The goal of this study is to explore these three questions. To examine consistency of the genetic association across populations, we meta-analyzed three independent studies of substance dependence, which collectively include 5171 subjects of European American and African American descent. Comparing results in both populations is essential for determining whether a finding can be generalized and may help identify contributors to health disparities between African Americans and European Americans (9). For example, although African Americans smoke fewer cigarettes than European Americans, they have a higher incidence of lung cancer (76 vs. 70 per 100,000) (10). This health disparity underscores the need for studies to identify genetic factors contributing to nicotine dependence in African Americans. To test whether the genetic association is specific to nicotine dependence or whether rs13273442 tags a non-specific genetic liability to substance dependence, we utilized the fact 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
