Many twin studies in the US and other countries hav consistently implied that genetic factors contribute to th risk of becoming a regular smoker. Initial evidence for genetic influences on nicotine dependence (ND) cam from cross-sectional studies of twins that showed a mean heritability of 0.53 (range 0.28–0.84) for cigarette smoking (for reviews, see Carmelli et al. 1992; Hughes 1986). Our meta-analysis of the genetic parameter estimates for smoking initiation (SI) and ND based on 17 twin studies determined that the weighted mean heritability is 0.50 and 0.59, respectively, for all smokers (Li et al. 2003). Complex segregation analyses of smoking behavior in 49 three-generation families supported a dominant major gene effect with residual familial correlation (Cheng et al 2000).
