When we compared ethnic differences in DNA methylation in the controls, the average methylation level of all 16 CpG sites was significantly higher in the African-Americans than in the Hispanics or the Caucasians. There was no difference in overall methylation level between the Hispanic and the Caucasian controls. However, when we compared ethnic differences in DNA methylation at individual CpG sites, methylation levels at the majority of the CpG sites (14 of 16) were not different. Methylation at the −25 and the +12 CpG sites showed the biggest difference among ethnicities. The −25 CpG site was methylated less in the Hispanics when compared with the African-Americans and the Caucasians, both of which had similar methylation levels. The +12 CpG site had the lowest level of methylation in the Hispanics, an intermediate level of methylation in the Caucasians, and the highest level in the African-Americans. At this time, the mechanisms regulating methylation at specific CpG sites are not known.
