RUNX1: The RUNX1 gene provides instructions for making a protein called runt-related transcription factor 1 (RUNX1). Like other transcription factors, the RUNX1 protein attaches (binds) to specific regions of DNA and helps control the activity of particular genes. This protein interacts with another protein called core binding factor beta or CBFβ (produced from the CBFB gene), which helps RUNX1 bind to DNA and prevents it from being broken down. Together, these proteins form one version of a complex known as core binding factor (CBF). The RUNX1 protein turns on (activates) genes that help control the development of blood cells (hematopoiesis). In particular, it plays an important role in development of hematopoietic stem cells, early blood cells that have the potential to develop into all types of mature blood cells such as white blood cells, red blood cells, and platelets. A rearrangement (translocation) of genetic material involving the RUNX1 gene is found in approximately 7 percent of individuals with a form of blood cancer known as acute myeloid leukemia (AML). The translocation, written as t(8;21), combines genetic information from chromosome 21 and chromosome 8, fusing the RUNX1 gene on chromosome 21 with a gene on chromosome 8 called RUNX1T1 (also known as ETO). Because this genetic change affects CBF, the condition is classified as core binding factor AML (CBF-AML). The resulting fusion protein, RUNX1-ETO, is able to form CBF and attach to DNA, like the normal RUNX1 protein; however, instead of turning genes on, it turns them off. This change in gene activity blocks the maturation (differentiation) of blood cells and leads to the production of abnormal, immature white blood cells called myeloid blasts. While t(8;21) is important for leukemia development, a mutation in one or more additional genes is typically needed for the myeloid blasts to develop into cancerous leukemia cells.