Juvenile myelomonocytic leukemia (JMML) is a rare pediatric MDS/MPN overlap syndrome that is characterized by somatic mutations in NF1, CBL, NRAS, KRAS or PTPN11 that result in the activation of RAS/MAPK or JAK/STAT signaling. This evidence concerns the gene NRAS and juvenile myelomonocytic leukemia.