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 Italian Twin Registry (ITR), established in 2001, is a population-based registry of voluntary twins. To date, it consists of approximately 29,000 twins who gave their consent to participate in the studies proposed by the ITR research group. The database comprises 11,500 monozygotic and 16,700 dizygotic twins resident throughout the country and belonging to a wide age range (from 0 to 95 years, mean 36.8 years). This article provides an overview of the recruitment strategies along with the major phenotypes investigated during an 18 years’ research period. Over the years, several self-reported questionnaire data were collected, together with saliva/blood samples and measurements taken during in-person interviews or outpatient clinical examinations. Mental and behavioral phenotypes as well as atherosclerotic traits were studied in depth across different age groups. A birth cohort of twins was established and followed up. Novel research hypotheses are also being tested in ongoing projects. The ITR is involved in international studies in collaboration with other twin registries and represents a valuable resource for national and international research initiatives regarding a broad spectrum of health-related characteristics.

The Danish Twin Registry (DTR) was established in the 1950s, when twins born from 1870 to 1910 were ascertained, and has since been extended to include twins from birth cohorts until 2009. The DTR currently comprises of more than 175,000 twins from the 140 birth cohorts. This makes the DTR the oldest nationwide twin register and among the largest in the world. The combination of data from several surveys, including biological samples and repeated measurements on the same individuals, and data from Danish national registers provides a unique resource for a wide range of twin studies. This article provides an updated overview of the data in the DTR: First, we provide a summary of the establishment of the register, the different ascertainment methods and the twins included; then follows an overview of major surveys conducted in the DTR since 1994 and a description of the DTR biobank, including a description of the molecular data created so far; finally, a short description is given of the linkage to Danish national registers at Statistics Denmark and some recent examples of studies using the various data resources in the DTR are highlighted.

Twin registers are wonderful research resources for research applications in medical and behavioral genetics, epidemiology, psychology, molecular genetics, and other areas of research. New registers continue to be launched all over the world as researchers from different disciplines recognize the potential to boost and widen their research agenda. In this article, we discuss multiple aspects that need to be taken into account when initiating a register, from its preliminary sketch to its actual development. This encompasses aspects related to the strategic planning and key elements of research designs, promotion and management of a twin register, including recruitment and retaining of twins and family members of twins, phenotyping, database organization, and collaborations between registers. We also present information on questions unique to twin registers and twin-biobanks, such as the assessment of zygosity by SNP arrays, the design of (biomarker) studies involving related participants, and the analyses of clustered data. Altogether, we provide a number of basic guidelines and recommendations for reflection when planning a twin register.

The Avera Twin Register (ATR) aims to study environmental and genetic influences on health and disease using a longitudinal repository of biological specimens, survey data, and health information provided by multiples and their family members. The ATR is located in Sioux Falls, South Dakota, which is a rural and frontier area in the Midwestern United States with a density of four people per square kilometer. The target area of the ATR is South Dakota and the four surrounding states: Minnesota, Iowa, North Dakota, and Nebraska. Enrollment of twins and higher-order multiples of all ages and their family members started on May 18, 2016. A description of the first 13 months of enrollment in this longitudinal register will be provided. The ATR will collect longitudinal data on lifestyle, including diet and activity levels, aging, complex traits, and diseases. Upon registration, all participants are genotyped on the Illumina Global Screening Array (GSA) and twins and higher order multiples receive information on their zygosity. The ATR aims to contribute to large international GWAS consortia and collaborates closely with the Netherlands Twin Register, allowing for the comparison of collected data and analyses of results. In addition, the ATR will address twin-specific questions.

Despite the need to provide evidence-based health policy, most developing countries suffer from a lack of resources for sound epidemiologic evidence. Most twin registers have been established in developed countries and there are relatively fewer twin registers in developing countries. Considering the immense potential of twin research, it will be worthwhile to attempt to establish a new twin register in Mongolia, where biomedical studies are still scarce. Our objectives were to initiate the process of establishing a nation-wide twin register in Mongolia, based on a nation-wide, population-based database. With the approval and support of the Ministry of Population Development and Social Welfare of Mongolia, we were able to access an initial list of 411 twin pairs who live in the district of Ulaanbaatar, the capital city of Mongolia. By developing a questionnaire to estimate zygosity, we conducted a pilot survey. Those who registered consisted of 822 individuals or 411 twin pairs (same sex: male — 178; female — 157; different sex — 76), two sets of triplets (same sex: female — 2). The age of twins ranged from 1 to 81 (mean age 7.3 ± 11.3), and 52.4% were males. The first twin survey in Mongolia not only resulted in interim data for the Mongolian Twin Register, but has the potential for establishing a larger register by using the national database. It has been proven possible to establish a twin register for research purposes in Mongolia.

Over the last 60 years, the resources and the research in the Danish Twin Registry (DTR) have periodically been summarized. Here, we give a short overview of the DTR and a more comprehensive description of new developments in the twenty-first century. First, we outline our experience over the last decade of combining questionnaire and survey data with national demographic, social, and health registers in Statistics Denmark. Second, we describe our most recent data collection effort, which was conducted during the period 2008–2011 and included both in-person assessments of 14,000+ twins born 1931–1969 and sampling of biological material, hereby expanding and consolidating the DTR biobank. Third, two examples of intensively studied twin cohorts are given. The new developments in the DTR in the last decade have facilitated the ongoing research and laid the groundwork for new research directions.

The more that twin and other multiple pregnancies are investigated, the more it becomes mandatory that collaborative studies are set up in order to attain the criticai number of cases needed to achieve meaningful and reliable results. The European Multiple Birth Study (EMBS) aims to study two aspects of twin and multiple pregnancy: 1) management of pregnancy and labour, with emphasis on the prevention of preterm delivery; 2) accurate determination of zygosity, a prerequisite for the proper use of the twin method in a variety of fields, eg, congenital malformations, genetics, clinical investigations, etc. The rationale, the methods and the organisation of the study are described and discussed.

Information about menstrual cycle variables was obtained by questionnaire using 462 female twin pairs. The twins were either members of the Institute of Psychiatry Volunteer Twin Register, or of the Birmingham Population-based Register. The two samples were analysed separately using univariate and multivariate methods so that an independent replication was obtained. Maximum likelihood estimation was used to fit simple models of genetic and environmental variation to these data. The results suggest that age of menarche, menstrual cycle regularity and premenstrual symptom reporting may be heritable, whereas menstrual cycle length is not. The results should be interpreted with caution as not all variables were replicated in the smaller sample, and the method of retrospective menstrual cycle data collection has been questioned.

Previous results regarding a seasonality of twin births have been conflicting. Since the biology of monozygotic (MZ) twinning differs from that of dizygotic (DZ) twinning, it is possible that the seasonality of birth for these two twin types might differ. However, all previous studies examining the seasonality of birth by zygosity has estimated zygosity by Weinberg's method. In this report, the month of birth of all MZ and DZ veteran twins from the United States National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry are compared with that found for an unselected group of veterans. Zygosity in the registry has been individually assigned to all twin pairs by a well-validated method. Compared to unselected veterans, the distribution of births by months did not differ significantly for all the veteran twin pairs or for the MZ and DZ twin pairs considered separately. The distribution of month of birth of the MZ and DZ twin pairs did not differ significantly from one another. These results are not consistent with a significant seasonality of MZ, DZ, or all twin births in the United States.

An obstetric-neonatal-gynecological data bank has been developed for the Aberdeen District in Scotland and is now fully computerized. Within it, a twin register including over 550 pairs of known placentation and zygosity has developed.