Finntwin16 (FT16) is a population-based study consisting of five consecutive birth cohorts of twins born between 1975 and 1979 (Kaprio et al., 2002). The five birth cohorts contained 3,065 families of twins in which both twins were living and residing in Finland at the age of 16. Details about data collection have been previously published (Kaprio et al., 2002; Kaprio et al., 2006). All twins were identified through Finland’s Population Register Center, permitting exhaustive and unbiased ascertainment. Zygosity was determined using a well-validated questionnaire completed by both co-twins at the baseline (Kaprio et al., 1991). Here we focus on assessments of alcohol consumption and alcohol problems in young adulthood. The average age for the respondent twins at this assessment was 24.4 years (SD=1.50, range 22.8–27.2), with a response rate of 88.1%. Of these individuals, genotypic data was collected on 602 subjects, 36.0% were monozygotic (MZ) twins (n=216), 63.5% were dizygotic (DZ) twins (n=382). The 602 genotyped individuals were selected from twin pairs extremely discordant and concordant (EDAC selection) for alcohol-related problems, using a 22- item version of the Rutgers Alcohol
