Several studies suggest that there is a moderate genetic influence on cannabis dependence, and recently there have been additional reports that have identified regions in the genome that may be linked to cannabis dependence [see Kendler and Prescott, 1998; Tsuang et al., 1998; Maes et al., 1999; Miles et al., 2001; Lynskey et al., 2002; Kendler et al., 2003; Rhee et al., 2003; Wilhelmsen and Ehlers, 2005; Agrawal and Lynskey, 2006; Hopfer et al., 2007; Agrawal et al., 2008a,b]. Only two sites, one on chromosome 1 and one on chromosome 2, were identified in the present study for DSM-IV cannabis dependence. The site on chromosome 1 at 154 cM (LOD = 2.1) does not appear to be within 30 cM of other sites identified using substance dependence phenotypes. However, this peak was between two sites; one at around 197 cM that was identified by Dick et al. [2002] in the Collaborative Study for the Genetics of Alcoholism (COGA) dataset for a quantitative alcohol-related phenotype and one at around 102 cM for a cannabis problems factor score in an autosomal linkage scan for cannabis use disorders in the nicotine addiction genetics project [Agrawal et al, 2008a].
