N-RAS MUTATION AND KARYOTYPIC EVOLUTION ARE CLOSELY ASSOCIATED WITH LEUKEMIC TRANSFORMATION IN MYELODYSPLASTIC SYNDROME

We performed a longitudinal analysis of the karyotypes and N-ras gene configuration of bone marrow cells in 35 patients with myelodysplastic syndrome (MDS). Karyotypic evolution was found in eight patients, and was associated with disease progression, including leukemic transform ation, in all the patients. We identified N-ras mutations in six patie nts, using a polymerase chain reaction (PCR) technique, in which oligo nucleotide primers were constructed with induced mismatches, followed by endonuclease digestion. Direct sequencing confirmed single base sub stitutions at codon 12 in two patients and at codon 13 in four. The in cidence of N-ras gene mutations was significantly higher in the karyot ypically evolved group (five of eight patients) than in the stable gro up (one of 27 patients). All of five patients harboring both karyotypi c evolution and an N-ras mutation showed concomitant disease progressi on to overt leukemia or refractory anemia with excess of blasts in tra nsformation (RAEB-T). Two of four patients with either karyotypic evol ution or N-ras mutation and six of 26 patients without any of these al terations also progressed to overt leukemia. Our results indicate that the accumulation of these genetic alterations is closely associated w ith leukemic transformation of MDS, although other genetic alterations may also play a key role in the remaining patients.