Despite initial encouraging data, there are several limitations of the smoking cessation genetic studies conducted to date. Many of the clinical trials have relatively small sample sizes (300–500 subjects). A large portion of the smoking population, such as ethnic minorities, are not accounted for in these studies. Larger sample sizes and studies that target various ethnic groups may help to identify novel genetic associations with smoking cessation. Another limitation is that the function of many of the gene variants examined is still unknown. At least for the genotype markers, eVect sizes tend to be small and the studies are not powered to detect gene–gene and gene–environment interactions important in cessation.
