A Genome-Wide Association Study of Nausea Incidence in Varenicline-Treated Cigarette Smokers

Sex dependent genetic architecture of biochemically verified tobacco use

BACKGROUND

Tobacco use differs by genetics and sex, and dose-dependently increases the risk for numerous diseases. Nicotine is metabolized to cotinine (COT) which is further metabolized to 3'hydroxycotinine (3HC). COT and COT+3HC are biomarkers which capture tobacco intake more accurately than self-reported measures such as cigarettes/day. It is currently not known whether genetic risk factors for heavier tobacco intake, measured using these biomarkers, differ by sex.

METHODS

We conducted a genome-wide genotype-by-sex (GxS) interaction analysis of COT and COT+3HC measured from blood in European treatment-seeking smokers (n = 541 males, n = 389 females) (NCT01314001). Linear regression models included Genotypes (coded additively), Sex, a GxS interaction term, covariates, and all covariate-by-genotype and covariate-by-sex interaction terms.

RESULTS

For COT, five suggestive (P < 5 × 10-6) loci on chr 4, 15, 19, 12, and 1 were identified; the top variant was rs11520555 (5' of SPOCK3; beta=0.38, se=0.08, GxS P = 7.39 × 10-7). For COT+3HC, eight suggestive loci on chr 21, 18, 17 (2 loci), 13, 5, 8, and 19 were identified; the top variant was rs73157714 (3' of HSPA13; beta=0.33, se=0.06, GxS P = 3.48 × 10-7). Overall, 26 genes were mapped, with 9 showing moderate to high expression in brain, and 5 showing prior associations with psychiatric traits in the GWAS Catalog.

CONCLUSIONS

Our findings suggest that the genetic architecture of tobacco intake, measured accurately using biomarkers, differs between women and men. A more granular understanding of factors influencing tobacco intake in women versus men may identify risk factors for heavier use and sex-specific opportunities to promote smoking cessation and mitigate disease risk.

IMPLICATIONS

This genome-wide interaction study suggested that some of the genetic influences on tobacco intake, measured accurately using biomarkers, differ by sex. The loci identified in our study could be a starting point for developing new genetic biomarkers that predict sex-specific differences in tobacco intake and disease risk.

Genetic Prediction of Smoking Cessation Medication Side Effects: A Genome-Wide Investigation of Abnormal Dreams on Varenicline

Varenicline, the most efficacious smoking cessation monotherapy, produces abnormal dreams. Although genetic contributions to varenicline-associated nausea and cessation have been identified, the role of genetics in abnormal dreams is unknown. We conducted a genomewide association study (GWAS) of abnormal dreams in 188 European ancestry smokers treated with varenicline (NCT01314001). Additive genetic models examined the likelihood of experiencing abnormal dreams 2 weeks following varenicline initiation. For the top locus, we tested for selectivity to varenicline, effects on cessation, replication, and generalizability to African ancestry (AA) individuals. The top GWAS variant associated with abnormal dreams was rs901886, mapping to intron 2 of ICAM5 on chromosome 19. The prevalence of abnormal dreams in those with rs901886 CC, CT, and TT genotypes was 15%, 36%, and 62%, respectively (odds ratio = 2.94 for T vs. C, 95% confidence interval = 1.92-4.55, P = 2.03e-7; T allele frequency = 52%). This rs901886 association was selective to varenicline (P values > 0.05 on nicotine patch and placebo). There were also positive associations for rs901886 T (vs. C allele, P = 0.03) and for abnormal dreams (P = 0.06) with varenicline-aided cessation. Neither rs901886 (P = 0.40) nor abnormal dreams (P = 0.24) were associated with adherence. A similar direction of effect of rs901886 on abnormal dreams was observed in a second varenicline trial (NCT01836276). In AA individuals (n = 137), rs901886 was not associated with abnormal dreams (P = 0.41), but there was an association for a variant located ~ 74.4 kb 5' of ICAM5 (P = 2.56e-3). Variation in ICAM5 may influence abnormal dreams and cessation on varenicline. These findings provide additional support for genetically optimized smoking cessation approaches.

A scoping review of smoking cessation pharmacogenetic studies to advance future research across racial, ethnic, and ancestral populations

Abstinence rates among smokers attempting to quit remain low despite the wide availability and accessibility of pharmacological smoking cessation treatments. In addition, the prevalence of cessation attempts and abstinence differs by individual-level social factors such as race and ethnicity. Clinical treatment of nicotine dependence also continues to be challenged by individual-level variability in effectiveness to promote abstinence. The use of tailored smoking cessation strategies that incorporate information on individual-level social and genetic factors hold promise, although additional pharmacogenomic knowledge is still needed. In particular, genetic variants associated with pharmacological responses to smoking cessation treatment have generally been conducted in populations with participants that self-identify as White race or who are determined to be of European genetic ancestry. These results may not adequately capture the variability across all smokers as a result of understudied differences in allele frequencies across genetic ancestry populations. This suggests that much of the current pharmacogenetic study results for smoking cessation may not apply to all populations. Therefore, clinical application of pharmacogenetic results may exacerbate health inequities by racial and ethnic groups. This scoping review examines the extent to which racial, ethnic, and ancestral groups that experience differences in smoking rates and smoking cessation are represented in the existing body of published pharmacogenetic studies of smoking cessation. We will summarize results by race, ethnicity, and ancestry across pharmacological treatments and study designs. We will also explore current opportunities and challenges in conducting pharmacogenomic research on smoking cessation that encourages greater participant diversity, including practical barriers to clinical utilization of pharmacological smoking cessation treatment and clinical implementation of pharmacogenetic knowledge.

Accuracy and applications of sequencing and genotyping approaches for CYP2A6 and homologous genes

OBJECTIVES

We evaluated multiple genotyping/sequencing approaches in a homologous region of chromosome 19, and investigated associations of two common 3'-UTR CYP2A6 variants with activity in vivo.

METHODS

Individuals (n = 1704) of European and African ancestry were phenotyped for the nicotine metabolite ratio (NMR), an index of CYP2A6 activity, and genotyped/sequenced using deep amplicon exon sequencing, SNP array, genotype imputation and targeted capture sequencing. Amplicon exon sequencing was the gold standard to which other methods were compared within-individual for CYP2A6, CYP2A7, CYP2A13, and CYP2B6 exons to identify highly discordant positions. Linear regression models evaluated the association of CYP2A6*1B and rs8192733 genotypes (coded additively) with logNMR.

RESULTS

All approaches were ≤2.6% discordant with the gold standard; discordant calls were concentrated at few positions. Fifteen positions were discordant in >10% of individuals, with 12 appearing in regions of high identity between homologous genes (e.g. CYP2A6 and CYP2A7). For six, allele frequencies in our study and online databases were discrepant, suggesting errors in online sources. In the European-ancestry group (n = 935), CYP2A6*1B and rs8192733 were associated with logNMR (P < 0.001). A combined model found main effects of both variants on increasing logNMR. Similar trends were found in those of African ancestry (n = 506).

CONCLUSION

Multiple genotyping/sequencing approaches used in this chromosome 19 region contain genotyping/sequencing errors, as do online databases. Gene-specific primers and SNP array probes must consider gene homology; short-read sequencing of related genes in a single reaction should be avoided. Using improved sequencing approaches, we characterized two gain-of-function 3'-UTR variants, including the relatively understudied rs8192733.