The C/EBPδ promoter is hypermethylated in acute myeloid leukemia. (A) The number of hypermethylated CpGs in the promoter region of the C/EBP family members was analyzed in AML patients and controls by MALDI-TOF. Hypermethylation was defined as methylation above the mean methylation levels in controls plus 2 times the controls' standard deviation. The number of hypermethylated CpGs was analyzed for each sample and each gene. (B) The C/EBPδ promoter was methylated at a high frequency in AML. The bars indicate the percent of AML patients' samples hypermethylated for the different C/EBP genes as assessed by MALDI-TOF. (C-D) Correlation between C/EBPδ promoter methylation and mRNA expression. C/EBPδ promoter methylation was associated with decreased C/EBPδ expression levels (P = .005). The scatter plot indicates the relative mRNA expression levels normalized to GAPDH with regard to a low (up to 5 hypermethylated CpGs), intermediate (6 to 15 hypermethylated CpGs), and high (more than 150 methylated CpGs) degree of C/EBPδ promoter methylation (P = .016, nonparametric test). The median level of expression is indicated for each group with a horizontal line.