The Genesis 12–19 (G1219) Study is an ongoing longitudinal study of a sample of UK twin pairs, non-twin sibling pairs, and their parents. G1219 was initially designed to examine the role of gene–environment interplay in adolescent depression. However, since then data have continued to be collected from both parents and their offspring into young adulthood. This has allowed for longitudinal analyses of depression and has enabled researchers to investigate multiple phenotypes and to ask questions about intermediate mechanisms. The study has primarily focused on emotional development, particularly depression and anxiety, which have been assessed at multiple levels of analysis (symptoms, cognitions, and relevant environmental experiences). G1219 has also included assessment of a broader range of psychological phenotypes ranging from antisocial behaviors and substance use to sleep difficulties, in addition to multiple aspects of the environment. DNA has also been collected. The first wave of data collection began in the year 1999 and the fifth wave of data collection will be complete before the end of 2012. In this article, we describe the sample, data collection, and measures used. We also summarize some of the key findings to date.

TwinsUK is a nation-wide registry of volunteer twins in the United Kingdom, with about 12,000 registered twins (83% female, equal number of monozygotic and dizygotic twins, predominantly middle-aged and older). Over the last 20 years, questionnaire and blood/urine/tissue samples have been collected on over 7,000 subjects, as well as three comprehensive phenotyping assessments in the clinical facilities of the Department of Twin Research and Genetic Epidemiology, King's College London. The primary focus of study has been the genetic basis of healthy aging process and complex diseases, including cardiovascular, metabolic, musculoskeletal, and ophthalmologic disorders. Alongside the detailed clinical, biochemical, behavioral, and socio-economic characterization of the study population, the major strength of TwinsUK is availability of several ‘omics’ technologies for the participants. These include genome-wide scans of single nucleotide variants, next-generation sequencing, exome sequencing, epigenetic markers (MeDIP sequencing), gene expression arrays and RNA sequencing, telomere length measures, metabolomic profiles, and gut flora microbiomics. The scientific community now can freely access parts of the phenotype data from the ‘TwinsUK’, and interested researchers are encouraged to contact us via our Web site (www.twinsuk.ac.uk) for future collaborations.

The Genetics of Sexuality and Aggression (GSA) project was launched at the Abo Akademi University in Turku, Finland in 2005 and has so far undertaken two major population-based data collections involving twins and siblings of twins. To date, it consists of about 14,000 individuals (including 1,147 informative monozygotic twin pairs, 1,042 informative same-sex dizygotic twin pairs, 741 informative opposite-sex dizygotic twin pairs). Participants have been recruited through the Central Population Registry of Finland and were 18–49 years of age at the time of the data collections. Saliva samples for DNA genotyping (n = 4,278) and testosterone analyses (n = 1,168) were collected in 2006. The primary focus of the data collections has been on sexuality (both sexual functioning and sexual behavior) and aggressive behavior. This paper provides an overview of the data collections as well as an outline of the phenotypes and biological data assembled within the project. A detailed overview of publications can be found at the project's Web site: http://www.cebg.fi/.

In 2002 and 2006, review papers have described the Finnish Twin Cohort and studies conducted on these population-based, longitudinal data sets with extensive follow-up data. Three cohorts have been established: the older twin cohort in the 1970s, and the Finntwin12 and Finntwin16 studies initiated in the 1990s. The present review provides on update on the latest data collections conducted since the previous review. These cover the fourth waves of data collection in the older cohort (twins born before 1958) and Finntwin12 (twins born 1983–1987). The fifth wave of data collection in Finntwin16 (twins born 1975–1979) also included assessments of their spouses/partners. An analysis of mortality in the older cohort from 1975 to 2009 indicates that the mortality of adult twins (as individuals) does not differ from the population at large. Based on the cohorts, many sub-studies with more detailed phenotyping and collection of omics data have been conducted or are in progress. We also contribute to numerous national and international collaborations.

The Berlin Twin Registry has its focus on health research. It is operated as a private company, making twin studies available to academic institutions as well as commercial partners in the area of biotechnology and nutrition. Recruitment is based on invitation in the context of mass media coverage of scientific results. Phenotyping in the unselected twin subjects is directed toward intermediate phenotypes that can bear on common diseases. These phenotypes include proteomic approaches and gene expression. Some results are briefly described to give an impression of the range of research topics and related opportunities for retrospective and prospective collaborative research.

