The aim of the Avera Twin Register (ATR) is to establish a prospective longitudinal repository of twins, multiples, siblings and family members’ biological samples to study environmental and genetic influences on health and disease. Also, it is our intention to contribute to international genome-wide association study (GWAS) twin consortia when appropriate sample size is achieved within the ATR. The ATR is young compared with existing registers and continues to collect a longitudinal repository of biological specimens, survey data and health information. Data and biological specimens were originally collected via face-to-face appointments or the postal department and consisted of paper-informed consents and questionnaires. Enrollment of the ATR began on May 18, 2016 and is located in Sioux Falls, South Dakota, a rural and frontier area in the Central United States with a regional population of approximately 880,000. The original target area for the ATR was South Dakota and the four surrounding states: Minnesota, Iowa, North Dakota and Nebraska. The ATR has found a need to expand that area based on twin and multiple siblings who live in various areas surrounding these states. A description of the state of the ATR today and its transition to online data collection and informed consent will be presented. The ATR collects longitudinal data on lifestyle, including diet and activity levels, aging, plus complex traits and diseases. All twins and multiples participating in the ATR are genotyped on the Illumina Global Screening Array and receive zygosity results.

The Boston University Twin Project (BUTP) uses a multimethod, longitudinal approach to study the role of genetic and environmental factors on the development of child temperament and related behaviors in early childhood. There are two phases in this project. The first, described in the previous Twin Research and Human Genetics special issue on twin registries, focused on activity level and comprised over 300 twin pairs assessed in the home and laboratory at ages 2 and 3. In this article, we describe subject recruitment, sample characteristics, and study procedures and measures of the second phase of the BUTP. This recent study focuses more broadly on the development of multiple temperament dimensions and explores associations between temperament trajectories, parenting and child adjustment in a new cohort of approximately 300 twin pairs assessed at 3, 4 and 5 years of age.

The purpose of this update is to provide the most current information about both the Colorado Adoption Project (CAP) and the Longitudinal Twin Study (LTS) and to introduce the Colorado Adoption/Twin Study of Lifespan behavioral development and cognitive aging (CATSLife), a product of their merger and a unique study of lifespan behavioral development and cognitive aging. The primary objective of CATSLife is to assess the unique saliency of early childhood genetic and environmental factors to adult cognitive maintenance and change, as well as proximal influences and innovations that emerge across development. CATSLife is currently assessing up to 1600 individuals on the cusp of middle age, targeting those between 30 and 40 years of age. The ongoing CATSLife data collection is described as well as the longitudinal data available from the earlier CAP and LTS assessments. We illustrate CATSLife via current projects and publications, highlighting the measurement of genetic, biochemical, social, sociodemographic and environmental indices, including geospatial features, and their impact on cognitive maintenance in middle adulthood. CATSLife provides an unparalleled opportunity to assess prospectively the etiologies of cognitive change and test the saliency of early childhood versus proximal influences on the genesis of cognitive decline.

The Colorado Twin Registry (CTR) is a population-based registry formed from birth and school records including twins born between 1968 and the present. Two previous reports on the CTR [Rhea et al., (2006). Twin Research and Human Genetics, 9, 941–949; Rhea et al., (2013).Twin Research and Human Genetics, 16, 351–357] covered developments in the CTR through 2012. This report briefly summarizes previously presented material on ascertainment and recruitment and the relationships between samples and studies, discusses developments since 2012 for four previously described twin samples, describes two new samples and their complementary studies and expands on two subjects briefly mentioned in the last report: a history of genotyping efforts involving CTR samples, and a survey of collaborations and consortia in which CTR twins have been included. The CTR remains an active resource for both ongoing, longitudinal research and the recruitment of new twin samples for newly identified research opportunities.

