rs4953

This population-based study examined natural selection on nicotinic receptor gene clusters (CHRNB3-A6 on chromosome 8 and CHRNA5-A3-B4 on chromosome 15) using 1000 Genomes data from three populations. Using Tajima's D and integrated haplotype score (iHS) tests, the authors found strong evidence for positive selection in the CHRNB3-A6 region and moderate evidence in CHRNA5-A3-B4. These regions harbor variants previously associated with nicotine dependence (rs16969968, rs1451240) and cocaine dependence. To understand the target of selection, the authors tested variants in COGA subjects (N=492) for association with cognitive phenotypes (WAIS tests) and found one significant association: rs7017612 with WAIS Digit Symbol score (β=0.43, p=0.003), suggesting memory and learning may be the driving force behind selection.

This Bayesian pharmacogenetic analysis of a bupropion vs placebo smoking cessation trial (n=436 European ancestry participants) identified four SNPs with pharmacogenetic relevance from 59 candidate SNPs in nicotinic acetylcholine receptor genes. The strongest signal was rs871058 in CHRNA5, which showed treatment-by-SNP interaction effects on 7-day smoking cessation rates. Bayesian hypothesis testing proved more conservative than unadjusted frequentist tests but less so than multiplicity-corrected tests, with no control SNPs showing significant associations.