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Twin Registers: The Danish Twin Registry

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  1. Twin Registers:The Danish Twin Registry Axel Skytthe, Institute of Pubic Health, University of Southern Denmark

  2. Twin Registers • Collection of individuals from multiple births … • Register: • Longitudinal dimension - maintenance • Continuedfollow-up • Big numbers … • Purpose: • Provide basis for studies to disentangle the importance of genetic, familial and environmental factors on life events, health conditions and diseases

  3. Types of Twin Registers • Local registers vs. national registers • Specific vs. general • Focus on a specific phenotype • Wide range of phenotypes • Population-based vs. Disease-based

  4. Ascertainment • Identification methods • Self-reported • Advertisments • Hospital-based • Medical birth records • Population registers • Follow up / Tracing • Population registers • Death registers • Relatives • Probate court

  5. Twin Registers - Examples • Nordic twin registers • Sweden • Established in late 1950’s • Birth cohorts 1886-2008 • Approx. 97,000 twin pairs • Norway • 3 separate twin cohorts compiled at different research institutions, and each compiled with specific research agendas • Birth cohorts from 1895-1960 and 1967- • Approx. 67,000 twin pairs • Not consistently followed up • Finland • First cohort established 1975 from Central population register • Approx. 65,000 twin pairs

  6. Twin Registers - Examples • European • Sct Thomas, UK • Established 1990 • Volunteers • Focused on diseases occuring in women -> predominantly same-sexed female twin pairs • The Netherlands Twin Register • Established 1986 • Predominantly young twins registered at birth • Includes other family members as well • Approx. 30,000 win pairs • East Flandern Prospective Twin Survey • Initiated in 1964 • Registered at birth – collection of data related to twin maternities • Approx 7,000 twin pairs • Italian Twin Register • Initiated 1996 as a register of ”possible twins” – 600,000 pairs • Enrolled approx. 4,500 twin pairs

  7. Twin Registers - Examples • Outside Europe • NAS-NRC Twin Registry of WWII Military Veteran Twins • Established in 1960’s • Only white male-male twin pairs – 16,000 twin pairs • Born 1917-1927 • Both served in the armed forces • Minnesota Twin Registry (USA) • Established in 1983 • Birth record based … • Vietnam Era Twin Registry (USA) • Established mid 1980’s • Only male-male twin pairs – 7,369 twin pairs • Both serving in the military during 1965-1975 • Identification based on miltary records

  8. Danish Twin Registry (DTR) – Old Cohorts Local vicars searched births registers and reported twins

  9. DTR – Old Cohorts Local vicars searched birth registers and reported twins Twins were traced through municipial population registers, death registers, probate courts, family members Period: 1954 - 1979

  10. The Old Core of DTR

  11. The Old Core ...

  12. Data processing...

  13. DTR – Young Cohorts Identified and traced through the national Civil Registration System Selection criteria: Children of mothers giving birth to more than one child within 3 days Period: 1991-1992

  14. DTR – Young Cohorts

  15. DTR – Middle Cohorts Mainly identified and traced through the CRS, followed by questionnaire of twin status Selection criteria: Persons born the same day and same place, and given the same surname at birth Period: 1996-1998

  16. DTR – Child Cohorts Identified through the Medical Birth Registry as all multiple births Traced through CRS Period: 2001-2010

  17. DTR – Number of Twin Pairs - Gender # Twin pairs born outside Denmark are included in DTR (678 twin pairs) § In addition 775 triplets and 22 quadruplets are included in DTR

  18. Assesment of Zygosity • Questionnaire method • Similarity questions: • 1. Do you and your twin look - like two ordinary siblings? - like two peas in a pod? - not very much alike? • 2. In school, is/was it difficult for your teachers and friends to tell you apart? • 3. Is/was it difficult for your family and friends to tell you apart? • 4. In childhood, did you and your twin have both the same eye color and the same hair color? • Biological material • Serological markers • Genetic markers

  19. Zygosity Assesment - Accuracy Christiansen et al., Twin Res 2003;6:275-278

  20. Zygosity Assesment - Accuracy Christiansen et al., Twin Res 2003;6:275-278

  21. DTR – Number of Twin Pairs - Zygosity # Twin pairs born outside Denmark are included in DTR (678 twin pairs) § In addition 775 triplets and 22 quadruplets are included in DTR

  22. Basic Data • Core data • Identification • Gender • Date of birth, place of birth • Name & address • Vital status (incl. date of death, emigration) • Protection status • Zygosity

  23. DTR – Present Core Data Structure • Parent-Child • P-Id • C-Id • Type (biol/legal) • Ascertainment • Method • Date of Ascert • Spouse • Sp-Id • Marital status • Date of M.St. • Person • Id • PNR • Date of Birth • Gender • Name • Address • Vital status • Date of Vital st. • Access • Pair • Pair-Id • Tw1-Id • Tw2-Id • Type • Zygosity • Pair-Id • Zygosity • Method • Date of assessment

  24. Additional Data • Test results (performance tests, physical, cognitive) • Family (Spouse(s), Parents, Children) • Biological material • Blood spots on filter paper • Full blood samples • Cheek swab • Hair • Pictures

  25. Surveys • Questionnaire surveys • Large scale self-administered questionnaire surveys (1966, 1994, 2002, 2003) • Interview-based surveys (LSADT 1995-2005, MADT 1998) • Disease-specific surveys • Asthma • Low back pain • Epilepsy • Arthritis • Clinical studies • GEMINAKAR – 1 day test program (e.g. oral glucose test, fat tolerance test, fitness, EKG, BP, blood samples, etc)

  26. Middle-aged Twins 2008 • Biobank with samples from 13,000 twins • Collection period 2008-2011 • Birth cohorts 1931-1969 • Full blood samples • Short questionnaire • Life style • Health problems • Medicine • SES • Physical and cognitive performance • Height, weight

  27. Data from National Registers Requirement: Unique Personal Identification Number (PIN) used in all registers

  28. Linkage to Databases and Registers • Registration unit of database? • Hospital discharge register: • Admissions • Diagnoses • Operational procedures • Organisation of database? • Cross-sectional vs. longitudinal • Truncation? • Which period is covered by database? • Studybase? • Both twins should be at risk

  29. Twins and Register-based Research • Advantages • Data exist • Big numbers • No dropout • No bias • Population-based • Caution • Zygosity needed • Not all phenotypes available • Administrative registers – not always suited for research