Three major haplogroups were identified in our previous study of European Americans (350 cases and 184 controls) based on OPRM1 exon 1 SNP rs1799971 (118A>G, #5), and intron 1 SNPs rs510769 (#6) and rs3778151 (#8).9 The major haplogroups identified are: 1) “REF” (65%, 56%); 2) “118G” (13%, 11%); and 3) “INT1” (13%, 20%) in controls and cases, respectively. The higher frequency of the “REF” group may be explained by the fact that the haplogroup of “block 2” cannot be distinguished from the reference group by the three SNPs genotyped. These results demonstrate the higher frequency of the “INT1” haplogroup in the cases that was the basis for the association of this haplogroup with heroin addiction. The allele frequencies in controls are compatible with the HapMap data from Caucasians.
