Even when clinical and hematological criteria must be evaluated for establishing a diagnosis of JMML, it has been described that around 90% of patients harbor molecular alterations in one of five RAS pathway genes (PTPN11, NRAS, KRAS, NF1 or CBL), which define genetically and clinically distinct subtypes (Table 3 and Figure 5). Here, NF1 is linked to juvenile myelomonocytic leukemia.