To clarify the relationship between FTCD-based nicotine dependence and CPD in the context of a genome-wide association study, we defined FTCD-based nicotine dependent cases and non-nicotine dependent controls from the Study of Addiction: Genetics and Environment (SAGE), a multi-ethnic, case-control sample selected for alcohol dependence(22). By including a diverse set of study participants, we have the opportunity to extend our investigation beyond the previous studies in European-Americans, and specifically address the role that phenotype definition plays in genome-wide association studies.
