Differences in methylation were determined between methadone stabilized former severe heroin addicts and controls within each ethnicity. In 170 African-Americans, significant point-wise differences in methylation levels were found between the former heroin addicts and the controls at the −93 (P = 0.0361), −90 (P = 0.0406), and +12 (P = 0.0002) CpG sites (Table 5a, b). At two of these three CpG sites, cases were hypermethylated compared with controls. When corrected for multiple testing, the only difference in methylation levels between cases and controls was at the +12 CpG site (experiment-wise P = 0.0032). The +12 CpG site was hypomethylated in the former heroin addicts (6.6%) compared to that found in the controls (12.2%).
