"Intention to Analyze" in Pharmacogenomics Studies

Pharmacogenetics of smoking cessation in general practice: results from the patch II and patch in practice trials

INTRODUCTION

Cigarette smoking remains the leading cause of preventable death worldwide. However, the efficacy of available first-line therapies remains low, particularly in primary care practice where most smokers seek and receive treatment. These observations reinforce the notion that 'one size fits all' smoking cessation therapies may not be optimal. Therefore, a translational research effort was launched by the Imperial Cancer Research Fund (later Cancer Research UK) General Practice Research Group, who led a decade-long research enterprise that examined the influence of pharmacological hypothesis-driven research into genetic influences on drug response for smoking cessation with transdermal nicotine replacement therapy in general practice.

METHODS

New and previously published smoking cessation genetic association results of 30 candidate gene polymorphisms genotyped for participants in two transdermal nicotine replacement clinical trials based in UK general practices, which employed an intention to analyze approach.

RESULTS

By this high bar, one of the polymorphisms (COMT rs4680) was robust to correction for multiple comparisons. Moreover, future research directions are outlined; and lessons learned as well as best-practice models for designing, analyzing, and translating results into clinical practice are proposed.

CONCLUSIONS

The results and lessons learned from this general practice-based pharmacogenetic research programme provide transportable insights at the transition to the second generation of pharmacogenetic and genomic investigations of smoking cessation and its translation to primary care.

Lack of association of DRD2 rs1800497 (Taq1A) polymorphism with smoking cessation in a nicotine replacement therapy randomized trial

INTRODUCTION

We previously reported evidence that the T allele of the dopamine type-2 receptor (DRD2) rs1800497 polymorphism is associated with improved response to nicotine replacement therapy (NRT) relative to placebo and that this association may only be present in females. However, evidence of the poor replication validity of genetic association studies is growing, particularly among those that report subgroup analyses. We therefore attempted to replicate our previous finding of an association between the DRD2 rs1800497 genotype and response to NRT in a new, larger cohort, with greater statistical power.

METHODS

Participants were randomly assigned to one of two levels of smoking cessation behavioral support (usual care vs. weekly support). All participants received 8 weeks of 15-mg NRT transdermal patch.

RESULTS

The presence of one or more T alleles was associated with a slightly but not significantly lower likelihood of abstinence at 3 and 6 months. We found evidence of a genotype x sex interaction effect. However, stratified analyses indicated a main effect of genotype opposite to the effect reported previously, with females carrying one or more copies of the T allele less likely to be abstinent.

DISCUSSION

Our results do not support an association between the DRD2 rs1800497 (Taq1A) polymorphism and response to NRT, contrary to our previous study.