The FinnTwin12 (FT12) sample includes five birth cohorts of twins born in Finland from 1983 to 1987, identified from national birth records (Kaprio, 2006; Kaprio et al., 2002). These twins have been assessed longitudinally with self-report surveys from age 12 through approximately age 22, and a subset of the epidemiological sample was selected for “intensive” study, receiving in-person clinical assessments at ages 14 and 22. Included in the present study are 1,135 individuals from 652 families in this intensive subset who completed clinical assessments of AUDs at age 22 (M = 22.4, range = 20-26), and who also provided a DNA sample for genotyping. The sample was 53.6% female, with 39.4% monozygotic (MZ) twins, 30.5% same-sex dizygotic (DZ) twins, 29.8% opposite-sex DZ twins, and 0.3% single (unpaired) twins of unconfirmed zygosity.
