordant twin pairs, stratified by zygosity, were analysed to assess the role of familial factors. Hazard Ratios (HR) with 95% confidence intervals and transition intensities were calculated. HRs were similar for transitions between states among those with pain or CMDs. The highest HRs were for transitions from entry to sickness absence and sickness absence to disability pension among those with both pain and CMDs (HRs: 1.61 and 1.43, respectively). Higher HRs for dizygotic compared to monozygotic twins for the first transition to sickness absence and for altering back to not being sickness absent indicate familial confounding. Back, neck, or shoulder pain and/or CMDs indicate a higher risk to become sickness absent and for repeated sickness absence episodes over time compared to unaffected.

Work incapacity and psychiatric patient care following attempted suicide - a cohort study of 65 097 Swedish twins

BACKGROUND

Research is scarce on the role of familial factors and previous psychiatric care on the association between suicide attempt and future work incapacity as well as deterioration in mental health. We aimed to investigate the associations between suicide attempt and sickness absence, disability pension and psychiatric patient care and to study the influence of previous psychiatric care and familial factors (genetics and shared environment) on the associations.

METHODS

The study included 65 097 twins living in Sweden on 31st of December 2006, aged 19-60 years. The twins were followed 2007-2013 regarding sickness absence, disability pension, inpatient care or specialized outpatient care for a mental diagnosis. Cox regression models were performed for the whole sample, and conditional models for discordant twin pairs. The analyses were also stratified by psychiatric care before 2007.

RESULTS

We found that suicide attempt predicted sickness absence, disability pension, and future mental diagnosis among the whole sample. The discordant twin pair analyses showed that the association between suicide attempt and sickness absence or disability pension was influenced by familial factors. Stratified analyses of individuals with or without psychiatric care before 2007 showed that previous psychiatric care had some impact on the associations.

CONCLUSIONS

A suicide attempt is a risk factor for work incapacity and psychiatric patient care. Familial factors and previous psychiatric care play a role in the associations between attempting suicide and work incapacity as well as psychiatric patient care. These factors are important when developing measures preventing work incapacity among those with a suicide attempt.

Longitudinal analyses indicate bidirectional associations between loneliness and health

OBJECTIVES

To evaluate temporal dynamics between loneliness and both objective and subjective health (i.e. functional impairment and self-rated health) in mid- to late-adulthood.

METHOD

We applied bivariate dual-change-score models to longitudinal data from 3 Swedish twin studies (N = 1,939) to explore dynamic associations between loneliness and health across 3 age ranges (50-69, 70-81, and 82+ years) to investigate whether associations between loneliness and health change with age due to increasing incidence of chronic health conditions and bereavement.

RESULTS

Results showed bidirectional associations between loneliness and both objective and subjective health, with adverse impacts of loneliness observed on subsequent subjective and objective health beginning at age 70. Associations between health and subsequent loneliness were observed after age 82 and varied for subjective and objective health, with subjective health associated with less loneliness and objective health associated with greater loneliness.

CONCLUSIONS

Our results indicate dynamic associations between loneliness and health with age in mid- to late-adulthood, with earlier impacts of loneliness on health and later impacts of health on loneliness that vary for objective and subjective measures of health. These findings suggest impacts of health on loneliness may arise later in life when worsening health or mobility interfere with social interaction.

Influences of genetically predicted and attained education on geographic mobility and their association with mortality

INTRODUCTION

Both educational attainment and genetic propensity to education (PGSEdu) have been associated with geographic mobility. Socioeconomic conditions are, in turn, associated with individuals' health. Geographic mobility could therefore lead to better health for some since it could provide better opportunities, like education. Our aim was to study how attained education and genetic predisposition for higher education are related to geographic mobility, and how they affect the association between geographic mobility and mortality.

METHODS

We used data from the Swedish Twin Registry (twins born 1926-1955; n = 14,211) in logistic regression models to test if attained education and PGSEdu predicted geographic mobility. Cox regression models were then performed to test if geographic mobility, attained education, and PGSEdu were associated with mortality.

RESULTS

The results show that both attained education and PGSEdu predicted geographic mobility, in both independent and joint effect models, with higher education associated with higher mobility. Geographic mobility was associated with lower mortality in the independent effect model, but joint effect models showed that this association was completely explained by attained education.

CONCLUSIONS

To conclude, both attained education and PGSEdu were associated with geographic mobility. Moreover, attained education explained the relationship between geographic mobility and mortality.

Etiology of the Broad Avoidant Restrictive Food Intake Disorder Phenotype in Swedish Twins Aged 6 to 12 Years

Importance

Avoidant restrictive food intake disorder (ARFID) is characterized by an extremely limited range and/or amount of food eaten, resulting in the persistent failure to meet nutritional and/or energy needs. Its etiology is poorly understood, and knowledge of genetic and environmental contributions to ARFID is needed to guide future research.

Objective

To estimate the extent to which genetic and environmental factors contribute to the liability to the broad ARFID phenotype.

Design, Setting, and Participants

This nationwide Swedish twin study includes 16 951 twin pairs born between 1992 and 2010 whose parents participated in the Child and Adolescent Twin Study in Sweden (CATSS) at twin age 9 or 12 years. CATSS was linked to the National Patient Register (NPR) and the Prescribed Drug Register (PDR). Data were collected from July 2004 to April 2020, and data were analyzed from October 2021 to October 2022.

Main Outcomes and Measures

From CATSS, NPR, and PDR, all parent reports, diagnoses, procedures, and prescribed drugs that were relevant to the DSM-5 ARFID criteria were extracted when twin pairs were aged 6 to 12 years and integrated into a composite measure for the ARFID phenotype (ie, avoidant/restrictive eating with clinically significant impact, such as low weight or nutritional deficiency, and with fear of weight gain as an exclusion). In sensitivity analyses, autism and medical conditions that could account for the eating disturbance were controlled for. Univariate liability threshold models were fitted to estimate the relative contribution of genetic and environmental variation to the liability to the ARFID phenotype.

