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 association with CNIH3 (3). Additionally, we used GWAS to identify a variant close to the OPRM1 locus that affected opioid dose requirements in AAs (4). These studies demonstrated that the use of an ordinal trait can provide more statistical power than a categorical diagnosis, as it can take account of affection severity.
