Blood samples for both studies were collected and processed after informed consent using methods described in detail in previous publications (36, 37). DNA was genotyped at the Laboratory of Molecular Carcinogenesis Laboratory at the Georgetown University Lombardi Comprehensive Cancer Center (DRD2 rs1800497 & SLC6A3 VNTR – Studies 1 and 2) (Washington, D.C.), the University of Pennsylvania (COMT rs4680 – Study 2), the Primary Care Genetics Laboratory & Translational Research Center (DRD2 rs1800497 from additional Study 1 participants) (Pawtucket, RI), and the National Institute on Drug Abuse Molecular Neurobiology Laboratory (DRD4 VNTR & COMT rs4680 – Study 1) (Baltimore, MD), and the SRI International Center for Health Sciences Molecular Genetics Laboratory (DRD4 VNTR – Study 2) (Menlo Park, CA) using methods previously described (44–50).
