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Some preliminary research suggests higher rates of gastrointestinal disease in individuals with eating disorders (EDs). However, research is limited, and it remains unknown what etiologic factors account for observed associations. This was the first study to examine how EDs and dimensional ED symptoms (e.g. body dissatisfaction, binge eating) are phenotypically and etiologically associated with gastrointestinal disease in a large, population-based twin sample.
Adult female (N = 2980) and male (N = 2903) twins from the Michigan State University Twin Registry reported whether they had a lifetime ED (anorexia nervosa, bulimia nervosa, or binge-eating disorder) and completed a measure of dimensional ED symptoms. We coded the presence/absence of lifetime gastrointestinal disease (e.g. inflammatory bowel disease) based on responses to questions regarding chronic illnesses and medications. We first examined whether twins with gastrointestinal disease had higher rates of EDs and ED symptoms, then used correlated factors twin models to investigate genetic and environmental contributions to the overlap between disorders.
Twins with gastrointestinal disease had significantly greater dimensional ED symptoms (β = 0.21, p < 0.001) and odds of a lifetime ED (OR 2.90, p = 0.001), regardless of sex. Shared genetic factors fully accounted for the overlap between disorders, with no significant sex differences in etiologic associations.
Comorbidity between EDs and gastrointestinal disease may be explained by overlap in genetic influences, potentially including inflammatory genes implicated in both types of disorders. Screening for gastrointestinal disease in people with EDs, and EDs in those with gastrointestinal disease, is warranted.
Youth experiencing socioeconomic deprivation may be exposed to disadvantage in multiple contexts (e.g., neighborhood, family, and school). To date, however, we know little about the underlying structure of socioeconomic disadvantage, including whether the 'active ingredients' driving its robust effects are specific to one context (e.g., neighborhood) or whether the various contexts increment one another as predictors of youth outcomes.
The present study addressed this gap by examining the underlying structure of socioeconomic disadvantage across neighborhoods, families, and schools, as well as whether the various forms of disadvantage jointly predicted youth psychopathology and cognitive performance. Participants were 1,030 school-aged twin pairs from a subsample of the Michigan State University Twin Registry enriched for neighborhood disadvantage.
Two correlated factors underlay the indicators of disadvantage. Proximal disadvantage comprised familial indicators, whereas contextual disadvantage represented deprivation in the broader school and neighborhood contexts. Results from exhaustive modeling analyses indicated that proximal and contextual disadvantage incremented one another as predictors of childhood externalizing problems, disordered eating, and reading difficulties, but not internalizing symptoms.
Disadvantage within the family and disadvantage in the broader context, respectively, appear to represent distinct constructs with additive influence, carrying unique implications for multiple behavioral outcomes during middle childhood.
Twin studies demonstrate significant environmental influences and a lack of genetic effects on disordered eating before puberty in girls. However, genetic factors could act indirectly through passive gene–environment correlations (rGE; correlations between parents’ genes and an environment shaped by those genes) that inflate environmental (but not genetic) estimates. The only study to explore passive rGE did not find significant effects, but the full range of parental phenotypes (e.g., internalizing symptoms) that could impact daughters’ disordered eating was not examined. We addressed this gap by exploring whether parents’ internalizing symptoms (e.g., anxiety, depressive symptoms) contribute to daughters’ eating pathology through passive rGE. Participants were female twin pairs (aged 8–14 years; M = 10.44) in pre-early puberty and their biological parents (n = 279 families) from the Michigan State University Twin Registry. Nuclear twin family models explored passive rGE for parents’ internalizing traits/symptoms and twins’ overall eating disorder symptoms. No evidence for passive rGE was found. Instead, environmental factors that create similarities between co-twins (but not with their parents) and unique environmental factors were important. In pre-early puberty, genetic factors do not influence daughters’ disordered eating, even indirectly through passive rGE. Future research should explore sibling-specific and unique environmental factors during this critical developmental period.
