In an independent sample, the C allele of rs1409568 was also associated with a modest increase in right hippocampal volume (2.13%) but not with cannabis use itself. The hippocampus has been implicated in addiction (47), including volumetric differences that have been observed in chronic cannabis users (14;15). This, in addition to tentative evidence for the role of rs1409568 as a potential enhancer in the middle hippocampus (Figure 2), indicates that this SNP may regulate neural effects that are central to the development of addictions. The lack of association between cannabis use and genotype is not surprising given the vanishingly low number of problem users (e.g., 12 individuals with cannabis abuse) in the DNS sample.
