Opioid dependence (OD) is a major cause of medical, legal, and social problems, resulting in increased mortality and decreased productivity. It is presently at epidemic levels in the United States. OD is a genetically complex disorder that is influenced by complex environmental factors (1), such as drug availability, making it difficult to identify genetic factors that underlie the disorder. Genome-wide association study (GWAS) is an unbiased way to search for novel genetic factors contributing to OD. We completed the first GWAS of OD (with DSM-IV criterion count as the phenotype definition, using all available subjects) and found two genome-wide significant single nucleotide polymorphisms (SNPs) in African-Americans (AAs) (2). These two SNPs map to KCNC1 (potassium voltage-gated channel subfamily C member 1) and KCNG2 (potassium voltage-gated channel modifier subfamily G member 2), respectively, which are involved in potassium signaling pathways. Pathway-based GWAS analysis also demonstrated an enrichment of genes involved in calcium signaling and long-term potentiation (2). There have been fewer findings in European-Americans (EAs), where the only GWAS to date to identify variants associated to OD in EAs showed an