Deficits in executive functioning both run in families and serve as a transdiagnostic risk factor for psychopathology. The present study employed twin modeling to examine parenting as an environmental pathway underlying the intergenerational transmission of executive functioning in an at-risk community sample of children and adolescents (N = 354 pairs, 167 monozygotic). Using structural equation modeling of multi-informant reports of parenting and a multi-method measure of child executive functioning, we found that better parent executive functioning related to less harsh, warmer parenting, which in turn related to better child executive functioning. Second, we assessed the etiology of executive functioning via the nuclear twin family model, finding large non-shared environmental effects (E = .69) and low-to-moderate heritability (A = .22). We did not find evidence of shared environmental effects or passive genotype–environment correlation. Third, a bivariate twin model revealed significant shared environmental overlap between both warm and harsh parenting and child executive functioning (which may indicate either passive genotype–environment correlation or environmental mediation), and non-shared environmental overlap between only harsh parenting and child executive functioning (indicating an effect of harsh parenting separable from genetic confounds). In summary, genetics contribute to the intergenerational transmission of executive functioning, with environmental mechanisms, including harsh parenting, also making unique contributions.
Stress is associated with binge eating and emotional eating (EE) cross-sectionally. However, few studies have examined stress longitudinally, limiting understanding of how within-person fluctuations in stress influence EE over time and whether stress is a risk factor or consequence of EE. Additionally, little is known regarding how the biological stress response relates to EE.
We used an intensive, longitudinal design to examine between-person and within-person effects of major life stress, daily stress, and cortisol on EE in a population-based sample of women (N = 477; ages 15–30; M = 21.8; s.d. = 3.0) from the Michigan State University Twin Registry. Participants reported past year major life stress, then provided daily ratings of EE and stress for 49 consecutive days. Hair cortisol concentration (HCC) was collected as a longitudinal biological stress measure.
Women reported greater EE when they experienced greater mean stress across days (between-person effects) or greater stress relative to their own average on a given day (within-person effects). Daily stress was more strongly associated with EE than major life stress. However, the impact of daily stress on EE was amplified in women with greater past year major life stress. Finally, participants with lower HCC had increased EE.
Findings confirm longitudinal associations between stress and EE in women, and highlight the importance of within-person shifts in stress in EE risk. Results also highlight HCC as a novel biological stress measure that is significantly associated with EE and may overcome limitations of prior physiological stress response indicators.
Women show a heightened risk for psychosis in midlife that is not observed in men. The menopausal transition (i.e. perimenopause) and accompanying changes in ovarian hormones are theorized to account for this midlife increase in risk. This narrative review aims to empirically examine these theories by reviewing studies of midlife and perimenopausal psychosis risk in women and potential ovarian hormone mechanisms of effects. Clinical and pre-clinical studies examining the effects of midlife age, menopausal stage, and ovarian hormones across adulthood on psychosis risk were identified. Synthesis of this body of work revealed that the peak ages of midlife psychosis risk in women overlap with the age range of key menopausal stages (especially the perimenopausal transition), although studies directly assessing menopausal stage are lacking. Studies examining ovarian hormone effects have almost exclusively focused on earlier developmental stages and events (e.g. pregnancy, the menstrual cycle) and show increases in psychotic symptoms in women and female rats during periods of lower estradiol levels. Estrogen treatment also tends to enhance the effects of neuroleptics in females across species at various reproductive phases. Initial data are promising in suggesting a role for menopausal stage and ovarian hormones in psychosis risk. However, critical gaps in our knowledge base remain, as there is a tendency to rely on indirect and proxy measures of menopausal status and hormones. Opportunities for future research are discussed with the goal of increasing research in this critical area of women's health.
In 1942, Shaw and McKay reported that disadvantaged neighborhoods predict youth psychopathology (Shaw & McKay, 1942). In the decades since, dozens of papers have confirmed and extended these early results, convincingly demonstrating that disadvantaged neighborhood contexts predict elevated rates of both internalizing and externalizing disorders across childhood and adolescence. It is unclear, however, how neighborhood disadvantage increases psychopathology.
Our study sought to fill this gap in the literature by examining the Area Deprivation Index (ADI), a composite measure of Census tract disadvantage, as an etiologic moderator of several common forms of psychopathology in two samples of school-aged twins from the Michigan State University Twin Registry (N = 4815 and 1030 twin pairs, respectively), the latter of which was enriched for neighborhood disadvantage.
Across both samples, genetic influences on attention-deficit hyperactivity problems were accentuated in the presence of marked disadvantage, while nonshared environmental contributions to callous-unemotional traits increased with increasing disadvantage. However, neighborhood disadvantage had little moderating effect on the etiology of depression, anxiety, or somatic symptoms.
