Reports suggest that variations in TPH are associated with impulse control problems (New et al., 1998), suicidal behavior (Nielsen et al., 1998), and earlier stages of smoking, such as smoking initiation (Lerman et al., 2001; Sullivan et al., 2001), but not nicotine dependence (Lerman et al., 2001; Sullivan et al., 2001). Three studies have examined polymorphisms within CHRNA10 and smoking related behavior, and found no associations with smoking initiation (Greenbaum et al., 2006), nicotine dependence (Saccone et al., 2007b; Greenbaum et al., 2006), or smoking cessation (Heitjan et al., 2007). The ionotropic kainate glutamate receptor 4 gene (GRIK4), which is located directly under the highest position of the multipoint peak associated with DSM-IV NW in our Australian subsample and in our combined analyses at 123 cM on chromosome 11, was recently found to be associated with response to a selective serotonin reuptake inhibitor (citalopram) used to depressive symptoms (Paddock et al., 2007).
