MedGen

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]

A reactive lesion characterized by the presence of a bland histiocytic cellular infiltrate admixed with giant cells. [from NCI]

Neurofibromatosis 1 (NF1) is a multisystem disorder characterized by multiple café au lait macules, intertriginous freckling, multiple cutaneous neurofibromas, and learning disability or behavior problems. About half of people with NF1 have plexiform neurofibromas, but most are internal and not suspected clinically. Plexiform neurofibromas can cause pain, neurologic deficits, and abnormalities of involved or adjacent structures. Less common but potentially more serious manifestations include optic nerve and other central nervous system gliomas, malignant peripheral nerve sheath tumors, scoliosis, tibial dysplasia, vasculopathy, and gastrointestinal, endocrine, or pulmonary disease. [from GeneReviews]

Juvenile xanthogranuloma is the most common type of non-Langerhans cell histiocytosis (see this term) characterized by the occurrence of one or more reddish or yellowish self-limiting and benign papules or nodules of several millimeters in diameter, usually appearing on the head and neck (but sometimes on the extremities and trunk) during the first year of life (or rarely in adulthood) and usually regressing spontaneously. Extracutaneous involvement has also been reported, involving most commonly the eye (uveal tract) but with other locations including the central nervous system, lung, liver, bones and endocrine glands, and may be associated with considerable morbidity. [from ORDO]

A procedure to replace diseased bone marrow with transplanted healthy bone marrow cells. [from NCI]

Cafe-au-lait spots are hyperpigmented lesions that can vary in color from light brown to dark brown with smooth borders and having a size of 1.5 cm or more in adults and 0.5 cm or more in children. [from HPO]

A benign peripheral nerve sheath tumor that generally appears as a soft, skin-colored papule or small subcutaneous nodule. Individuals with neurofibromatosis can have numerous neurofibromas. [from HPO]

A rare benign tumor composed entirely of neoplastic perineurial cells. It may occur in the soft tissues, intraneurally or in mucosal sites. [from NCI]

A rare cutaneous lesion composed of eosinophilic histiocytes, which are often multinucleated. The lesions are yellow-brown papules affecting any part of the body. Patients are usually adult men. The prognosis is excellent. -- 2003 [from NCI]

A rare benign peripheral nerve sheath tumor characterized by a well-demarcated intraneural or diffusely infiltrative extraneural space-occupying lesion consisting of Schwann cells, perineurial-like cells, and fibroblasts. It presents as a cutaneous nodule, a circumscribed mass in a peripheral nerve, a plexiform enlargement of a major nerve trunk, or with diffuse but localized involvement of skin and subcutaneous tissue. Multiple neurofibromas are typically associated with neurofibromatosis 1. Malignant transformation occurs almost exclusively in plexiform neurofibromas and neurofibromas of major nerves. [from ORDO]

Group of disorders which feature accumulations of active HISTIOCYTES and LYMPHOCYTES, but where the histiocytes are not LANGERHANS CELLS. The group includes HEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS; SINUS HISTIOCYTOSIS; xanthogranuloma; reticulohistiocytoma; juvenile XANTHOGRANULOMA; xanthoma disseminatum; as well as the lipid storage diseases (SEA-BLUE HISTIOCYTE SYNDROME; and NIEMANN-PICK DISEASES). [from MONDO]

Noonan syndrome-like disorder is a developmental disorder resembling Noonan syndrome (NS1; 163950) and 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 (summary by Martinelli et al., 2010). Patients with heterozygous germline CBL mutations have an increased risk for certain malignancies, particularly juvenile myelomonocytic leukemia (JMML; 607785), as also seen in patients with Noonan syndrome (summary by Niemeyer et al., 2010). [from OMIM]