Such findings suggest that, although neighborhood disadvantage does appear to serve as a general etiologic moderator of many (but not all) forms of psychopathology, this etiologic moderation is phenotype-specific.
Conventional longitudinal behavioral genetic models estimate the relative contribution of genetic and environmental factors to stability and change of traits and behaviors. Longitudinal models rarely explain the processes that generate observed differences between genetically and socially related individuals. We propose that exchanges between individuals and their environments (i.e., phenotype–environment effects) can explain the emergence of observed differences over time. Phenotype–environment models, however, would require violation of the independence assumption of standard behavioral genetic models; that is, uncorrelated genetic and environmental factors. We review how specification of phenotype–environment effects contributes to understanding observed changes in genetic variability over time and longitudinal correlations among nonshared environmental factors. We then provide an example using 30 days of positive and negative affect scores from an all-female sample of twins. Results demonstrate that the phenotype–environment effects explain how heritability estimates fluctuate as well as how nonshared environmental factors persist over time. We discuss possible mechanisms underlying change in gene–environment correlation over time, the advantages and challenges of including gene–environment correlation in longitudinal twin models, and recommendations for future research.
The primary aim of the Michigan State University Twin Registry (MSUTR) is to examine developmental differences in genetic, environmental, neural, epigenetic, and neurobiological influences on psychopathology and resilience, particularly during childhood and adolescence. The MSUTR has two broad components: a large-scale, population-based registry of child, adolescent, and adult twins and their families (current N ~30,000) and a series of more focused and in-depth studies drawn from the registry (projected N ~7200). Participants in the population-based registry complete a family health and demographic questionnaire via mail. Families can then be recruited for one or more of the intensive, in-person studies from the population-based registry, using any one of several recruitment strategies (e.g., population-based, based on their answers to the registry questionnaire). These latter studies target a variety of biological, genetic, and environmental phenotypes, including multi-informant measures of psychiatric and behavioral phenotypes, functional and structural neuroimaging, comprehensive measures of the twin family environment (e.g., census and neighborhood informant reports of twin neighborhood characteristics, videotaped interactions of child twin families), buccal swab and salivary DNA samples, and/or assays of adolescent and adult steroid hormone levels. This article provides an overview of the MSUTR and describes current and future research directions.
Prior work has robustly suggested that social processes in the neighborhood (i.e. informal social control, social cohesion, norms) influence child conduct problems (CP) and related outcomes, but has yet to consider how these community-level influences interact with individual-level genetic risk for CP. The current study sought to do just this, evaluating neighborhood-level social processes as etiologic moderators of child CP for the first time.
We made use of two nested samples of child and adolescent twins within the Michigan State University Twin Registry (MSUTR): 5649 families who participated in in the Michigan Twins Project (MTP) and 1013 families who participated in the Twin Study of Behavioral and Emotional Development (TBED-C). The neighborhood social processes of informal social control, social cohesion, and norms were assessed using neighborhood sampling techniques, in which residents of each twin family's neighborhood reported on the social processes in their neighborhood. Standard biometric GxE analyses evaluated the extent to which they moderated the etiology of CP.
The ‘no moderation’ model provided the best fit to the data in nearly all cases, arguing against neighborhood social processes as etiologic moderators of youth CP.
The neighborhood social processes evaluated here do not appear to exert their effects on child CP via etiologic moderation. The documented links between neighborhood social processes and child CP are thus likely to reflect a different etiologic process. Possibilities include environmental main effects of neighborhood social processes on child CP, or genotype-environment correlations.
Available twin-family data on sex differences in antisocial behavior (ASB) simultaneously suggest that ASB is far more prevalent in males than in females, and that its etiology (i.e. the effects of genes, environments, hormones, culture) does not differ across sex. This duality presents a conundrum: How do we make sense of mean sex differences in ASB if not via differences in genes, environments, hormones, and/or cultures? The current selective review and critique explores possible contributions to these seemingly incompatible sets of findings. We asked whether the presence of sex differences in behavior could be smaller than is typically assumed, or confined to a specific set of behaviors. We also asked whether there might be undetected differences in etiology across sex in twin-family studies. We found little evidence that bias or measurement invariance across sex account for phenotypic sex differences in ASB, but we did identify some key limitations to current twin-family approaches. These included the questionable ability of qualitative sex difference analyses to detect gender norms and prenatal exposure to testosterone, and concerns regarding specific analytic components of quantitative sex difference analyses. We conclude that the male preponderance in ASB is likely to reflect a true sex difference in observed behavior. It was less clear, however, that the genetic and environmental contributions to ASB are indeed identical across sex, as argued by prior twin-family studies. It is our hope that this review will inspire the development of new, genetically-informed methods for studying sex differences in etiology.