Results

Of 33 902 included children, 17 151 (50.6%) were male. A total of 682 children (2.0%) with the ARFID phenotype were identified. The heritability of ARFID was 0.79 (95% CI, 0.70-0.85), with significant contributions from nonshared environmental factors (0.21; 95% CI, 0.15-0.30). Heritability was very similar when excluding children with autism (0.77; 95% CI, 0.67-0.84) or medical illnesses that could account for the eating disturbance (0.79; 95% CI, 0.70-0.86).

Conclusions and Relevance

Prevalence and sex distribution of the broad ARFID phenotype were similar to previous studies, supporting the use of existing epidemiological data to identify children with ARFID. This study of the estimated genetic and environmental etiology of ARFID suggests that ARFID is highly heritable, encouraging future twin and molecular genetic studies.

Does lower educational attainment increase the risk of osteoarthritis surgery? a Swedish twin study

BACKGROUND

Previous studies have reported an inverse association between educational attainment and different osteoarthritis (OA) outcomes. However, none of the previous studies have accounted for potential confounding by early-life environment and genetics. Thus, we aimed to examine the association between educational attainment and knee and hip OA surgery using twin data.

METHODS

From the Swedish Twin Registry (STR), we identified dizygotic (DZ) and monozygotic (MZ) twins. All twins in the STR aged 35 to 64 years were followed from January the 1^st 1987 or the date they turned 35 years until OA surgery, relocation outside Sweden, death or the end of 2016 (18,784 DZ and 8,657 MZ complete twin pairs). Associations between educational attainment and knee and hip OA surgery were estimated in models matched on twin pairs, using Weibull within-between (WB) shared frailty model.

RESULTS

For knee OA surgery, the analysis matched on MZ twins yielded a within-estimate hazard ratio (HR) per 3 years of education, of 1.06 (95% CI: 0.81, 1.32), suggesting no association between the outcome and the individual´s education. Rather, there seemed to be a so called familial effect of education, with a between-pair estimate of HR = 0.71 (95% CI: 0.41, 1.01). For hip OA surgery, the within- and between-pair estimates for MZ twins were 0.92 (95% CI: 0.69, 1.14) and 1.15 (95% CI: 0.87, 1.42), respectively.

CONCLUSIONS

Our results suggest that the inverse associations between education and knee/hip OA surgery observed in cohort studies are potentially confounded by unobserved familial factors like genetics and/or early life exposures.

A comprehensive investigation into the genetic relationship between music engagement and mental health

While music engagement is often regarded as beneficial for mental health, some studies report higher risk for depression and anxiety among musicians. This study investigates whether shared underlying genetic influences (genetic pleiotropy) or gene-environment interaction could be at play in the music-mental health association using measured genotypes. In 5,648 Swedish twins with information on music and sport engagement, creative achievements, self-reported mental health and psychiatric diagnoses based on nationwide patient registries, we derived polygenic scores for major depression, bipolar disorder, schizophrenia, neuroticism, sensitivity to environmental stress, depressive symptoms and general musicality. In line with phenotypic associations, individuals with higher polygenic scores for major depression and bipolar disorder were more likely to play music, practice more music and reach higher levels of general artistic achievements, while a higher genetic propensity for general musicality was marginally associated with a higher risk for a depression diagnosis. Importantly, polygenic scores for major depression and bipolar remained associated with music engagement when excluding individuals who experienced psychiatric symptoms, just as a genetic propensity for general musicality predicted a depression diagnosis regardless of whether and how much individuals played music. In addition, we found no evidence for gene-environment interaction: the phenotypic association between music engagement and mental health outcomes did not differ for individuals with different genetic vulnerability for mental health problems. Altogether, our findings suggest that mental health problems observed in musically active individuals are partly explained by a pre-existing genetic risk for depression and bipolar disorder and likely reflect horizontal pleiotropy (when one gene influences multiple traits), rather than causal influences of mental health on music engagement, or vice versa (referred to as vertical pleiotropy).

Trajectories of sustainable working life in nine Swedish residential regions: A longitudinal twin cohort study

OBJECTIVE

To investigate trajectories of sustainable working life (SWL, ie, no interruptions or transitions in working life due to sickness absence (SA), disability pension (DP), or unemployment) in Swedish residential regions using a population-based twin cohort, while assessing sociodemographics and twin pair similarity.

METHODS

Sample of 60 998 twins born in 1925-1958. SWL was assessed through main labor market status in each year in 1998-2016 based on > 180 days with SA/DP, > 180 days with unemployment, or >half of yearly income from old-age pension for not in SWL, and employment (in paid work and did not fulfill the criteria SA/DP, unemployment, or old-age pension) for SWL. Residential regions were classified into nine groups based on Swedish municipalities. Group-based trajectory models and multinomial logistic regression were applied separately for all regions.

RESULTS

In all regions, the largest trajectory group was sustainable working life. Three to four trajectory groups developed toward unsustainable working life with different exit points from sustainable working life. A small proportion were grouped with partial stable or increase in sustainable working life. Increased age, being a woman, <12 years of education, and history of unstable working life increased, and being married and twin pair similarity decreased the likelihood of belonging to trajectories toward unsustainable working life.

CONCLUSIONS

In all regions, most of the individuals followed a sustainable working life trajectory. A reasonable proportion of individuals followed trajectories developing toward unsustainable working life. The influence of sociodemographic and familial factors on trajectory groups was similar in all regions.

