While discrepancies with respect to the incidence of genomic IKZF1 deletions as well as their independent prognostic impact have been noted [3-7], it has generally been assumed that IKZF1 is a haploinsufficient gene rendering its hemizygous deletions in ALL cells biologically and clinically significant by causing IK deficiency at the cellular level [2-7]. The gene discussed is IK; the disease is acute lymphoblastic leukemia.