Concerns that comparisons with neighborhood controls might have inadequate power to detect effects on dependence that are shared with both drug exposure and dependence on other substances [e.g., 191 (36%) of the 531 neighborhood controls were dependent on a non-opioid illicit drug; Supplemental Table 1, http://digitalcommons.wustl.edu/psychiatry] prompted a decision to genotype a second, more broadly unaffected control group of unrelated individuals selected from the large Australian Twin Registry (ATR), including twins and family members [see28]. Inclusion criteria were institutional review board approval allowing genotyping of available DNA. Exclusion criteria were lifetime illicit drug or alcohol dependence at the prior interview. Non-nicotine-dependent individuals were preferentially selected; the prevalence of nicotine dependence (12.5%) in ATR controls is below that of the Australian population.
