RUNX1 is known to play critical roles in hematopoiesis (Mangan and Speck, 2011), and is commonly mutated in leukemia as a tumor suppressor (Blyth et al., 2005; Mangan and Speck, 2011; Zhang et al., 2012), including in MLL-ENL driven leukemias (Nishimoto et al., 2011). Here, MLLT1 is linked to leukemia.