FinnTwin16 is a population–based longitudinal study of five consecutive birth cohorts (1975–1979) of Finnish twins and their families [25, 26]. Initially, 3065 families (6130 twins) were contacted, with a 91% response rate. Questionnaire assessments including detailed alcohol and smoking data were conducted on twins as they reached the ages of 16, 17, 18½, and young adulthood (ages 22–25). For an intensive study on predictors of alcoholism, both twin pairs with very similar alcohol use and twin pairs with dissimilar alcohol use were identified [27, 28]. Additionally, some randomly picked twin pairs functioning as a control group were selected. The 602 subjects of the intensive sample have DNA and serum available. Among this sample, cotinine and 3-hydroxycotinine were measured from all self-identified current smokers, and 174 subjects (40 MZ individuals (one co-twin from each MZ pair), 76 DZ individuals from 38 full DZ pairs, and additional 58 DZ individuals (one co-twin from each DZ pair)) with cotinine above 10ng/ml and 1000Genomes imputed genome-wide genotype data available were included in the NMR GWAS analyses. Genome-wide Infinium 450k Methylation BeadChip data (from whole blood DNA) were available on 14 of the NMR GWAS subjects.
