Activating mutations in either NRAS or KRAS genes occur in AML, juvenile myelomonocytic leukaemia (JMML), chronic myelomonocytic leukaemia (CMML) [124], childhood ALL [125] and myelodysplastic syndromes (MDS) [126]. The gene discussed is KRAS; the disease is chronic myelomonocytic leukemia.