Tobacco use is one of the leading causes of mortality worldwide. Because most regular smoking occurs in the context of nicotine dependence, nicotine dependence is frequently the focus of studies on tobacco use(1). Among current smokers, approximately 60% are nicotine dependent based on the Fagerström Test for Cigarette Dependence (FTCD), a well-established scale for assessing nicotine dependence(2). Evidence for genetic factors contributing to the risk of smoking behaviors and nicotine dependence is seen in the clustering of heavy smoking and nicotine dependence in families and the similarity of smoking behaviors in genetically identical twins(3–4).
