to conduct genomewide association and rare nonsynonymous variant analyses (McGue et al., 2013; Vrieze et al., 2013a). These studies did not identify any single common or rare variant at a genomewide significant level; however, the authors reported that 84% of the heritability in illicit drug use was explained by both common and rare variants. While the work of McGue and colleagues included multiple measures of nicotine use and dependence, we elected to exclude nicotine from these measures of general liability based on the work by Kendler and colleagues (Kendler et al., 2007), which showed significant drug-specific genetic influences on nicotine dependence.