Callous-unemotional (CU) traits are critical to developmental, diagnostic, and clinical models of antisocial behaviors (AB). However, assessments of CU traits within large-scale longitudinal and neurobiologically focused investigations remain remarkably sparse. We sought to develop a brief measure of CU traits using items from widely administered instruments that could be linked to neuroimaging, genetic, and environmental data within already existing datasets and future studies.
Data came from a large and diverse sample (n = 4525) of youth (ages~9–11) taking part in the Adolescent Brain and Cognitive Development (ABCD) Study. Moderated nonlinear factor analysis was used to assess measurement invariance across sex, race, and age. We explored whether CU traits were distinct from other indicators of AB, investigated unique links with theoretically-relevant outcomes, and replicated findings in an independent sample.
The brief CU traits measure demonstrated strong psychometric properties and evidence of measurement invariance across sex, race, and age. On average, boys endorsed higher levels of CU traits than girls and CU traits were related to, yet distinguishable from other indicators of AB. The CU traits construct also exhibited expected associations with theoretically important outcomes. Study findings were also replicated across an independent sample of youth.
In a large, multi-site study, a brief measure of CU traits can be measured distinctly from other dimensions of AB. This measure provides the scientific community with a method to assess CU traits in the ABCD sample, as well as in other studies that may benefit from a brief assessment of CU.
Prior work has indicated both theoretical and empirical overlap between social and physical aggression. The extent to which their covariance can be explained by the same underlying genetic or environmental factors, however, remains unclear. It is also uncertain whether or how the origins of their covariance might vary across sex. The current study sought to fill these gaps in the literature.
We examined maternal and teacher reports of youth physical and social aggression in over 1000 6–10 years old (mean age = 8.02 years) twin pairs from the Michigan State University Twin Registry. We made use of the bivariate correlated factors model to clarify the origins of their association. We further tested both sex difference and no-sex difference versions of that model to determine whether there are sex differences in the association between social and physical aggression, as often assumed.
The covariation between social and physical aggression was due to overlapping genetic factors and common environmental conditions. Specifically, 50–57% of the genetic factors, 74–100% of the shared environmental factors, and 28–40% of the unique environmental factors influencing physical aggression also influenced social aggression according to both mother and teacher reports. These shared etiological factors did not differ across sex.
These findings argue against the common assumption that social aggression is the ‘female version’ of male physical aggression, and instead suggest that social aggression may be best conceptualized as a form of antisocial behavior that shares developmental pathways with other manifestations of externalizing pathology.
Although there is growing recognition that disadvantaged contexts attenuate genetic influences on youth misbehavior, it is not yet clear how this dampening occurs. The current study made use of a “geographic contagion” model to isolate specific contexts contributing to this effect, with a focus on nonaggressive rule-breaking behaviors (RB) in the families’ neighbors. Our sample included 847 families residing in or near modestly-to-severely disadvantaged neighborhoods who participated in the Michigan State University Twin Registry. Neighborhood sampling techniques were used to recruit neighbors residing within 5km of a given family (the mean number of neighbors assessed per family was 13.09; range, 1–47). Analyses revealed clear evidence of genotype–environment interactions by neighbor RB, such that sibling-level shared environmental influences on child RB increased with increasing neighbor self-reports of their own RB, whereas genetic influences decreased. Moreover, this moderation appeared to be driven by geographic proximity to neighbors. Sensitivity analyses further indicated that this effect was specifically accounted for by higher levels of neighbor joblessness, rather than elements of neighbor RB that would contribute to neighborhood blight or crime. Such findings provocatively suggest that future genotype–environment interactions studies should integrate the dynamic networks of social contagion theory.
Social aggression is a form of antisocial behavior in which social relationships and social status are used to damage reputations and inflict emotional harm on others. Despite extensive research examining the prevalence and consequences of social aggression, only a few studies have examined its genetic–environmental etiology, with markedly inconsistent results.
