Whole genome sequencing of a wide range of ethnic groups has identified 3324 polymorphisms in the OPRM1 gene, which occupies a 200kb region on the long arm of chromosome 6 (http://www.1000genomes.org). Many of these polymorphisms occur at extremely low frequencies and have limited relevance at the population level. However, 1395 of the genetic variants have minor allele frequencies greater than 1% in the global population. These more common variants are more likely to be relevant in large scale genetic studies. There are 2 common nonsynonomous SNPs and an additional 3 synonymous coding variants. The small number of coding polymorphisms suggests selective pressure against genetic variation in the exonic regions of OPRM1.
