RAS mutations and clonality analysis in children with juvenile myelomonocytic leukemia (JMML)

Juvenile myelomonocytic leukemia (JMML) is a malignant hematopoietic disord er of early childhood with excessive proliferation of the myeloid and monoc ytic lineage. Deregulation of the RAS signal transduction pathway is though t to play a key role in its pathogenesis. We examined peripheral blood or b one marrow cells of 36 children with JMML for activating point mutations in codons 12, 13 and 61 of the NRAS and KRAS proto-oncogenes by allele-specif ic restriction assay, single-strand conformation polymorphism and/or direct sequencing. Codons 12, 13 and 61 of HRAS were examined in 26 of these pati ents. We detected RAS mutations in six cases (17%) located at N12 (n = 2), N13 (n = 3) and K13 (n = 1). In addition, we performed clonality studies on different cell lineages in four of these patients applying the RAS mutatio n, the karyotype and X-chromosome inactivation patterns as clonal markers. Erythroid cells carried mutant RAS, indicating clonal origin. In EBV B cell lines, one of three patients studied harbored a RAS mutation, while the ot her two patients had polyclonal B cells with wild-type RAS. T lymphocytes w ere examined in one patient; they were polyclonal and had wild-type RAS. It is likely that JMML is a heterogeneous disease with respect to clonal invo lvement of different lineages.