COGEND was initiated in 2001 as a genetic study of nicotine dependence20,21. Nicotine dependent cases and non-dependent smoking controls were identified and recruited from Detroit and St. Louis. Over 2,900 donated blood samples were collected and used to genotype ~2.5 million SNPs using the HumanOmni2.5 array. After QC, 2,673 subjects were kept for following analyses.
