For the GWAS sample (described in more detail in Edenberg et al., 2010), unrelated alcohol dependent cases and non-alcohol dependent controls were selected from the pool of alcohol dependent and community-ascertained families. Cases all met DSM-IV criteria for alcohol dependence at some point during their lives. In situations where an alcohol dependent proband had been phenotypically assessed multiple times for their lifetime history, he/she had to have met diagnostic criteria for alcohol dependence at each assessment to be a GWAS “case.” Controls were selected from both the community-recruited families and those recruited through an alcohol dependent individual, but could not share a common ancestor with a case. In addition, controls were required to have consumed alcohol but to have never met criteria for any alcohol-related diagnosis (abuse or dependence). In addition, controls could not have met diagnostic criteria for abuse or dependence of cocaine, stimulants, sedatives, opioids, or marijuana. Because AD is so frequently comorbid with other types of substance dependence, cases meeting diagnostic criteria for other types of dependence were not excluded: 49.9% (N=226) of cases were marijuana dependent;