The Bielefeld Longitudinal Study of Adult Twins (BiLSAT) is a German longitudinal study of monozygotic and dizygotic twins reared together, including more than 1,100 twin pairs aged between 14 and 80 who participated in the first wave. Data were collected at five waves of assessment between 1993 and 2009. Initially, the study focused on genetic and environmental influences on the structure and the development in adult temperament and personality. Today, the study includes a broad range of individual variables, such as personality disorders, major life goals, interests, attitudes, values, life and work satisfaction, and major life events. A special feature of this genetically informative study lies in the multiple-rater approach (i.e., self-reports and peer reports). Longitudinal multiple-rater analyses allow researchers to go beyond the basic nature–nurture decomposition of variance in self-reports examining genetic and environmental influences on stability and change in more accurately measured individual attributes. In the current article, we briefly describe the design and contents of BiLSAT as well as some recent major findings and future plans.

This article summarizes the status of three recent German twin studies: CoSMoS, SOEP, and ChronoS. The German twin study on Cognitive Ability, Self-Reported Motivation, and School Achievement (CoSMoS) is a three-wave longitudinal study of monozygotic and dizygotic twins reared together, and aims to investigate predictors of and influences on school performance. In the first wave of the data collection in 2005, 408 pairs of twins aged between 7 and 11 as well as their parents participated in CoSMoS. The SOEP twin study is an extended twin study, which has combined data from monozygotic and dizygotic twins reared together with additional data from full sibling pairs, mother–child, and grandparent–child dyads who participated in the German Socio-Economic Panel (GSOEP) study. The SOEP twin project comprises about 350 twin and 950 non-twin pairs aged between 17 and 70. Data were collected between 2009 and 2010, with a focus on personality traits, wellbeing, education, employment, income, living situation, life-satisfaction, and several attitudes. The aim of the Chronotype twin study (ChronoS) was to examine genetic and environmental influences on chronotype (morningness and eveningness), coping strategies, and several aspects of the previous SOEP twin project in a sample of 301 twin pairs aged between 19 and 76 years, recruited in 2010 and 2011. Part of the ChronoS twin sample also participated in the earlier SOEP twin study, representing a second wave of assessments. We briefly describe the design and contents of these three studies as well as selected recent findings.

Twins traditionally retain a special status in many African societies. In Guinea-Bissau, twins are often well regarded yet still suffer from a very high mortality, especially in the perinatal and infant period. At the Bandim Health Project, a health and demographic surveillance site, we have recently established one of the first twin registries in Sub-Saharan Africa. Our short-term aim is to describe twin mortality and morbidity in order to design appropriate health interventions. Our long-term goal is a large-scale database to explore the pathogenesis of prevalent diseases; for example, diabetes mellitus, metabolic syndrome, and infectious diseases such as HIV, tuberculosis, and malaria. A major focus area is also the etiology of low birth weight and how epigenetic processes might modulate the consequences of low birth weight in Sub-Saharan Africa. For this, monozygotic twin studies represent a powerful tool. Though twin studies have been carried out by the Bandim Health Project for more than 30 years, the renewed registry described here was officially established in 2009 and includes both a cohort of newborn twins and a cohort of young and adult twins. Currently more than 1,500 twins are being followed in the two cohorts combined. We believe that the registry holds exciting possibilities and will encourage the establishment of further twin registries across the region.

The first Hungarian Twin Registry was established in Budapest in 1970 through the mandatory reporting of multiple-births. In the 1980s a second, volunteer adult registry was also founded. Unfortunately, both registries ceased to exist in the 1990s. Efforts started in 2006 to revive a Hungarian twin registry. The team spearheading this effort reports here on this progress. Currently, the voluntary Hungarian Twin Registry consists of 310 adult twin pairs and multiplets. Current research focuses on cardiovascular and respiratory health and yielded multiple awards and publications. Efforts are on the way to expand into social, psychological, and obesity studies.

The Italian Twin Register has been in place for more than 10 years. Since its establishment, it has been focusing, on the one hand, on a continuous update of the existing information, and on the other hand, on new phenotypes and sample collection. Demographic data on about 140,000 twins have been updated using the municipality registries. The Italian Twin Register has been carrying out several new studies during the last few years. A birth cohort of twins, Multiple Births Cohort Study, has been started and the enrolment is ongoing. For this cohort, data on pregnancy and birth are collected, and periodical follow-ups are made. DNA is being collected for the twins and their parents. In the area of behavioral genetics, most efforts have been directed to psychological well being assessed with self-reported tools. Research on age-related traits continues with studies on arteriosclerosis development, early biomarkers in mild cognitive impairment, and the relation between lifestyle habits and mutagen sensitivity. The Italian Twin Register biobanking has grown in its size and in its know-how in terms of both technical issues and ethical procedures implementation. Furthermore, attitudes toward biobank-based research, together with willingness and motivation for donation, are being investigated. A valuable key resource for the Italian Twin Register is the possibility of linking twin data with disease registries. This approach has been yielding several important results, such as the recent study on the heritability of type 1 diabetes.

