About 50–60% of the variance in cannabis use disorders, including DSM-IV dependence, is attributable to the additive effects of genes (i.e., narrow sense heritability)(7). Despite this, only one study to date has successfully identified genomewide significant loci for any cannabis related trait (8). Table 1 provides an overview of six genomewide association studies (GWASs) of cannabis-related phenotypes (9–12), the largest being a recent meta-analysis of GWASs of ever using cannabis, even once during the lifetime (N > 32,000)(13). However, only the recent study by Sherva and colleagues (8) identified genomewide significant loci (three independent regions) for DSM-IV cannabis dependence criterion counts in a sample of European-American (EA) and African-American (AA) descent.
