The gene encoding CB1 (CNR1) is on human chromosome 6q14−15. It is a 25 kb gene with 4 exons, of which the fourth is the largest and most commonly expressed in brain tissue [36]. Tests of association between substance dependence and polymorphisms in CNR1, including SNPs, but also a trinucleotide repeat (AAT)n and an insertion-deletion (−3180T), and have shown conflicting results. As seen in Table 2, several of these studies that used a general measure of substance dependence reported associations with SNPs in CNR1, particularly rs2023239 and rs806368. Another SNP, rs806380 has been implicated in studies of cannabis dependence by Hopfer et al [37] and Agrawal [38] but Herman and colleagues [39] do not report association between polymorphisms in CNR1 and cannabis dependence. In contrast, a majority of the studies of the (AAT)n repeat have yielded negative results [40-42].
