c-CBL (CBL) encodes a member of the Cbl family of proteins, which functions as an E3 ubiquitin ligase. We describe a dominant developmental disorder resulting from germline missense CBL mutations, which is characterized by constitutional anomalies that include impaired growth, developmental delay, cryptorchidism, and a predisposition to juvenile myelomonocytic leukemia (JMML). Some individuals experienced spontaneous regression of their JMML but developed vasculitis later in life. Importantly, JMML specimens from affected children show loss of the normal CBL allele through acquired isodisomy. Consistent with these genetic data, the common p.Y371H mutant Cbl protein induces cytokine-independent growth and constitutive phosphorylation of ERK, AKT, and S6 only in hematopoietic cells in which normal Cbl expression is reduced by RNA interference. We conclude that germline CBL mutations have developmental, tumorigenic, and functional consequences that are reminiscent of disorders that are caused by hyperactive Ras/Raf/MEK/ERK signaling and include neurofibromatosis type 1, and Noonan, Costello, cardiofaciocutaneous, and Legius syndromes.

Juvenile myelomonocytic leukemia is an aggressive myeloproliferative disorder characterized by malignant transformation in the hematopoietic stem cell compartment with proliferation of differentiated progeny. Seventy-five percent of patients harbor mutations in the NF1, NRAS, KRAS, or PTPN11 genes, which encode components of Ras signaling networks. Using single nucleotide polymorphism arrays, we identified a region of 11q isodisomy that contains the CBL gene in several JMML samples, and subsequently identified CBL mutations in 27 of 159 JMML samples. Thirteen of these mutations alter codon Y371. In this report, we also demonstrate that CBL and RAS/PTPN11 mutations were mutually exclusive in these patients. Moreover, the exclusivity of CBL mutations with respect to other Ras pathway-associated mutations indicates that CBL may have a role in deregulating this key pathway in

Summary Progress in understanding the molecular pathogenesis of human myeloproliferative disorders (MPDs) has led to guidelines incorporating genetic assays with histopathology during diagnosis. Advances in flow cytometry have made it possible to simultaneously measure cell type and signaling abnormalities arising as a consequence of genetic pathologies. Using flow cytometry, we observed a specific evoked STAT5 signaling signature in a subset of samples from patients suspected of having juvenile myelomonocytic leukemia (JMML), an aggressive MPD with a challenging clinical presentation during active disease. This signature was a specific feature involving JAK-STAT signaling, suggesting a critical role of this pathway in the biological mechanism of this disorder and indicating potential targets for future therapies. Significance Recent advances have enabled simultaneous measurement of cell type and cell signals in primary populations using flow cytometry. This technique enables the question, "Can we track oncogenic cell populations from diagnosis through disease evolution via signaling?" Doing so in an era of using specific inhibitors against components of key signal transduction pathways will be necessary to assess treatment effects in human patients and adapt as cancer cells alter their signaling in response to these treatments. This work uses such an approach to follow patients over time and shows that disease status in juvenile myelomonocytic leukemia (JMML) -- at diagnosis, remission, relapse, and transformation -- is indicated by a subset of cells with an abnormal signaling profile.