The Early Growth and Development Study (EGDS) is a prospective adoption study of birth parents, adoptive parents and adopted children (n = 561 adoptees). The original sample has been expanded to include siblings of the EGDS adoptees who were reared by the birth mother and assessed beginning at age 7 years (n = 217 biological children), and additional siblings in both the birth and adoptive family homes, recruited when the adoptees were 8–15 years old (n = 823). The overall study aims are to examine how family, peer and contextual processes affect child and adolescent adjustment, and to examine their interplay (mediation, moderation) with genetic influences. Adoptive and birth parents were originally recruited through adoption agencies located throughout the USA following the birth of a child. Assessments are ongoing and occurred in 9 month’s intervals until the adoptees turned 3 years of age, and in 1 to 2 year intervals thereafter through age 15. Data collection includes the following primary constructs: child temperament, behavior problems, mental health, peer relations, executive functioning, school performance and health; birth and adoptive parent personality characteristics, mental health, health, context, substance use, parenting and marital relations; and the prenatal environment. Findings highlight the power of the adoption design to detect environmental influences on child development and provide evidence of complex interactions and correlations between genetic, prenatal environmental and postnatal environmental influences on a range of child outcomes. The study sample, procedures and an overview of findings are summarized and ongoing assessment activities are described.

The Florida State Twin Registry has existed for nearly two decades, and it grew primarily over 10 years as part of the Florida Learning Disability Research Center at Florida State University. The registry contains 2753 sets of twins and other multiples in Florida. The mean age of the sample currently is 17.96 years (SD = 2.05). The registry is diverse in terms of race and ethnicity (49% White, 19% African American, 24% Hispanic and 8% mixed or other). The characteristics of the samples and measures in the studies that served to build the registry are outlined.

Virtual twins (VTs) are defined as same-age unrelated siblings raised together from early infancy. This special class of adoptive siblings replays the rearing situation of twins, absent genetic relatedness. The first such pair was identified and studied in 1990 at the University of Minnesota, leading to the creation of the Fullerton Virtual Twin Study (FVTS) at California State University, Fullerton (CSUF) the following year. The registry currently includes 169 VT pairs, mostly children, with new pairs identified on a regular basis. These sibling sets provide a direct estimate of environmental influences on developmental traits and, as such, offer informative comparisons with ordinary monozygotic and dizygotic twins, full siblings and adoptive brothers and sisters. The sample characteristics, assessment battery and findings to date are summarized in this 2019 update.

The Louisville Twin Study (LTS) is nationally recognized as one of the largest and most comprehensive studies of child development related to multiple birth status. The LTS is unique because of the extensive longitudinal face-to-face assessments, the frequency of data collection, the inclusion of data on additional family members (i.e., parents, siblings, grandparents; and later, twins’ own spouses and children), and the variety of data collection methods used. Data preservation efforts began in 2008 and are largely complete, although efforts are ongoing to obtain funding to convert the electronic data to a newer format. A pilot study was completed in the summer of 2018 to bring the twins, who are now middle-aged, back for testing. A grant is currently under review to extend the pilot study to include all former participants who are now ≥40 years of age. Opportunities for collaboration are welcome.

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.

The Minnesota Center for Twin and Family Research (MCTFR) comprises multiple longitudinal, community-representative investigations of twin and adoptive families that focus on psychological adjustment, personality, cognitive ability and brain function, with a special emphasis on substance use and related psychopathology. The MCTFR includes the Minnesota Twin Registry (MTR), a cohort of twins who have completed assessments in middle and older adulthood; the Minnesota Twin Family Study (MTFS) of twins assessed from childhood and adolescence into middle adulthood; the Enrichment Study (ES) of twins oversampled for high risk for substance-use disorders assessed from childhood into young adulthood; the Adolescent Brain (AdBrain) study, a neuroimaging study of adolescent twins; and the Siblings Interaction and Behavior Study (SIBS), a study of adoptive and nonadoptive families assessed from adolescence into young adulthood. Here we provide a brief overview of key features of these established studies and describe new MCTFR investigations that follow up and expand upon existing studies or recruit and assess new samples, including the MTR Study of Relationships, Personality, and Health (MTR-RPH); the Colorado-Minnesota (COMN) Marijuana Study; the Adolescent Brain Cognitive Development (ABCD) study; the Colorado Online Twins (CoTwins) study and the Children of Twins (CoT) study.