Bibliometric Analysis of Research Themes and Trends of the Co-Occurrence of Autism and ADHD

Background

In recent years, there has been a growing body of research suggesting that ASD and ADHD are two disorders that often co-exist. Despite the rapid development of research, little is known about their etiology, diagnostic markers, and interventions, which has led us to review and summarise the development of the field in the hope that this will provide an opportunity to look for future directions.

Methods

A bibliometric approach was used to analyse papers in the field of ASD co-morbidities in ADHD on Web of Science from 1991-2022, using CiteSpace and VOSview to map the country/institution, journal, author, co-citation, and keyword networks in the field and to visualise the results.

Results

A total of 3284 papers were included, showing an increasing trend in terms of posting trends. Research on co-morbidities of ASD has proven to be mainly focused on universities. The USA (1662) published the most relevant literature in this area, followed by the UK (651) and Sweden (388). Lichtenstein P is the most published author (84), and research into the pathogenesis of ASD co-occurring ADHD and related clinical diagnostics is currently at the forefront of the field.

Conclusion

This analysis identifies the most influential institutions and countries, cited journals, and authors in the field of ASD co-morbid ADHD research. The future direction of ASD co-occurring ADHD should be based on improving case identification, discovering the etiological and diagnostic markers of ASD and ADHD, and finding more effective clinical interventions.

Rare tandem repeat expansions associate with genes involved in synaptic and neuronal signaling functions in schizophrenia

Tandem repeat expansions (TREs) are associated with over 60 monogenic disorders and have recently been implicated in complex disorders such as cancer and autism spectrum disorder. The role of TREs in schizophrenia is now emerging. In this study, we have performed a genome-wide investigation of TREs in schizophrenia. Using genome sequence data from 1154 Swedish schizophrenia cases and 934 ancestry-matched population controls, we have detected genome-wide rare (<0.1% population frequency) TREs that have motifs with a length of 2-20 base pairs. We find that the proportion of individuals carrying rare TREs is significantly higher in the schizophrenia group. There is a significantly higher burden of rare TREs in schizophrenia cases than in controls in genic regions, particularly in postsynaptic genes, in genes overlapping brain expression quantitative trait loci, and in brain-expressed genes that are differentially expressed between schizophrenia cases and controls. We demonstrate that TRE-associated genes are more constrained and primarily impact synaptic and neuronal signaling functions. These results have been replicated in an independent Canadian sample that consisted of 252 schizophrenia cases of European ancestry and 222 ancestry-matched controls. Our results support the involvement of rare TREs in schizophrenia etiology.

Association of life-course traumatic brain injury with dementia risk: A nationwide twin study

INTRODUCTION

The impact of life-course traumatic brain injury (TBI) on dementia is unclear.

METHODS

Within the Swedish Twin Registry (STR), 35,312 dementia-free twins were followed for up to 18 years. TBI history was identified via medical records. Data were analyzed using generalized estimating equation (GEE) and conditional logistic regression.

RESULTS

In multi-adjusted GEE models, the odds ratio (OR, 95% confidence interval [CI]) of dementia was 1.27 (1.03-1.57) for TBI at any age, 1.55 (1.04-2.31) for TBI at 50 to 59 years, and 1.67 (1.12-2.49) for TBI at 60 to 69 years. Cardiometabolic diseases (CMDs) increased dementia risk associated with TBI at age 50 to 69 years. The ORs in GEE and conditional logistic regression did not differ significantly (P = .37).

DISCUSSION

TBI, especially between ages 50 and 69 years, is associated with an increased risk of dementia, and this is exacerbated among people with CMDs. Genetic and early-life environmental factors may not account for the TBI-dementia association.

Overall assessment for selected markers from high-throughput data

Reproducibility, a hallmark of science, is typically assessed in validation studies. We focus on high-throughput studies where a large number of biomarkers is measured in a training study, but only a subset of the most significant findings is selected and re-tested in a validation study. Our aim is to get the statistical measures of overall assessment for the selected markers, by integrating the information in both the training and validation studies. Naive statistical measures, such as the combined P $$ P $$ -value by conventional meta-analysis, that ignore the non-random selection are clearly biased, producing over-optimistic significance. We use the false-discovery rate (FDR) concept to develop a selection-adjusted FDR (sFDR) as an overall assessment measure. We describe the link between the overall assessment and other concepts such as replicability and meta-analysis. Some simulation studies and two real metabolomic datasets are considered to illustrate the application of sFDR in high-throughput data analyses.

Cardiometabolic multimorbidity and incident dementia: the Swedish twin registry

AIMS

Cardiometabolic diseases (CMDs), including diabetes, heart disease, and stroke, are established risk factors for dementia, but their combined impact has been investigated only recently. This study aimed to examine the association between mid- and late-life cardiometabolic multimorbidity and dementia and explore the role of genetic background in this association.

METHODS AND RESULTS

Within the Swedish Twin Registry, 17 913 dementia-free individuals aged ≥60 were followed for 18 years. CMDs [including age of onset in mid (60) or late (≥60) life] and dementia were ascertained from medical records. Cardiometabolic multimorbidity was defined as having ≥2 CMDs. Cox regression was used to estimate the CMD-dementia association in (i) a classical cohort study design and (ii) a co-twin study design involving 356 monozygotic and dizygotic pairs. By comparing the strength of the association in the two designs, the contribution of genetic background was estimated. At baseline, 3,312 (18.5%) participants had 1 CMD and 839 (4.7%) had ≥2 CMDs. Over the follow-up period, 3,020 participants developed dementia. In the classic cohort design, the hazard ratio (95% confidence interval) of dementia was 1.42 (1.27-1.58) for 1 CMD and 2.10 (1.73-2.57) for ≥2 CMDs. Dementia risk was stronger with mid-life as opposed to late-life CMDs. In the co-twin design, the CMD-dementia association was attenuated among monozygotic [0.99 (0.50-1.98)] but not dizygotic [1.55 (1.15-2.09)] twins, suggesting that the association was in part due to genetic factors common to both CMDs and dementia.

