Genome-wide linkage studies have identified chromosomal regions that may harbor loci contributing to one of many smoking behavior phenotypes: age at initiation [7], [8]; some variant of CPD [9], [10], [11], [12], [13], [14], [15], [16], [17] DSM-IV Nicotine Dependence [11], [17]; some variant of Ever-Never [9], [17], [18], [19], [20]; Fagerstrom test for nicotine dependence (FTQ, FTND) or Heaviness Smoking Index (HIS) [14], [21], [22]; Pack-years [9], [23]; Current versus Former [11]; and withdrawal severity [11]. While some regions have shown suggestive linkage to smoking behaviors in multiple studies [24], linkage results have generally been heterogeneous and short on conclusive findings; to date no risk loci have been discovered that definitively account for linkage signals.
