MLLT3 and leukemia: There are at least three explanations for no apparent effect of PFGs on ROS, apoptosis, and DNA damage: (i) PFGs alone are not able to increase ROS, apoptosis, or DSBs in UCB cell populations; (ii) while PFGs may induce ROS, apoptosis, and DSBs, the number of PFG+ cells in positive probands is too low (RUNX1-RUNX1T1 (7/105) and KMT2A-MLLT3 (4.4/105)) for the detection of this induction; and, (iii) a secondary mutation leading to overt leukemia has to occur for genetic instability or disrupted DNA repair, which is observed in patients that suffer from leukemia with PFGs [56].