The Longitudinal Israeli Study of Twins (LIST) is a social developmental study, which implements social-developmental, molecular genetic, epigenetic, and behavioral genetic methods to advance knowledge on the development of individual differences in social behavior. Twins are followed from the age of three and both observational and parental-questionnaire data are collected on their empathy, temperament, and pro-social behavior. The parenting styles of parents are also evaluated using self-reports and observations and DNA samples are collected from parents and twins. In the current paper, we provide a review of our recent work and discuss the future aims of the LIST.

The Keio Twin Research Center has conducted two longitudinal twin cohort projects and has collected three independent and anonymous twin data sets for studies of phenotypes related to psychological, socio-economic, and mental health factors. The Keio Twin Study has examined adolescent and adult cohorts, with a total of over 2,400 pairs of twins and their parents. DNA samples are available for approximately 600 of these twin pairs. The Tokyo Twin Cohort Project has followed a total of 1,600 twin pairs from infancy to early childhood. The large-scale cross-sectional twin study (CROSS) has collected data from over 4,000 twin pairs, from 3 to 26 years of age, and from two high school twin cohorts containing a total of 1,000 pairs of twins. These data sets of anonymous twin studies have mainly targeted academic performance, attitude, and social environment. The present article introduces the research designs and major findings of our center, such as genetic structures of cognitive abilities, personality traits, and academic performances, developmental effects of genes and environment on attitude, socio-cognitive ability and parenting, genes x environment interaction on attitude and conduct problem, and statistical methodological challenges and so on. We discuss the challenges in conducting twin research in Japan.

Osaka University Center for Twin Research is currently organizing a government-funded, multidisciplinary research project using a large registry of aged twins living in Japan. The purpose of the project is to collect various information as well as biological resources from registered twins, and to establish a biobank and databases for preserving and managing these data and resources. The Center is collecting data from twin pairs, both of whom have agreed to participate in a one-day comprehensive medical examination. The following data are being collected: physical data (e.g., height, body mass, blood pressure, theoretical visceral fat, pulse wave velocity, and bone density), data regarding epidemiology (e.g., medical history, lifestyle, quality of life, mood status, cognitive function, and nutrition), electrocardiogram, ultrasonography (carotid artery and thyroid), dentistry, plastic surgery, positron emission tomography, magnetoencephalogram, and magnetic resonance imaging of brain. These data are then aggregated and systematically stored in specific databases. In addition, peripheral blood is obtained from the participants, and then genomic DNA is purified and sera are stored. A wide variety of studies are ongoing, and more are in the planning stage.

To gain widespread participation, epidemiologic studies of twins from pregnancy through the childhood period are expected to reflect the needs and concerns of families and provide participants with appropriate and useful feedback based on scientific evidence. Our most recent database on families with twins throughout Japan is based on a questionnaire survey conducted from January 2010 to August 2011. Mailed or hand-delivered questionnaires, consisting of over 550 items were used to collect the basic data. The response rate was 40% (956/2,401). This is part of a nation-wide study designed to assess the long-term effect of perinatal conditions on mothers of multiples. Its aim was to study the growth and development of multiples in childhood, and to conduct a genetic epidemiologic study to test the developmental origin of health and disease hypothesis. One of the ultimate aims of this research was to provide evidence-based information on parenting multiples from pregnancy through childhood to families with multiples.

This article profiles the historical twin databases of the secondary education school attached to the Faculty of Education at the University of Tokyo. The school was established in 1948. Every year, about 50 pairs of twins of all sex and zygosity combinations and aged 11–12 years take an examination, and about 10–20 pairs are admitted based on the results. Three data sets exist: one for applicants (11–12 years), one for junior and senior high school students (12–18 years), and one for graduates (18–79 years). Record linkage of these three databases should facilitate several important research projects; for example, the lifecourse genetic epidemiologic studies and verification of so-called developmental origin of health and disease hypothesis.