that each study comprehensively assessed nicotine, alcohol, marijuana, and cocaine dependence. Whether or not the variation in this correlated cluster is specific to nicotine dependence is a key factor for improved understanding of the underlying biology of dependence. Finally, to examine the question of additional genetic associations to nicotine in this region, we performed analyses of rs4952 conditioned on the rs13273442 genotype. We targeted rs4952 as a potential second contributor to nicotine dependence in this region because it has been previously reported as associated to nicotine dependence (6), and it is only modestly correlated to rs13273442 (r2=0.103, D’=1.0 in European Americans, r2=0.005, D’=1.0 in African Americans). Knowledge of multiple signals in this region will help determine the focus of future genetic research.
