Therefore, NF1 deficiencies act as functional equivalents of activating mutations in RAS.62 Inactivating NF1 mutations lead to the development of a human developmental disorder, the Neurofibromatosis 1, characterized by mental retardation, facial dysmorphism, and increased risk for developing malignant tumors, including JMML and AML.63,64 Few studies have also reported NF1 deletions in KMT2A-rearranged leukemias (Fig. 2 and Supplemental Table 1, Supplemental Digital Content).31,37. Here, NF1 is linked to neurofibromatosis type 1.