While TDG is known for its causing significant embryonic lethality phenotype when mutated, and its defined role in active demethylation,15, 16Mbd4 mutant mice develop normally and do not show a dramatic increase in cancer susceptibility25, 26, 27; however, an increased number of C to T transition mutations at CpG sites are noted, that is, CpG to CpA or CpG to TpG, as expected due to unrepaired G:T mismatches.25, 26. The gene discussed is TDG; the disease is cancer.