AFF1 and leukemia: It is also important to note that AFF1, AF9, and ENL are among the most frequent oncogenic fusion partners with the MLL gene product that transforms early hematopoietic progenitors and causes childhood leukemia by short-circuiting enhancer and promoter activation and transcriptional elongation checkpoint controls (Krivtsov and Armstrong, 2007, Shilatifard, 2012, Slany, 2009, Smith et al., 2011).