for susceptibility genes underlying the transition from regular non-dependent to dependent smokers.49 Weiss et al.51 found a significant association of the cluster with ND only in early-onset smokers. Fourth, other genes in the region, such as a hypothetical locus LOC123688, cannot be excluded because of the association with other SNPs within this cluster.47 However, this issue may be difficult to solve genetically because of the extensive LD structure.
