For phenotype definition, of course, it would be great if we had biomarker information on those samples, which is impossible for the time being, given the assay cost associated with biomarkers and the unavailability of materials for many of those samples in the Korean population. As far as we know, however, smoking behaviors in almost all reported studies were based on questionnaires, with the number of cigarettes smoked per day being the most commonly used (Li 2008), and only limited studies used the biomarkers. Thus, further GWAS study on ND in an Asian sample with better assessment of smoking behavior, including biomarker information, is warranted.
