One hundred sixty-seven case and 106 control samples, with a correlation of ≥ 0.7 between the forward and reverse analyses, were analyzed further (Table 1). Methadone-stabilized former heroin addicts were found to have significantly higher methylation than controls at two CpG sites (Figure 3). At the −18 CpG site, the level of methylation was 25.4% in cases and 21.4% in controls [p = 0.0035, GEE; p = 0.0077, t-test]. At the +84 CpG site the level of methylation was 7.43% in cases and 5.62% in controls (p = 0.0095, GEE; p = 0.0067, t-test). The difference in methylation at the −18 CpG site was significant experiment-wise when evaluated by FDR (0.048), but was only point-wise significant for the +84 CpG site (0.080) (Benjamini et al, 1995).