The Mid-Atlantic Twin Registry (MATR) is a population-based registry of more than 60,000 twins primarily born or living in Virginia, North Carolina and South Carolina. Researchers may utilize the MATR for administration of research services, including study recruitment, data or sample (e.g., DNA) collection, archival dataset creation, as well as data collection through mailed, phone or online surveys. In addition, the MATR houses the MATR Repository, with over 1700 DNA samples primarily from whole blood available for researchers interested in DNA genotyping. For over 40 years MATR twins have participated in research studies with investigators from a range of scientific disciplines and institutions. These studies, which have resulted in numerous publications, explored diverse topics, including substance use, smoking behaviors, developmental psychopathology, bullying, children’s health, cardiovascular disease, cancer, the human microbiome, epigenetics of aging, children of twins and sleep homeostasis. Researchers interested in utilizing twins are encouraged to contact the MATR to discuss potential research opportunities.

The National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry is one of the oldest, national population-based twin registries in the USA. It comprises 15,924 White male twin pairs born in the years 1917–1927 (N = 31.848), both of whom served in the armed forces, chiefly during World War II. This article updates activities in this registry since the most recent report in Twin Research and Human Genetics (Page, 2006). Records-based data include information from enlistment charts and Veterans Administration data linkages. There have been three major epidemiologic questionnaires and an education and earnings survey. Separate data collection efforts with the NAS-NRC registry include the National Heart, Lung, and Blood Institute (NHLBI) subsample, the Duke Twins Study of Memory in Aging and a clinically based study of Parkinson’s disease. Progress has been made on consolidating the various data holdings of the NAS-NRC Twin Registry. Data that had been available through the National Academy of Sciences are now freely available through National Archive of Computerized Data on Aging (NACDA).

The National Project on Achievement in Twins (NatPAT) began in 2017 as part of the third funding cycle of the Florida Learning Disabilities Research Center, a program project grant funded by the Eunice Kennedy Shriver National Institute of Child Health and Development. NatPAT will have a nationally representative sample of elementary school-aged twins in the United States. The overall goal of the project is to uncover salient factors, including genetic and environmental influences, which contribute to the co-development of reading and math performance during the critical developmental period of elementary school. Here we present the specific aims, methods and materials, and future directions of the project.

The Pennsylvania Longitudinal Study of Parents and Children Twin Registry was developed to capture a representative sample of multiple births and their parents in the state of Pennsylvania. The registry has two main efforts. The first began in 2012 through recruitment of adolescents in Pennsylvania schools. The second effort began in January 2019 in partnership with the Pennsylvania Department of Health to capture the birth cohort of twins born from 2007 to 2017. Study recruitment, sample demographics, focus and measures are provided, as well as future directions.

The Project Talent Twin and Sibling (PTTS) study includes 4481 multiples and their 522 nontwin siblings from 2233 families. The sample was drawn from Project Talent, a U.S. national longitudinal study of 377,000 individuals born 1942–1946, first assessed in 1960 and representative of U.S. students in secondary school (Grades 9–12). In addition to the twins and triplets, the 1960 dataset includes 84,000 siblings from 40,000 other families. This design is both genetically informative and unique in facilitating separation of the ‘common’ environment into three sources of variation: shared by all siblings within a family, specific to twin-pairs, and associated with school/community-level factors. We term this the GIFTS model for genetics, individual, family, twin, and school sources of variance. In our article published in a previous Twin Research and Human Genetics special issue, we described data collections conducted with the full Project Talent sample during 1960–1974, methods for the recent linking of siblings within families, identification of twins, and the design of a 54-year follow-up of the PTTS sample, when participants were 68–72 years old. In the current article, we summarize participation and data available from this 2014 collection, describe our method for assigning zygosity using survey responses and yearbook photographs, illustrate the GIFTS model applied to 1960 vocabulary scores from more than 80,000 adolescent twins, siblings and schoolmates and summarize the next wave of PTTS data collection being conducted as part of the larger Project Talent Aging Study.

