MedGen

Noonan syndrome-like disorder with or without juvenile myelomonocytic leukemia (NSLL) is a developmental disorder resembling Noonan syndrome (NS1; 163950) and is characterized by facial dysmorphism, a wide spectrum of cardiac disease, reduced growth, variable cognitive deficits, and ectodermal and musculoskeletal anomalies. There is extensive phenotypic heterogeneity and variable expressivity. Patients with heterozygous germline CBL mutations have an increased risk for certain malignancies, particularly juvenile myelomonocytic leukemia (JMML; 607785), as seen in patients with Noonan syndrome (summary by Martinelli et al., 2010 and Niemeyer et al., 2010). [from OMIM]

Juvenile myelomonocytic leukemia is an aggressive pediatric myelodysplastic syndrome (MDS)/myeloproliferative disorder (MPD) characterized by malignant transformation in the hematopoietic stem cell compartment with proliferation of differentiated progeny (Loh et al., 2009). JMML constitutes approximately 30% of childhood cases of myelodysplastic syndrome and 2% of leukemia (Hasle et al., 1999). Although JMML is a progressive and often rapidly fatal disease without hematopoietic stem cell transplantation (HSCT), some patients have been shown to have a prolonged and stable clinical course without HSCT (Niemeyer et al., 1997). Chronic myelomonocytic leukemia (CMML) is a similar disorder with later onset. Both JMML and CMML have a high frequency of mutations affecting the RAS signaling pathway and show hypersensitivity to stimulation with GM-CSF, which causes STAT5 (601511) hyperphosphorylation (Loh et al., 2009). Genetic Heterogeneity of Juvenile Myelomonocytic Leukemia In up to 60% of cases of JMML, the RAS/MAPK pathway is deregulated due to somatic mutations in the PTPN11 (176876), KRAS (190070), and NRAS (164790) genes. Additionally, both germline and somatic mutations in the CBL gene have been found in patients with JMML, indicating a frequency of 10 to 15% of JMML patients overall (Loh et al., 2009). Somatic disruptions of the GRAF gene (ARHGAP26; 605370) have also been found in patients with JMML. About 10 to 15% of JMML cases arise in children with neurofibromatosis type I (NF1; 162200) due to germline mutations in the NF1 gene (613113). In addition, patients with Noonan syndrome (NS1, 163950; NS3, 609942) or Noonan syndrome-like disorder (NSLL; 613563) due to germline mutations in the PTPN11, KRAS2, and CBL genes, respectively, also have an increased risk of developing JMML. Genetic Heterogeneity of Chronic Myelomonocytic Leukemia Somatic mutations in the CBL, ASXL1 (612990), TET2 (612839), and SF3B1 (605590) genes have been found in patients with CMML. [from OMIM]