It is intriguing that the SNPs with the lowest P values for association with heroin addiction in the AA populations, in this study, and the EA population in our recent study (Levran et al., 2008), are so distinct. One possible explanation for these findings is the differences in allele frequencies between the two populations that are observed for 18 SNPs out of the total of 26 SNPs indicated in both studies and are supported by the HapMap data. The results for the rest of the SNPs, if their association with heroin addiction is validated, can not be explained by allele frequency differences and may be influenced by other factors such as LD pattern or modifier genes that may be different in these populations.
