Reduced PRDX4 expression in APL is associated with a bivalent histone methylation mark, i.e., the combination of repressive histone methylation mark H3K27me3 and the activating histone methylation mark H3K4me3, at the TSS of PRDX4 but not with DNA methylation of CpG islands in its promoter region. The gene discussed is PRDX4; the disease is acute promyelocytic leukemia.