Ethnic specificity was also found at specific CpG sites that were significantly different between former heroin addicts and controls. In African-Americans, the +12 CpG site was hypomethylated in the former heroin addicts. The +12 CpG site was not found to differ significantly, point-wise or experiment-wise, by age, sex, or history of alcoholism in the African-American cases or controls. In Hispanics, a different set of CpG sites had methylation levels that differed between cases and controls. Three sites (−25, −14, and +27) were hypermethylated in the Hispanic former heroin addicts compared to controls. None of these three CpG sites were found to have methylation levels that differed significantly, point-wise or experiment-wise, with age, sex, or history of alcoholism in the Hispanic cases or controls. Overall, three (−25, −14, and +12) of five (−80, −25, −14, −10, and +12) CpG sites with point-wise significant differences in methylation levels in the controls among the ethnicities had experiment-wise significant differences between cases and controls in either the African-Americans or Hispanics.
