This has been the subject of recent reviews [52,53], but in brief, the ETV6-RUNX1 and TCF3-PBX1 fusions have been detected in DBSs in up to 5% and 0.6% of healthy newborns, respectively, frequencies much higher than the incidences of these leukemia subtypes, thus supporting that additional mutations are required for progression to overt leukemia. This evidence concerns the gene TCF3 and leukemia.