The two CHRNA4 SNPs implicated in this study with ND symptoms have been implicated previously in smoking related phenotypes. rs1044396 has been nominally associated with nicotine addiction, ND, heavy and regular smoking versus control, and smoking quantity (Breitling et al. 2009; Feng et al. 2004b; Li et al. 2005), although a recent study found no association between this SNP and smoking status (Tsai et al. 2012). Together with the data presented here, there are now three studies showing evidence that the minor allele of rs1044396 increases the risk of ND (Breitling et al. 2009; Feng et al. 2004b).
