In addition, over-expression of DNMT3b, but not DNMT1 and DNMT3a, is common in various cancer cells (Girault et al. 2003; Robertson et al. 1999; Saito et al. 2002), suggesting that DNMT3b plays an important role in the development of aberrant promoter methylation during oncogenesis. The gene discussed is DNMT1; the disease is cancer.