FISH investigation of 5q and 7q deletions in MDS/AML reveals hidden translocations, insertions and fragmentations of the same chromosomes.

We have studied, by fluorescence in situ hydridization (FISH), chromosomes 5 and 7 in a series of 11 cases with 5q deletion, as sole anomaly (four cases), or in association with 7q deletion (seven cases), in MDS/AML patients. We found that, in some cases, a part of the so-called 'lost' chromosome 5 and 7 material, was actually translocated. These translocations may be either end-arm or whole-arm, as well as small insertions. Chromosomes 5 or 7 may be broken in more than two segments, defining 'fragmentation', giving rise to marker chromosomes. FISH allowed the identification of small material insertion, which is totally unidentified by classical cytogenetics. Chromosome 5 and 7 translocations occur irrespectively of the 'de novo' or 'secondary' type of myelodysplastic syndrome (MDS)/acute myeloid leukaemia (AML) patients.