CONCLUSION

Cardiometabolic multimorbidity, particularly in mid-life, is associated with an increased risk of dementia. Genetic background may underpin this association.

Injurious falls before, during and after dementia diagnosis: a population-based study

BACKGROUND

the timing of incident injurious falls at different stages of dementia diagnosis is unclear.

OBJECTIVES

to identify when the occurrence of injurious falls begins to increase among individuals who are going to develop dementia, to explore the time point at which people living with dementia are at highest risk of injurious falls and to ascertain differences in fall-related factors pre- and post-dementia diagnosis.

DESIGN

this study included 2,707 participants with incident dementia and 2,707 1:1 matched (i.e. same birth year and sex) controls without dementia.

METHODS

dementia diagnosis and date of onset were identified from the National Patient Registry (NPR) and the Swedish Cause of Death Register following international criteria. Information on injurious falls and history of chronic disease was obtained from the NPR. Data were analysed using conditional Poisson regression and generalized estimating equation models.

RESULTS

compared with controls, the incidence of injurious falls among participants with dementia started to increase beginning 4 years pre-diagnosis (incidence rate ratio [IRR] 1.70, 95% confidence interval [CI] 1.30-2.22), reaching a peak (IRR 3.73, 95% CI 3.16-4.41) in the year of dementia diagnosis. Heavy drinking, physically active and cardiometabolic diseases (CMDs) were associated with incident falls among those with dementia.

CONCLUSION

people with dementia have a higher incidence of injurious falls beginning 4 years leading up to diagnosis and peaking during the year of diagnosis. Older age, female, heavy drinking, physically active and CMDs may predict injurious falls among people with dementia.

Elemental Dynamics in Hair Accurately Predict Future Autism Spectrum Disorder Diagnosis: An International Multi-Center Study

Autism spectrum disorder (ASD) is a neurodevelopmental condition diagnosed in approximately 2% of children. Reliance on the emergence of clinically observable behavioral patterns only delays the mean age of diagnosis to approximately 4 years. However, neural pathways critical to language and social functions develop during infancy, and current diagnostic protocols miss the age when therapy would be most effective. We developed non-invasive ASD biomarkers using mass spectrometry analyses of elemental metabolism in single hair strands, coupled with machine learning. We undertook a national prospective study in Japan, where hair samples were collected at 1 month and clinical diagnosis was undertaken at 4 years. Next, we analyzed a national sample of Swedish twins and, in our third study, participants from a specialist ASD center in the US. In a blinded analysis, a predictive algorithm detected ASD risk as early as 1 month with 96.4% sensitivity, 75.4% specificity, and 81.4% accuracy (n = 486; 175 cases). These findings emphasize that the dynamics in elemental metabolism are systemically dysregulated in autism, and these signatures can be detected and leveraged in hair samples to predict the emergence of ASD as early as 1 month of age.

Is the Pandemic Wearing Us Out? A Cross-Sectional Study of the Prevalence of Fatigue in Adult Twins without Previous SARS-CoV-2 Infection

During the pandemic, mental health was not only impaired in people after a SARS-CoV-2 infection, but also in people without previous infection. This is the first study on twins without prior SARS-CoV-2 infection to estimate the influence of genetic components and shared as well as individual environments on pandemic-associated fatigue. The study sample included 55 monozygotic and 45 dizygotic twin pairs. A total of 34.5% reported an increase in fatigue since the pandemic. A significant correlation was shown between the responses within monozygotic (χ2[1] = 11.14, p = 0.001) and dizygotic pairs (χ2[1] = 18.72, p < 0.001). In all pandemic-associated fatigue dimensions, individual environment (ranging from e2 = 0.64 to e2 = 0.84) and heritability (ranging from h2 = 0.32 to h2 = 1.04) seem to have the highest impact. The number of comorbidities significantly correlated with physical fatigue (Spearman’s ρ = 0.232, p < 0.001) and psychological impairment due to pandemic measures with the total fatigue score (Spearman’s ρ = 0.243, p < 0.001). However, calculated ANCOVAs with these significant correlations as covariates showed no significant influence on the mean values of the respective fatigue dimensions. Susceptibility to pandemic-associated fatigue may be genetically and environmentally determined, while intensity is also influenced by individual components. The prevalence of fatigue is high even in individuals without prior SARS-CoV-2 infection. Future mental health prevention and intervention programs should be implemented to alleviate the impact of the pandemic on the global population.

Association of life-course reproductive duration with mortality: a population-based twin cohort study

BACKGROUND

Although age at menopause has been linked to mortality, the association between the entire reproductive lifespan and mortality remains unclear.

OBJECTIVE

This study aimed to examine to what extent life-course reproductive duration is associated with all-cause mortality and explore the role of a healthy lifestyle and familial background in such an association.

STUDY DESIGN

A total of 11,669 women (mean age, 63.54 years) from the Swedish Twin Registry were followed for up to 19 years. Information on reproductive duration (the interval between ages at menarche and menopause) and lifestyle factors (including smoking, alcohol consumption, and physical activity; divided into unfavorable/intermediate/favorable) was collected on the basis of a structured questionnaire. Survival status was obtained from the Sweden Cause of Death Register. The data were analyzed using generalized estimating equation models, Laplace regression, and conditional logistic regression.

RESULTS

In the generalized estimating equation model, compared with those with ≤34 reproductive years, the odds ratio (95% confidence interval) of all-cause mortality was 0.79 (0.68-0.90) for those with ≥40 reproductive years, which prolonged survival time by 0.84 (0.24-1.43) years. Women with ≥40 reproductive years plus a favorable lifestyle (odds ratio, 0.28; 95% confidence interval, 0.23-0.35) were at a lower risk of all-cause mortality than those with <40 reproductive years plus an unfavorable lifestyle. An additive interaction between ≥40 reproductive years and a favorable lifestyle on all-cause mortality was observed (attributable proportion, 0.584; 95% confidence interval, 0.016-1.151). The odds ratios in conditional logistic regression and generalized estimating equation models did not differ significantly (P=.67).

