Acquisition of loss of the wild-type NRAS locus with aggressive disease progression in a patient with juvenile myelomonocytic leukemia and a heterozygous NRAS mutation

In a patient with juvenile myelomonocytic leukemia, a NRAS mutation at codon 12 (GGT>TGT) was initially heterozygous, but became homozygous after blastic crisis (BC). According to microsatellite and FISH analyses, the post-BC homozygous mutation might result from the loss of the wild-type NRAS locus through mitotic recombination.