KMT2A and leukemia: Compared with non-MLL leukemia, children with MLL-r positive ALL have clinical features that are different from other types of leukemia, mainly high white blood cell count (WBC) at disease onset, insensitivity to traditional chemotherapeutic agents, low complete remission rate (CR), and short survival and poor outcome [4–6], which is why the South China Children’s Leukemia Group [7] classified children with MLL-r positive ALL as a high-risk group.