CONCLUSION

A longer reproductive lifespan is associated with reduced all-cause mortality and prolongs survival by 0.84 years. A favorable lifestyle may amplify the beneficial effect of longer reproductive lifespan on mortality. Familial background does not account for the observed association.

Association of depression with mortality in nationwide twins: The mediating role of dementia

BACKGROUND

The differential impact of depression across different periods in life on mortality remains inconclusive. We aimed to examine the association of depression that occurs at different age with all-cause mortality, and to explore the roles of dementia, as well as genetic and early-life environmental factors, in this association.

METHODS

From the Swedish Twin Registry, 44,919 twin individuals were followed for up to 18 years. Depression was ascertained using the National Patient Registry and categorized as early-life (<45 years), midlife (45-64 years), and late-life (≥65 years) depression according to the age of the first diagnosis. Deaths were identified through the Cause of Death Register. Generalized estimating equation, generalized structural equation, and conditional logistic regression were used for unmatched, mediation, and co-twin matched analyses, respectively.

RESULTS

In unmatched analyses, the multivariate-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) of mortality were 1.71 (1.46-2.00) for depression at any age, 1.72 (1.36-2.17) for early-life, 1.51 (1.19-1.90) for midlife, and 4.10 (2.02-8.34) for late-life depression. Mortality was significantly higher in individuals with late-life depression than those with earlier-life depression (p < 0.05). The mediation analysis showed that 59.83% of the depression-mortality association was mediated by dementia. No significant difference in ORs between the unmatched and co-twin matched analyses was observed (p = 0.09).

CONCLUSIONS

Depression is associated with an increased risk of all-cause mortality, and dementia mediates approximately 60% of the impact of depression on mortality in late life. Genetic and early-life environmental factors may not play a significant role in the depression-mortality association.

Bidirectional associations between body mass and bodily pain among middle-aged and older adults

ABSTRACT

Higher body mass and obesity are associated with bodily pain, and rates of chronic pain increase among older adults. Most past studies are cross-sectional, precluding determination of the temporal relationship between body mass and pain. A longitudinal study of body mass and pain among middle-aged adults found that higher body mass index (BMI) led to greater lower back pain. No longitudinal study of BMI and pain has been conducted among adults older than 70 years. This study used dual change score models to determine the directional relationship between BMI and bodily pain in a sample of middle-aged and older adults. Participants (n = 1889) from the Swedish Twin Registry (baseline age range 40-93 years) completed at least 1 nurse assessment of BMI and self-report ratings of pain interference and joint pain. Pain interference was not associated with BMI, but joint pain was analyzed in univariate and bivariate models, with dual change score models modeling the relationship of BMI and joint pain across age, both independently and as part of bivariate relationships. The results indicated a reciprocal relationship between BMI and joint pain, but joint pain generally led to changes in BMI. In addition, the relationship changed with age, until approximately age 80 years, increasing joint pain contributed to higher BMI, but after that time increasing joint pain contributed to lower BMI. In addition, sex differences in the relationship between BMI and pain appeared after age 70 years. Thus, joint pain contributes to changes in BMI among middle-aged and older adults, but the relationship may change by age and sex.

Abnormal cerebrospinal fluid levels of amyloid and tau are associated with cognitive decline over time in cognitively normal older adults: A monozygotic twin study

Introduction

The contribution of genetic and environmental factors to the relation between cerebrospinal fluid (CSF) biomarkers and cognitive decline in preclinical Alzheimer's disease remains unclear. We studied this in initially cognitively normal monozygotic twins.

Methods

We included 122 cognitively normal monozygotic twins (51 pairs) with a follow-up of 4.3 ± 0.4 years. We first tested associations of baseline CSF Aβ1-42/1-40 ratio, total tau (t-tau), and 181-phosphorylated-tau (p-tau) status with subsequent cognitive decline using linear mixed models, and then performed twin specific analyses.

Results

Baseline abnormal amyloid-β and tau CSF markers predicted steeper decline on memory (p ≤ .003) and language (p ≤ 0.04). Amyloid-β and p-tau markers in one twin predicted decline in memory in the co-twin and tau markers in one twin predicted decline in language in the co-twin (r range -0.26,0.39; p's ≤ .02).

Discussion

These results suggest that memory and language decline are early features of AD that are in part determined by the same genetic factors that influence amyloid-β and tau regulation.

Using a polygenic score in a family design to understand genetic influences on musicality

To further our understanding of the genetics of musicality, we explored associations between a polygenic score for self-reported beat synchronization ability (PGS_rhythm) and objectively measured rhythm discrimination, as well as other validated music skills and music-related traits. Using family data, we were able to further explore potential pathways of direct genetic, indirect genetic (through passive gene–environment correlation) and confounding effects (such as population structure and assortative mating). In 5648 Swedish twins, we found PGS_rhythm to predict not only rhythm discrimination, but also melody and pitch discrimination (betas between 0.11 and 0.16, p < 0.001), as well as other music-related outcomes (p < 0.05). In contrast, PGS_rhythm was not associated with control phenotypes not directly related to music. Associations did not deteriorate within families (N = 243), implying that indirect genetic or confounding effects did not inflate PGS_rhythm effects. A correlation (r = 0.05, p < 0.001) between musical enrichment of the family childhood environment and individuals' PGS_rhythm, suggests gene–environment correlation. We conclude that the PGS_rhythm captures individuals' general genetic musical propensity, affecting musical behavior more likely direct than through indirect or confounding effects.

