Juvenile Myelomonocytic Leukemia

This condition usually occurs in children less than 5 years old and encompasses conditions previously termed "juvenile chronic myeloid leukemia," infantile monosomy 7 syndrome, and other myelodysplas-tic/myeloproliferative diseases of childhood.

Juvenile myelomonocytic leukemia is particularly associated with monosomy 7.76 In approximately 25-33%, other cytogenetic abnormalities (+8 and abnormalities of chromosome 7) also occur. Furthermore, there is an increased incidence in Down's syndrome and neurofibromatosis. Some 15% of children with JMML have features of neurofibromatosis, these and others without these features have abnormalities of the NF 1 gene. Mutations of the RAS oncogene are present in 15-30%, but these patients do not, to date, have NF 1 abnormalities.77 A further factor of genetic interest includes an occasional tendency for familial cases and increased expression of hemoglobin F.

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