rs1317286

This pharmacogenetic study of 52 healthy nonsmoking volunteers demonstrates that the effect of nicotine on prepulse inhibition (a measure of sensorimotor gating) is modulated by the CHRNA3 rs1051730 polymorphism. Nicotine significantly enhanced PPI in TT homozygotes (p=0.03) but tended to worsen PPI in TC and CC carriers (p=0.16-0.28). The findings suggest that individuals carrying the nicotine dependence risk allele (T allele) may be more susceptible to neurocognitive enhancement from nicotine, potentially contributing to addiction vulnerability.

Family-based association analysis of 22 SNPs in the CHRNA5/CHRNA3/CHRNB4 gene cluster on chromosome 15 with nicotine dependence in African Americans (N=1053) and European Americans (N=515). Individual SNP analyses showed nominal associations for rs1317286 and rs8040868 in CHRNA3 with smoking quantity and Heaviness Smoking Index (P=0.017–0.05), though none survived correction for multiple testing. Haplotype analysis identified significant associations with nicotine dependence measures before correction in both ethnic groups. Gene-gene interaction analysis using pedigree-based generalized multifactor dimensionality reduction detected significant interactions within CHRNA3 and among all three genes in African Americans and combined samples (P=0.002–0.045).

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 comprehensive association study of 226 SNPs across all 16 nicotinic receptor subunit (CHRN) genes identified four distinct genetic loci significantly associated with nicotine dependence in 1050 cases and 879 controls of European descent. The two most significant associations were rs16969968 (CHRNA5, non-synonymous, p=0.00013, OR=1.30) and rs578776 (CHRNA3, p=0.00011, OR=1.34) in the CHRNA5-CHRNA3-CHRNB4 cluster; one locus in the CHRNB3-CHRNA6 cluster tagged by rs13277254 (p=0.00010); and a novel locus in the CHRND-CHRNG cluster tagged by rs12466358 (p=0.00027). Joint analyses confirmed statistical independence of the two CHRNA5-CHRNA3-CHRNB4 signals.