This study demonstrates ethnic diversity of DNA methylation globally and at specific CpG sites. Several of the CpG sites that we analyzed were significantly different experiment-wise among the ethnicities. This finding has implications for future studies on the role of DNA methylation. Population stratification has been found to produce false-positive and false-negative findings in genetic studies (Enoch et al. 2006). Possible confounding factors, such as population structure, must be addressed in future DNA methylation studies. We have demonstrated significant differences in DNA methylation between former heroin addicts and controls specific to each ethnicity. This extends our previous study on Caucasians and demonstrates that DNA methylation may play a role in heroin addiction or pharmacotherapy in African-Americans and Hispanics.
