RUNX1 and acute myeloid leukemia: PHF6 mutations co-occur in MDS/AML with mutations in RUNX1, ASXL1, and U2AF1 [11, 13, 16], with the majority of PHF6 mutations being frameshift and nonsense mutations distributed throughout the gene body [16], predicted to produce null alleles and indicating that PHF6 acts as a leukemia suppressor.