The older Finnish Twin Cohort was established in 1974, to include same-sexed twins born before 1958 and with both twins alive in 1975. The baseline survey in 1975 and a first follow-up in 1981 was sent to all available twins. In 1990, the third follow-up health survey was restricted to twins born 1930-1957. The fourth wave of assessments was done in three parts, with a questionnaire study of twins born 1945-1957 in 2011-2012, while older twins were interviewed and screened for dementia in two time periods, between 1999 and 2007 for twins born before 1938, and between 2013 and 2017 for twins born 1938-1944.
The content of these four waves of assessments is described on our website and some recent results are in our recent review (Kaprio et al, 2019). In addition, we have invited twin pairs, based on response to the cohort-wide surveys, to participate in multiple detailed in-person studies. In 2018 biosamples of the twins have been biobanked in the national THL Biobank.
FinnTwin12 (FT12) was designed as a 2-stage study. In the first stage, we conducted multi-wave questionnaire research enrolling all eligible twins born in Finland during 1983-87 along with their biological parents. In stage 2, we intensively studied a subset of these twins with in-school assessments at age 12 and semi-structured poly-diagnostic interviews at age 14. At baseline, parents of intensively studied twins were administered the adult version of the interview. Laboratory studies with repeat interviews, neuropsychological tests, and collection of blood sample or saliva for DNA were made of intensively-studied twins during follow-up in early adulthood.
Genotyping, methylation analysies and metabolomics have been done. A basic aim of the FT12 study design was to obtain information on individual, familial and school/neighborhood risks for substance use/abuse prior to the onset of regular tobacco and alcohol use, to then track trajectories of use and abuse and their consequences into adulthood. But the longitudinal assessments were not narrowly limited to this basic aim, and with multi-wave, multi-rater assessments from ages 11-12, the study has created a richly informative data set for analyses of gene-environment interactions of both candidate genes and genome-wide measures with measured risk-relevant environments.
For details, please see our twinstudy website and the recent review: Rose RJ, Salvatore JE, Aaltonen S, Barr PB, Bogl LH, Byers HA, Heikkilä K, Korhonen T, Latvala A, Palviainen T, Ranjit A, Whipp AM, Pulkkinen L, Dick DM, Kaprio J. FinnTwin12 Cohort: An Updated Review. Twin Res Hum Genet. 2019 Oct ;22(5):302-311.
FinnTwin16 was initiated in 1991 to identify the genetic and environmental precursors of alcohol use, alcohol abuse and alcoholism. Families with twins born 1975-1979 were invited to participate, with baseline data collection by mailed questionnaire from both parents, the twins and siblings. The first survey was done when the twins turned 16 years of age. To date, five waves of data collection have been completed (at ages 16, 17, 18.5 in adolescence, and at average age 24 and 34 in young and early mid-adulthood).
The scope of the project has included studying the determinants of various health-related behaviors and diseases in different stages of life. The main areas addressed are alcohol use and its consequences, smoking, physical activity, overall physical health, eating behaviors and eating disorders, weight development, obesity, life satisfaction and personality. Several sub-studies with more detailed phenotyping and collection of omics data are completed or underway.