ID4 and acute myeloid leukemia: To investigate the consequence of promoter methylation, the expression of 3 of the genes with the most consistent methylated promoters in AML was performed i.e. DPP6 (absolute methylation difference = 0.46, P = 0.0007), SPHKAP (absolute methylation difference = 0.45, P = 0.0002) and ID4 (absolute methylation difference = 0.28, P = 0.003).