Promoter regions in AML blasts exhibit decreased levels of H3Ac. (A) The top 300 gene-associated genomic regions differing in H3 acetylation patterns between AML (n = 72) and CD34⁺ progenitors (n = 17) were hierarchically clustered. Green color indicates higher H3Ac levels, whereas red color indicates lower H3Ac levels. AML samples are indicated by the red bar on top of the heat map, and CD34⁺ progenitors are indicated in green. H3 acetylation of the PRDX2 promoter region is indicated. A full list of differentially acetylated genomic regions is shown in supplemental Table 1. (B) PCA was applied to the top 100 probes with different intensity values between AML, CD34, and white blood cells. Because of the overlap, overall 259 probes were used in the PCA analysis. (C) This histogram depicts the numbers of differentially acetylated regions with respect to their distance from the TSSs. No differences in the frequency of increased versus decreased acetylation levels were observed at distances > 300 bases upstream of the TSS. In contrast, in the core promoter region, losses of H3 acetylation were much more frequent in AML than increases. (D) The PRDX2 promoter was strongly hypoacetylated in AML specimens (n = 71) compared with normal CD34⁺ cells (n = 17). The probes located at −38 (P = .006) and +396 (P = .014) with regard to the TSS showed significantly lower H3 acetylation even after adjustment for multiple testing of all array probes.