RUNX1 and myelodysplastic syndrome: To date, the RUNX1 gene (previously AML1, CBFA2 in 21q22) has been shown to fuse in-frame with 23 different partner genes, encoding a structurally heterogeneous group of proteins, in acute myeloid and lymphoblastic leukemia (AML and ALL), chronic myeloid leukemia (CML; the fusion here occurs secondarily), and myelodysplastic syndromes (MDS) (2,3).