This article reviews the Southern Illinois Twins/Triplets and Siblings Study (SITSS) and describes some of the findings related to recent projects that were completed using this sample. At this time, the SITSS has enrolled 375 twin pairs, 12 triplet families, 1 family of quadruplets, 98 nontwin sibling pairs and 287 singletons. Testing begins for twins and triplets as young as age 1 and then occurs yearly on their birthdays until 5 years of age. Through age 20, various follow-up studies have been conducted on the SITSS sample to examine their social, emotional, and cognitive development across childhood and adolescence from a behavioral genetic perspective. A variety of methodologies have been used to investigate gene–environment correlations (rGE) and gene–environment interactions (GxE). Advanced statistical procedures (e.g., genetic likelihood indices and multilevel modeling) have been utilized to further investigate genetic underpinnings of behavior. Recent results have indicated genetic influences on the aggressiveness of preschoolers’ media preferences, increased problem behaviors related to young children’s overestimation of self-competence, and the influence of early life temperament and internalizing problems on adolescent health behaviors. Additionally, the SITSS has provided evidence for evocative rGE for various behaviors (aggression, prosocial and play), as well as findings supporting interactions between the dopamine receptor D4 gene (DRD4) and the environment (peer victimization, prenatal birth complications and parental sensitivity). Together, by use of multitrait and multimethodological investigations, this behavior genetic data set assists in furthering our understanding of biological and environmental influences on children’s development.

The Vietnam Era Twin Study of Aging (VETSA) is a longitudinal behavioral genetic study with a primary focus on cognitive and brain aging in men, particularly early identification of risk for mild cognitive impairment (MCI) and Alzheimer’s disease (AD). It comprises a subset of over 1600 twins from the Vietnam Era Twin Registry. Twins live all over the USA. Assessments began when participants were in their 50s. Follow-ups were conducted every 5–6 years, and wave 3 has been completed as of this writing. The age range of participants is narrow (about 10 years). An extensive neurocognitive test battery has added precision in assessing differences in middle-aged adults, and predicting progression to MCI. Young adult cognitive test data (at an average age of 20 years) provide a means of disentangling aging effects from longstanding differences. Genome wide genotyping and plasma assays of AD biomarkers from waves 1 and 3 were conducted in wave 3. These features make the VETSA ideal for studying the heterogeneity of within-individual trajectories from midlife to old age, and for early detection of risk factors for cognitive decline.

It has been over 5 years since the last special issue of Twin Research and Human Genetics on ‘Twin Registries Worldwide: An Important Resource for Scientific Research’ was published. Much progress has been made in the broad field of twin research since that time, and the current special issue is a follow-up to update the scientific community about twin registries around the globe. The present article builds upon our 2013 Registry description by summarizing current information on the Washington State Twin Registry (WSTR), including history and construction methods, member characteristics, available data, and major research goals. We also provide a section with brief summaries of recently completed studies and discuss the future research directions of the WSTR. The Registry has grown in terms of size and scope since 2013; highlights include recruitment of youth pairs under 18 years of age, extensive geocoding work to develop environmental exposures that can be linked to survey and administrative health data such as death records, and expansion of a biobank with specimens collected for genotyping, DNA methylation, and microbiome based-studies.

The Wisconsin Twin Project encompasses nearly 30 years of longitudinal research that spans infancy to early adulthood. The twin sample was recruited from statewide birth records for birth cohorts 1989–2004. We summarize early recruitment, assessment, retention and recently completed twin neuroimaging studies. In addition to the focal twins, longitudinal data were also collected from two parents and nontwin siblings. Our adolescent and young adult neuroimaging sample (N = 600) completed several previous behavioral and environmental assessments, beginning shortly after birth. The extensive phenotyping is meant to support a range of empirical investigations with potentially differing theoretical perspectives.

The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural–geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.