Methylation-specific PCR shows ABL1 methylation patterns in CML cell lines. NBC, normal donor buffy-coat DNA; SssI-NBC, normal donor buffy-coat DNA treated in vitro with CpG methylase (SssI methylase); EM2, DNA from CML cell line EM2 containing only a duplicate of the Ph′ chromosome and lacking a normal homologue of chromosome 9; K562, DNA from cell line K562 which contains 3 copies of the Ph′ chromosome in addition to a chromosome 9 homologue; M, primers specific for methylated DNA; U, primers specific for unmethylated DNA; ◊x, ◊x/HaeIII marker.