Evaluation of chromosome 5 aberrations in complex karyotypes of patients with myeloid disorders reveals their contribution to dicentric and tricentric chromosomes, resulting in the loss of critical 5q regions.

Dicentric chromosomes have often been observed in complex karyotypes in previously reported studies of therapy-related myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Fluorescence in situ hybridization (FISH) has now made the characterization of these rearrangements much easier. Dicentric and tricentric chromosomes were identified in 21 patients (9 MDS and 12 AML) among the 133 consecutive MDS/AML patients (17%) who had a structural or numerical aberration of chromosome 5 using conventional cytogenetic analysis. One third (7/21) of the patients had received alkylating drugs for a previously diagnosed cancer or chronic myeloproliferative disease. Loss of 5q material was identified in all 21 patients. One copy of the EGR1 (5q31) or the CSF1R (5q33 approximately q34) genes was lost in 20 of the 21 patients. Dicentric and tricentric chromosomes involving chromosome 5 are frequently observed in complex karyotypes among patients with de novo or therapy-related MDS/AML. They lead to deletions of various parts of the long arm of chromosome 5.