Investigating the Relationship Between Childhood Music Practice and Pitch-Naming Ability in Professional Musicians and a Population-Based Twin Sample

The relationship between pitch-naming ability and childhood onset of music training is well established and thought to reflect both genetic predisposition and music training during a critical period. However, the importance of the amount of practice during this period has not been investigated. In a population sample of twins (N = 1447, 39% male, 367 complete twin pairs) and a sample of 290 professional musicians (51% male), we investigated the role of genes, age of onset of playing music and accumulated childhood practice on pitch-naming ability. A significant correlation between pitch-naming scores for monozygotic (r = .27, p < .001) but not dizygotic twin pairs (r = -.04, p = .63) supported the role of genetic factors. In professional musicians, the amount of practice accumulated between ages 6 and 11 predicted pitch-naming accuracy (p = .025). In twins, age of onset was no longer a significant predictor once practice was considered. Combined, these findings are in line with the notion that pitch-naming ability is associated with both genetic factors and amount of early practice, rather than just age of onset per se. This may reflect a dose-response relation between practice and pitch-naming ability in genetically predisposed individuals. Alternatively, children who excel at pitch-naming may have an increased tendency to practice.

Association of Sleep Duration, Napping, and Sleep Patterns With Risk of Cardiovascular Diseases: A Nationwide Twin Study

Background

Although sleep disorders have been linked to cardiovascular diseases (CVDs), the association between sleep characteristics and CVDs remains inconclusive. We aimed to examine the association of nighttime sleep duration, daytime napping, and sleep patterns with CVDs and explore whether genetic and early‐life environmental factors account for this association.

Methods and Results

In the Swedish Twin Registry, 12 268 CVD‐free twin individuals (mean age=70.3 years) at baseline were followed up to 18 years to detect incident CVDs. Sleep duration, napping, and sleep patterns (assessed by sleep duration, chronotype, insomnia, snoring, and daytime sleepiness) were self‐reported at baseline. CVDs were ascertained through the Swedish National Patient Registry and the Cause of Death Register. Data were analyzed using a Cox model. In the multiadjusted Cox model, compared with 7 to 9 hours/night, the hazard ratios (HRs) of CVDs were 1.14 (95% CI, 1.01–1.28) for <7 hours/night and 1.10 (95% CI, 1.00–1.21) for ≥10 hours/night, respectively. Compared with no napping, napping 1 to 30 minutes (HR, 1.11 [95% CI, 1.03–1.18]) and >30 minutes (HR, 1.23 [95% CI, 1.14–1.33]) were related to CVDs. Furthermore, a poor sleep pattern was associated with CVDs (HR, 1.22 [95% CI, 1.05–1.41]). The co‐twin matched control analyses showed similar results as the unmatched analyses, and there was no significant interaction between sleep characteristics and zygosity (P values >0.05).

Conclusions

Short or long sleep (<7 or ≥10 hours/night), napping, and poor sleep patterns are associated with an increased CVD risk. Genetic and early‐life environmental factors may not account for the sleep–CVD association.

Psychosocial Working Conditions and Subsequent Sickness Absence-Effects of Pain and Common Mental Disorders in a Population-Based Swedish Twin Sample

OBJECTIVE

To investigate pain and/or common mental disorders (CMDs) in the associations between psychosocial working conditions and sickness absence (SA) while controlling familial confounding.

METHODS

Prospective Prospective twin cohort study included survey data for pain and CMD, register data for SA and psychosocial working conditions. The follow-up from 2005 to 2016 of 28,916 twin individuals for first incident SA spell measured as the main International Classification of Diseases version 10 (ICD-10) diagnosis groups (F00-F99, I00-I99, and M00-M99), or the duration. We used regression models to obtain odds ratio (OR), incidence rate ratio (IRR), or relative risk ratio (RRR) with 95% confidence intervals (CI).

RESULTS

The covariate adjusted models of 9156 SA spells indicated almost no statistically significant associations between psychosocial working conditions and SA.

CONCLUSIONS

Psychosocial working conditions were not associated with SA while familial confounding could not be ruled out.

Detecting the unknown in a sea of knowns: Health surveillance, knowledge infrastructures, and the quest for classification egress

The sociological study of knowledge infrastructures and classification has traditionally focused on the politics and practices of classifying things or people. However, actors' work to escape dominant infrastructures and pre-established classification systems has received little attention. In response to this, this article argues that it is crucial to analyze, not only the practices and politics of classification, but also actors' work to escape dominant classification systems. The article has two aims: First, to make a theoretical contribution to the study of classification by proposing to pay analytical attention to practices of escaping classification, what the article dubs classification egress. This concept directs our attention not only to the practices and politics of classifying things, but also to how actors work to escape or resist classification systems in practice. Second, the article aims to increase our understanding of the history of quantified and statistical health surveillance. In this, the article investigates how actors in health surveillance assembled a knowledge infrastructure for surveilling, quantifying, and detecting unknown patterns of congenital malformations in the wake of the thalidomide disaster in the early 1960s. The empirical account centers on the actors' work to detect congenital malformations and escape the dominant nosological classification of diseases, the International Classification of Diseases (ICD), by replacing it with a procedural standard for reporting of symptoms. Thus, the article investigates how actors deal with the tension between the-already-known-and-classified and the unknown-unclassified-phenomenon in health surveillance practice.

