In the present study, we used an ordinal trait analysis that was limited to OD-exposed individuals in our GWAS. We identified a variant of RGMA, which encodes the RGM domain family member A (RGMa, which was associated with OD in EAs at a genome-wide significant (GWS) level. The opioid-exposed EA subjects we studied previously (2) are included in the present study, augmented by additional subjects recruited more recently and we used a new analytic strategy that included only OD-exposed subjects. The finding was then replicated in both EAs and AAs.
