Genomics and personalized medicine: CHRNA5- CHRNA3-CHRNB4 and smoking cessation treatment

Cigarette smoking is highly addictive, and modern genetic research has identified robust genetic influences on nicotine dependence. An important step in translating these genetic findings is to identify the genetic factors affecting smoking cessation in order to enhance current smoking cessation treatments. We review the significance of variants in the nicotinic receptor gene cluster (CHRNA5eCHRNA3eCHRNB4) in the prediction of smoking quantity, smoking cessation, and response to cessation medication in multiple studies of smoking cessation. Three common haplotypes (low-risk, intermediate-risk, and high-risk) in the CHRNA5eCHRNA3eCHRNB4 region are defined by rs16969968 and rs680244. The genetic variants in the CHRNA5eCHRNA3eCHRNB4 region that predict nicotine dependence also predicted a later age of smoking cessation in a community-based sample. In a smoking cessation trial, these variants predicted abstinence at the end of treatment in individuals receiving placebo medication, but not among individuals receiving active medication. Pharmacological treatments moderate the genetic risk in affecting cessation success. These pharmacogenetic interactions have been reproduced by a recent meta-analysis of smoking cessation trials. The number needed to treat was four for smokers with the highrisk haplotype, seven for smokers with the intermediate-risk haplotype, and > 1000 for smokers with the low-risk haplotype. The wide variation in number needed to treat between smokers with different haplotypes supports the notion that personalized smoking cessation intervention based upon genotype could meaningfully increase the efficiency of such treatment. In summary, variants in the CHRNA5eCHRNA3eCHRNB4 region identify individuals at increased risk of cessation failure, and this increased risk can be ameliorated by cessation pharmacotherapy.