The Finnish Twin Cohort Study

The Finnish Twin Cohort was first established in 1974 to investigate genetic and environmental risk factors for chronic disorders. Twins and their families have been ascertained in three stages from the Central Population Register in 1974 (older like-sexed pairs), 1987 (multiple births 1968-1987) and 1995 (opposite-sex pairs 1938-1957). There are a total of 12,966 MZ and DZ twin pairs (25,932 individuals) with both members currently alive and excluding individuals who refused to participate in studies. The older part consists of same gender twin pairs born before 1958 with both twins alive in 1975 and three surveys have been carried out in 1975, 1981 and 1990 with the response rates varying between 77 and 89%. A fourth survey of the old cohort is ongoing in 2011-2012. A major part of the study information is collected by questionnaires and interviews. This data and registry follow-up has directed many following substudies concentrating more specifically on different phenotypes. In addition to mortality follow-up, morbidity follow-up of the twins has been performed through nationwide computerized medical registries: incident malignancies through the Cancer registry, hospitalizations through the Hospital Discharge Register, disability pension information and information of selected diseases based on the national register for fully-reimbursable medications. Numerous subsample studies have been performed, with DNA collection a routine feature since the mid 1990s. For the younger cohort, two five year birth cohorts born 1975-1979 (Finntwin16) & 1983-1987 (FinnTwin12) have been studied in an intensive longitudinal manner. Together they comprise about 5500 families with twins (twins, parents and sibs), who have participated in five (FinnTwin16, at ages 16, 17 , 18.5, 24 and 35 yrs) or four (FinnTwin12, at ages 11, 14, 17 and 22 yrs) waves of questionnaires & interviews with more intense subset studies, including DNA collection. Among the intensively studies subsamples are studies that have examined pairs and families with obesity, hypertension, smoking, osteoarthritis, migraine, alcohol use, physical inactivity and fitness, dementia, eating disorders, and low back pain risk factors. Over 15000 DNA samples have been collected, and serum and other biological samples are available from several sub-studies as well.

The twin registry includes also information on twin pairs whose MZ/DZ status is unknown/uncertain, older non-like-sexed twin pairs, and twin pairs who have not been actively recruited (born in years 1958-1974 and 1980-1982). [In English] [in Finnish]

University of Helsinki

Principal Investigator: Jaakko Kaprio, firstname.lastname (at)           

Contact: kaksostutkimus (at)

Key references:

Genetic and environmental factors in health-related behaviors: studies on Finnish twins and twin families. Kaprio J, Pulkkinen L, Rose RJ. Twin Res. 2002 Oct;5(5):366-71

Genetic and environmental factors in complex diseases: the older Finnish Twin Cohort. Kaprio J, Koskenvuo M. Twin Res. 2002 Oct;5(5):358-65

Twin studies in Finland 2006. Kaprio J. Twin Res Hum Genet. 2006 Dec;9(6):772-7