Limitations of our study include reliance on SNP genotyping and gene expression microarrays for the cis-eQTL mapping means that structural or rare genetic variants were not captured, coverage of common genetic variants was more complete for the participants of European ancestry compared to the African Americans, and only a single OPRM1 probe was represented. Future studies capturing more complete genetic variation and more localized expression patterns and measuring other brain regions relevant to addiction (66) may lead to the identification of other important regulatory polymorphisms associated with heroin addiction.
