Tobacco use is a major health problem in the United States and worldwide. Despite the increasing awareness of health related consequences, about 25% of American adults continue to smoke (Center for Disease Control 2000). Some individuals continue despite knowledge of the risks, and others do not understand the risks, but the majority of individuals continue smoking because they are nicotine dependent (Hymowitz et al, 1997; Jarvis, 2004). That is, despite having the desire to quit, a large percentage of smokers are unsuccessful in stopping. Studies have shown that genes influence level of nicotine dependence with heritability estimates indicating genetic factors account for between 40–70% of the phenotypic variance (Li et al, 2003; Maes et al, 2004; Rhee et al, 2003; Swan et al, 1990). Determining which genes are contributing to this heritability is an area of active research.
