Our results of ethnic differences in DNA methylation were not unexpected. Ethnic diversity in overall DNA methylation has been observed in leukocyte DNA (Terry et al. 2008) and in studies on the development of cancers (e.g. Tomii et al. 2006). In contrast to our finding in a specific genomic region, the Terry et al. (2008) study found whole genome methylation of leukocyte DNA was highest in Hispanics, intermediate in Whites, and lowest in Blacks. Ethnic differences in the frequency and distribution of genetic polymorphisms also are well documented (Lao et al. 2006). The frequency of variants in genes whose products are involved in the methylation of DNA differs among ethnicities, such as in the genes coding for DNA methyltransferase 2 (Franchina and Kay 2001) and 3B (Zhao et al. 2009). Some of these variants may alter the expression and function of the enzymes involved in DNA methylation and demethylation.
