The OPRM1 gene is located at cytogenetic band 6q25.2. The major subtype contains 4 exons. A number of alternatively-spliced variants have been reported in rodents and humans. Two human receptor variants (encoded by splice variants) (hMOR-1X and hMOR-1O) were identified (Pan 2003). An alternatively-spliced exon with a specific promoter was identified -28 kb upstream of exon 1 (Xu et al. 2009). An alternatively-spliced exon with an alternative promoter was identified in rodents and humans (Shabalina et al. 2009). Notably, the genomic organization of the human OPRM1 locus is highly similar to the mouse locus. However, alternative-splicing events display some substantial differences between human and mouse.
