CHRNA5 and nasopharyngeal carcinoma: Furthermore, we examined the joint effect of the CHRNA5 rs3841324 genotype and smoking status on the risk of NPC and found that ever-smokers with the CHRNA5 rs3841324 ins/del or del/del allele had a >4-fold increased risk for NPC (adjusted OR = 4.35; 95% CI, 2.57–7.38) compared with non-smokers homozygous for the ins allele (Table 3).