PTPN11 and juvenile myelomonocytic leukemia: The common molecular denominator of JMML is the deregulation of the intracellular Ras signal transduction pathway, caused in >90% of cases by mutations in one (or, rarely, more than one) of five primordial genes (PTPN11, NRAS, KRAS, NF1, or CBL) [5].