A recent study suggested that a second nearby variant within OPRM1, rs3778150, is robustly associated with heroin dependence and fully explained a smaller observed association with rs1799971.
The present pilot study characterized the impact of OPRM1 genotype (rs1799971, 118G allele carriers vs. 118AA homozygotes) on heroin-use phenotypes associated with heroin dependence severity in a sample of male, Caucasian chronic heroin users (n = 86).
On the other hand, significant association was observed for A118G with heroin addiction (χ²=7.268, P=0.0264) as well as with alcoholic addition (χ²=6.626, P=0.0364).
For the A118G polymorphism, we found significant differences in allele and genotype frequencies between different ethnic groups and highly significant association with heroin dependence in Indians for both genotype distribution (p = 0.024) and allele frequency (p = 0.009).