The role of ADHD genetic risk in mid-to-late life somatic health conditions

Growing evidence suggests that ADHD, an early onset neurodevelopmental disorder, is associated with poor somatic health in adulthood. However, the mechanisms underlying these associations are poorly understood. Here, we tested whether ADHD polygenic risk scores (PRS) are associated with mid-to-late life somatic health in a general population sample. Furthermore, we explored whether potential associations were moderated and mediated by life-course risk factors. We derived ADHD-PRS in 10,645 Swedish twins born between 1911 and 1958. Sixteen cardiometabolic, autoimmune/inflammatory, and neurological health conditions were evaluated using self-report (age range at measure 42-88 years) and clinical diagnoses defined by International Classification of Diseases codes in national registers. We estimated associations of ADHD-PRS with somatic outcomes using generalized estimating equations, and tested moderation and mediation of these associations by four life-course risk factors (education level, body mass index [BMI], tobacco use, alcohol misuse). Results showed that higher ADHD-PRS were associated with increased risk of seven somatic outcomes (heart failure, cerebro- and peripheral vascular disease, obesity, type 1 diabetes, rheumatoid arthritis, and migraine) with odds ratios ranging 1.07 to 1.20. We observed significant mediation effects by education, BMI, tobacco use, and alcohol misuse, primarily for associations of ADHD-PRS with cardiometabolic outcomes. No moderation effects survived multiple testing correction. Our findings suggests that higher ADHD genetic liability confers a modest risk increase for several somatic health problems in mid-to-late life, particularly in the cardiometabolic domain. These associations were observable in the general population, even in the absence of medical treatment for ADHD, and appear to be in part mediated by life-course risk factors.

Cancer in twin pairs discordant for smoking: The Nordic Twin Study of Cancer

The discordant twin pair study design is powerful to control for familial confounding. We employed this approach to investigate the associations of smoking with several cancers. The NorTwinCan study combines data from the Danish, Finnish, Norwegian and Swedish twin and cancer registries. Follow‐up started when smoking status was determined and ended at cancer diagnosis confirmed by information in the cancer registry, death or end of follow‐up. We classified the participants as never (n = 59 093), former (n = 21 168) or current (n = 47 314) smokers. We pooled data from twin pairs where one co‐twin was diagnosed with any of the following tobacco‐related cancers: esophagus, kidney, larynx, liver, oral cavity, pancreas, pharynx or urinary bladder, while their co‐twin had none of those. Lung cancer was included in further analysis. We used Cox regression allowing for pair‐specific baseline functions to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). For tobacco‐related cancer sites, we recorded 7379 cases during median 27 years of follow‐up. The analyses based on individual twins showed that former (HR 1.31, 95% CI: 1.17‐1.48) and current (HR 2.14 [1.95‐2.34]) smokers are at increased risk to develop one of cancers listed above, compared to never smokers. Among 109 monozygotic twin pairs discordant for cancer and smoking, the HR was 1.85 (95% CI: 1.15‐2.98) among current smokers and 1.69 (1.00‐2.87) among former smokers when compared to their never smoking co‐twin. Thus, associations of smoking with several cancers were replicated for discordant identical twin pairs. Analyses based on genetically informative data provide evidence consistent with smoking causing multiple cancers.

Genetics, shared environment, or individual experience? A cross-sectional study of the health status following SARS-CoV-2 infection in monozygotic and dizygotic twins

BACKGROUND

The clinical presentation of COVID-19 shows a remarkably broad spectrum of symptoms. Although studies with adult twins on SARS-CoV-2 infection are rare so far, the fact that there is a genetic component associated with the highly variable clinical outcomes of COVID-19 has already been highlighted in recent studies investigating potential candidate genes and polymorphisms. This is the first study of adult monozygotic (MZ) and dizygotic (DZ) twins concordantly affected by SARS-CoV-2 infection to estimate variances explained by genetic, shared, and individual environmental components of both somatic and psychological symptoms following SARS-CoV-2 infection.

MATERIALS AND METHODS

Data were collected from 10 adult twin pairs (5 MZ, 5 DZ) in which both twins already had a SARS-CoV-2 infection. A self-designed questionnaire, the Barthel Index, and the Multidimensional Fatigue Inventory (MFI) were used to assess various symptoms and health status following SARS-CoV-2 infection. Intra-class correlations were calculated, and the Falconer formula was used to quantify and differentiate the percentages of genetic influences as well as common environment and personal experiences on the examined traits. In addition, potential factors influencing symptom burden were examined and discussed.

RESULTS

We found high estimated heritability for mental impairment after SARS-CoV-2 infection (h ² = 1.158) and for general fatigue (h ² = 1.258). For symptom burden, reduced activity, and reduced motivation the individual environment appears to have the strongest influence. Other fatigue symptoms are influenced by genetic effects which range between 42.8 and 69.4%.

CONCLUSION

Both genetics and individual environment play a role in health status after SARS-CoV-2 infection-mental status could be influenced primarily by genetic make-up, whereas for symptom burden and certain fatigue dimensions, non-shared environment could play a more critical role. Possible individual factors influencing the course of the disease were identified. However, gene-environment interactions may still be a source of differences between twins, and the search for candidate genes remains crucial on the road to personalized medicine.

Frailty trajectories in three longitudinal studies of aging: Is the level or the rate of change more predictive of mortality?

BACKGROUND

frailty shows an upward trajectory with age, and higher levels increase the risk of mortality. However, it is less known whether the shape of frailty trajectories differs by age at death or whether the rate of change in frailty is associated with mortality.

OBJECTIVES

to assess population frailty trajectories by age at death and to analyse whether the current level of the frailty index (FI) i.e. the most recent measurement or the person-specific rate of change is more predictive of mortality.

METHODS

3,689 individuals from three population-based cohorts with up to 15 repeated measurements of the Rockwood frailty index were analysed. The FI trajectories were assessed by stratifying the sample into four age-at-death groups: <70, 70-80, 80-90 and >90 years. Generalised survival models were used in the survival analysis.

RESULTS

the FI trajectories by age at death showed that those who died at <70 years had a steadily increasing trajectory throughout the 40 years before death, whereas those who died at the oldest ages only accrued deficits from age ~75 onwards. Higher level of FI was independently associated with increased risk of mortality (hazard ratio 1.68, 95% confidence interval 1.47-1.91), whereas the rate of change was no longer significant after accounting for the current FI level. The effect of the FI level did not weaken with time elapsed since the last measurement.