We estimated the etiology of social aggression using the nuclear twin family (NTF) model. Maternal-report, paternal-report, and teacher-report data were collected for twin social aggression (N = 1030 pairs). We also examined the data using the classical twin (CT) model to evaluate whether its strict assumptions may have biased previous heritability estimates.
The best-fitting NTF model for all informants was the ASFE model, indicating that additive genetic, sibling environmental, familial environmental, and non-shared environmental influences significantly contribute to the etiology of social aggression in middle childhood. However, the best-fitting CT model varied across informants, ranging from AE and ACE to CE. Specific heritability estimates for both NTF and CT models also varied across informants such that teacher reports indicated greater genetic influences and father reports indicated greater shared environmental influences.
Although the specific NTF parameter estimates varied across informants, social aggression generally emerged as largely additive genetic (A = 0.15–0.77) and sibling environmental (S = 0.42–0.72) in origin. Such findings not only highlight an important role for individual genetic risk in the etiology of social aggression, but also raise important questions regarding the role of the environment.
Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990–1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.
We analyzed birth order differences in means and variances of height and body mass index (BMI) in monozygotic (MZ) and dizygotic (DZ) twins from infancy to old age. The data were derived from the international CODATwins database. The total number of height and BMI measures from 0.5 to 79.5 years of age was 397,466. As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood. After adjusting the results for birth weight, the birth order differences decreased and were no longer statistically significant. First-born twins had greater BMI than the second-born twins over childhood and adolescence. After adjusting the results for birth weight, birth order was still associated with BMI until 12 years of age. No interaction effect between birth order and zygosity was found. Only limited evidence was found that birth order influenced variances of height or BMI. The results were similar among boys and girls and also in MZ and DZ twins. Overall, the differences in height and BMI between first- and second-born twins were modest even in early childhood, while adjustment for birth weight reduced the birth order differences but did not remove them for BMI.
A trend toward greater body size in dizygotic (DZ) than in monozygotic (MZ) twins has been suggested by some but not all studies, and this difference may also vary by age. We analyzed zygosity differences in mean values and variances of height and body mass index (BMI) among male and female twins from infancy to old age. Data were derived from an international database of 54 twin cohorts participating in the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), and included 842,951 height and BMI measurements from twins aged 1 to 102 years. The results showed that DZ twins were consistently taller than MZ twins, with differences of up to 2.0 cm in childhood and adolescence and up to 0.9 cm in adulthood. Similarly, a greater mean BMI of up to 0.3 kg/m2 in childhood and adolescence and up to 0.2 kg/m2 in adulthood was observed in DZ twins, although the pattern was less consistent. DZ twins presented up to 1.7% greater height and 1.9% greater BMI than MZ twins; these percentage differences were largest in middle and late childhood and decreased with age in both sexes. The variance of height was similar in MZ and DZ twins at most ages. In contrast, the variance of BMI was significantly higher in DZ than in MZ twins, particularly in childhood. In conclusion, DZ twins were generally taller and had greater BMI than MZ twins, but the differences decreased with age in both sexes.
For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.
The behavior genetic literature suggests that genetically influenced characteristics of the child elicit specific behaviors from the parent. However, little is known about the processes by which genetically influenced child characteristics evoke parental responses. Interpersonal theory provides a useful framework for identifying reciprocal behavioral processes between children and mothers. The theory posits that, at any given moment, interpersonal behavior varies along the orthogonal dimensions of warmth and control and that the interpersonal behavior of one individual tends to elicit corresponding or contrasting behavior from the other (i.e., warmth elicits warmth, whereas control elicits submission). The current study thus examined these dimensions of interpersonal behavior as they relate to the parent–child relationship in 546 twin families. A computer joystick was used to rate videos of mother–child interactions in real time, yielding information on mother and child levels of warmth and control throughout the interaction. Analyses indicated that maternal control, but not maternal warmth, was influenced by evocative gene–environment correlational processes, such that genetic influences on maternal control and child control were largely overlapping. Moreover, these common genetic influences were present both cross-sectionally and over the course of the interaction. Such findings not only confirm the presence of evocative gene–environment correlational processes in the mother–child relationship but also illuminate at least one of the specific interpersonal behaviors that underlie this evocative process.