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AbstractThe 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.

The primary aim of the Michigan State University Twin Registry (MSUTR) is on understanding developmental changes in genetic, environmental, and neurobiological influences on internalizing and externalizing disorders, with antisocial behavior and disordered eating representing our particular areas of interest. The MSUTR has two broad components: a large-scale, population-based registry of child, adolescent, and adult twins and their families (currentN~20,000) and a series of more focused and in-depth studies drawn from the registry (currentN~4,000). Participants in the population-based registry complete a family health and demographic questionnaire via mail. Families are then recruited for one or more of the intensive, in-person studies from the population-based registry based on their answers to relevant items in the registry questionnaire. These in-person assessments target a variety of biological, genetic, and environmental phenotypes, including multi-informant measures of psychiatric and behavioral phenotypes, census and neighborhood informant reports of twin neighborhood characteristics, buccal swab and salivary DNA samples, assays of adolescent and adult steroid hormone levels, and/or videotaped interactions of child twin families. This article provides an overview of the MSUTR and describes current and future research directions.

Rates of twinning have risen dramatically over the last 30 years, from 1 in 53 births in 1980 to 1 in 30 births in 2009 (Martin et al. (January 2012). Three decades of twin births in the United States, 1980–2009. Atlanta, GA: Centers for Disease Control and Prevention, National Center for Health Statistics). This increase is largely attributable to increases in the use of fertility treatments (i.e., ovulation induction and in vitro fertilization) combined with delays in parenthood. Although this increase means that more twins are available for recruitment into twin studies, it also has potential consequences for the heritability estimates obtained in these studies. This study sought to evaluate this possibility, making use of the ongoing Michigan Twins Project (N = 7,261 families with twins aged 3–17 years), an arm of the Michigan State University Twin Registry. Results revealed that, on average, twins conceived via fertility treatments had lower rates of behavior problems than those conceived naturally, although these behavioral differences could be explained largely by demographic and socio-economic differences across the two types of twin families. Twin similarity did not meaningfully differ across fertility treatment status. We thus conclude that estimates of genetic and environmental influences obtained from twin studies over the last 10–15 years are more or less unaffected by the inclusion of twins conceived via fertility treatments in their samples.

AbstractA recent study has suggested that aggressive (AGG) and non-aggressive, rule-breaking (RB) antisocial behavior evidence differential and subtype-specific patterns of genetic expression during development. Namely, although genetic influences on RB increase dramatically during early- to mid-adolescence, genetic influences on AGG appear to remain stable. As no other study has examined age-related change in AGG versus RB, more research is clearly needed before any firm conclusions can be drawn. The current study thus examined whether and how age impacted genetic and environmental influences on AGG and RB in a sample of 252 10- to 15-year-old twin pairs assessed as part of the Michigan State University Twin Registry (MSUTR). Results constructively replicated and extended prior findings, indicating that while the magnitude of genetic and environmental influences on AGG remained stable across adolescence, genetic influences on RB increased dramatically with age. Such findings provide additional support for etiological distinctions within the broader construct of antisocial behavior based on the presence or absence of aggression, and offer insights into the expression of genetic influences during development.

AbstractThe primary aim of the Michigan State University Twin Registry (MSUTR) is to examine developmental differences in genetic, environmental, and neurobiological influences on internalizing and externalizing symptoms, with disordered eating and antisocial behavior representing particular areas of interest. Twin participants span several developmental stages (i.e., childhood, adolescence, and young adulthood). Assessments include comprehensive, multiinformant measures of psychiatric and behavioral phenotypes, buccal swab and salivary DNA samples, assays of adolescent and adult steroid hormone levels (e.g., estradiol, progesterone, testosterone, cortisol), and videotaped parent–child interactions of child and adolescent twin families. To date, we have collected data on over 1000 twins, with additional data collections underway. This article provides an overview of the newly developed MSUTR and describes current and future research directions.

Prior research has suggested that disadvantaged neighborhood contexts alter the etiology of youth antisocial behavior (ASB). Unfortunately, these studies have relied exclusively on governmental data collected in administratively-defined neighborhoods (e.g., Census tracts or block groups, zip codes), a less than optimal approach for studying neighborhood effects. It would thus be important to extend prior findings of GxE using neighborhood sampling techniques, in which disadvantage is assessed via resident informant-reports of the neighborhood. The current study sought to do just this, examining two independent twin samples from the Michigan State University Twin Registry. Neighborhood disadvantage was assessed via maternal and neighbor informant-reports, the latter of which were analyzed multiple ways (i.e., all neighbors within 1km, nearest neighbor, and all neighbors within the County). Analyses revealed clear and consistent evidence of moderation by neighborhood disadvantage, regardless of informant or the specific operationalization of neighborhood. Shared environmental influences on ASB were observed to be several-fold larger in disadvantaged contexts, while genetic influences were proportionally more influential in advantaged neighborhoods. Such findings indicate that neighborhood disadvantage exerts rather profound effects on the origins of youth ASB. Efforts should now be made to identify the active ingredients of neighborhood disadvantage.

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.

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.