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For the Danish Twin Registry (DTR) to maintain a position among the leading genetic-epidemiological registries in the world, the DTR Infrastructure Project (DTRIP) was funded by the Ministry of Science, Technology and Innovation. The project was launched in 2008 and the survey part of the project closed just before Christmas 2011. The DTRIP is the umbrella project for a number of subprojects that together comprise the assessment and sampling of biological material from approximately 14,000 MZ and DZ twins. The aims of the project were to extend and consolidate the infrastructure in the Registry, and in addition to collect biological material on the midlife cohorts of the Registry.


The DTRIP was organized in a number of subprojects. The most notable are: a) The Middle Aged Danish Twin Follow-Up (MADT-FU) survey which is a follow-up of the 4,314 twins who participated in a major study in 1998, b) The MiDT study which is the non-MADT twin population born 1931-1969 that we were not able to include in 1998, c) The Life Span Study of 150 MZ, birth weight-discordant twin pairs and d) The Geminakar II Survey which is a longitudinal twin study of the impact of genes and environment on insulin resistance, obesity and CVD risk factors.


A coordination center and a database were established at DTR to keep track of all the mailings, consents and bookings at the different assessment centers throughout Denmark. Persons giving their active, written confirmation to participate in the project were subsequently contacted by phone for additional information and an appointment was made in the study management system. The DTRIP was organized in collaboration with 5 assessment centers throughout the country located in Copenhagen, Aarhus, Odense, Aalborg and Kolding. Twins who were not able to come to one of the assessment centers due to health problems or were living on distant islands or places were offered the possibility to participate in an in-home interview and examination instead. All interviewers had a medical background and received a standardized training program in advance to study debut, and quality assurance checks were performed throughout the enrollment period.  All survey data from the questionnaires were scanned, verified, cleaned and stored in the DTR databank. Blood samples were spun, fractionated and stored in -80oC freezers in the DTR biobank.


Whichever site for examination and to maximize comparability with former surveys all participants completed an identical assessment: a) A mail survey consisting of approximately 100 questions, b) The completion of an 1-hour, in-person interview and examination and c) Provision of a blood sample for DNA analysis and other biological assays.

Mail survey

Socio demographic information (marital status, children, housing situation, education, work and employment), health-related variables (self-rated health, pulmonary health, diseases and symptoms, vision and hearing). Psychological well-being (CAMDEX), lifestyle and health habits, vitamin C intake, alcohol and tobacco consumption, exercise and physical, intellectual, cultural and social activities.

1-hour assessment

Medication inventory, blood pressure measurement, grip strength measurement, repeated chair-stand test, anthropometric measures (height, weight, waist), spirometry, and neurocognitive testing (12-word recall immediate and delayed), digit-symbol substitution task, digit span forward and backward, and verbal fluency (kinds of animals).

Biological sample:

A 30 mL blood sample was drawn for future DNA extraction and measurement of various biological variables.


The incorporation of biological specimens for the midlife cohorts of the Registry with the extensive clinical and lifestyle data provides us with a unique opportunity to a) explore the interaction of genes and environment in aging, b) study the etiology of late-life diseases, c) learn about midlife phenotypes and to follow the aging and disease processes, d) help us address the public health needs of the next generation of elderly, e) identify the genetic basis of common medical conditions, f) find epigenetic contributions to disease risk, and g) characterize gene-environment interactions in disease etiology.

Selected publications

The Danish Twin Registry: Linking surveys, national registers, and biological information.
Skytthe A, Christiansen L, Kyvik KO, Bødker FL, Hvidberg L, Petersen I, Nielsen MM, Bingley P, Hjelmborg J, Tan Q, Holm NV, Vaupel JW, McGue M, Christensen K.Twin Res Hum Genet. 2013 Feb;16(1):104-11. Pubmed abstract