GGH and acute lymphoblastic leukemia: Cheng et al [8] reported that methylation of CpG island 1 (CpG1) in the promoter region of GGH was acute lymphoblastic leukemia-cell specific and had a significant effect on GGH expression, whereas methylation of CpG2 was common in both ALL cells and normal leukocytes but did not significantly change GGH expression.