CONCLUSIONS

Frailty trajectories differ as a function of age-at-death category. The current level of FI is a stronger marker for risk stratification than the rate of change.

Systemic Inflammation in Preclinical Ulcerative Colitis

BACKGROUND & AIMS

Preclinical ulcerative colitis is poorly defined. We aimed to characterize the preclinical systemic inflammation in ulcerative colitis, using a comprehensive set of proteins.

METHODS

We obtained plasma samples biobanked from individuals who developed ulcerative colitis later in life (n = 72) and matched healthy controls (n = 140) within a population-based screening cohort. We measured 92 proteins related to inflammation using a proximity extension assay. The biologic relevance of these findings was validated in an inception cohort of patients with ulcerative colitis (n = 101) and healthy controls (n = 50). To examine the influence of genetic and environmental factors on these markers, a cohort of healthy twin siblings of patients with ulcerative colitis (n = 41) and matched healthy controls (n = 37) were explored.

RESULTS

Six proteins (MMP10, CXCL9, CCL11, SLAMF1, CXCL11 and MCP-1) were up-regulated (P < .05) in preclinical ulcerative colitis compared with controls based on both univariate and multivariable models. Ingenuity Pathway Analyses identified several potential key regulators, including interleukin-1β, tumor necrosis factor, interferon-gamma, oncostatin M, nuclear factor-κB, interleukin-6, and interleukin-4. For validation, we built a multivariable model to predict disease in the inception cohort. The model discriminated treatment-naïve patients with ulcerative colitis from controls with leave-one-out cross-validation (area under the curve = 0.92). Consistently, MMP10, CXCL9, CXCL11, and MCP-1, but not CCL11 and SLAMF1, were significantly up-regulated among the healthy twin siblings, even though their relative abundances seemed higher in incident ulcerative colitis.

CONCLUSIONS

A set of inflammatory proteins are up-regulated several years before a diagnosis of ulcerative colitis. These proteins were highly predictive of an ulcerative colitis diagnosis, and some seemed to be up-regulated already at exposure to genetic and environmental risk factors.

Toward more rigorous and informative nutritional epidemiology: The rational space between dismissal and defense of the status quo

To date, nutritional epidemiology has relied heavily on relatively weak methods including simple observational designs and substandard measurements. Despite low internal validity and other sources of bias, claims of causality are made commonly in this literature. Nutritional epidemiology investigations can be improved through greater scientific rigor and adherence to scientific reporting commensurate with research methods used. Some commentators advocate jettisoning nutritional epidemiology entirely, perhaps believing improvements are impossible. Still others support only normative refinements. But neither abolition nor minor tweaks are appropriate. Nutritional epidemiology, in its present state, offers utility, yet also needs marked, reformational renovation. Changing the status quo will require ongoing, unflinching scrutiny of research questions, practices, and reporting-and a willingness to admit that "good enough" is no longer good enough. As such, a workshop entitled "Toward more rigorous and informative nutritional epidemiology: the rational space between dismissal and defense of the status quo" was held from July 15 to August 14, 2020. This virtual symposium focused on: (1) Stronger Designs, (2) Stronger Measurement, (3) Stronger Analyses, and (4) Stronger Execution and Reporting. Participants from several leading academic institutions explored existing, evolving, and new better practices, tools, and techniques to collaboratively advance specific recommendations for strengthening nutritional epidemiology.

Association of body mass index and its long-term changes with cardiometabolic diseases: A nationwide twin study

BACKGROUND & AIMS

The association between higher body mass index (BMI) and cardiometabolic diseases (CMDs, including type 2 diabetes and cardiovascular diseases) is not well understood. We aimed to examine the association of BMI and its long-term changes with cardiometabolic diseases (CMDs) and explore the role of familial background and healthy lifestyle in this association.

METHODS

Within the Swedish Twin Registry, 36 622 CMD-free individuals aged ≥40 were followed for up to 16 years. BMI data was collected at baseline and 25-35 years prior to baseline. Healthy lifestyle (non-smoking, no/mild alcohol consumption, and regular physical activity) was assessed as unfavourable (none or only one of these factors) vs. favourable (two or three). Incident CMDs were identified by linkage with the Swedish National Patient Registry. Two strategies were followed: 1) Cox models in all twin individuals; 2) stratified Cox models in CMD-discordant twin pairs.

RESULTS

At baseline, 16 195 (44.2%) study participants had overweight/obesity (BMI ≥ 25 kg/m²) and 11 202 (30.6%) developed CMDs over follow-up. Among all participants, the hazard ratio (HR) and 95% confidence interval (CI) of developing any CMD was 1.52 (1.45-1.58) for people with overweight/obesity compared to normal BMI (20-25 kg/m²). Compared to stable normal BMI, HRs (95% CIs) of CMDs were 1.28 (1.02-1.59) and 1.33 (1.24-1.43) for only earlier life or only later life overweight/obesity, respectively, and 1.69 (1.55-1.85) for overweight/obesity both in earlier and later life. In stratified Cox analyses conducted among all CMD-discordant twin pairs, overweight/obesity was associated with greater risk of CMDs (1.37, 95% CI 1.18-1.61). In joint effect analysis, the risk of CMDs related to overweight/obesity was diminished 32% among people with a favourable lifestyle (1.51, 95% CI 1.44-1.58) compared to those with overweight/obesity and an unfavourable lifestyle (2.20, 95% CI 2.03-2.38).

CONCLUSIONS

Overweight/obesity is associated with an increased risk of CMDs, and shared genetic and early-life environmental factors might not account for this association. However, a favourable lifestyle could attenuate the risk of high BMI-related CMDs.