for linkage of smoking behavior to chromosome 5q has been reported from an analysis of the COGA data [5]. The linkage to smoking behavior on chromosome 5 was also reported by another study with a different linkage analysis method but at a marginal level of significance [6]. In another independent study, Straub et al. [4] identified several possible regions for nicotine dependence on chromosomes 2, 4, 10, 16, 17 and 18 in the Christchurch sample of New Zealand but failed to confirm these regions in the Richmond sample of Virginia. This was probably due to insufficient statistical power as a result of the small sample size of the Richmond cohort (91 families with 264 genotyped individuals). Compared with the research described above, a much larger sample size was used in the present study, which may contribute partially to the significant p-values obtained in this study.
