Fluorescence in situ hybridization for the study of cell lineage involvement in myelodysplastic syndromes with chromosome 5 anomalies

Fluorescence in situ hybridization (FISH) with a locus-specific dual DNA probe (LSI EGR-1SO/D5S23SG) for chromosome 5 was used in combination with morphology to study bone marrow cell lineage involvement of the abnormal chromosomal clone in 13 patients with deletion 5q [del(5q)], either as a sole aberration or as part of a complex karyotype, and in six cases with monosomy 5 by metaphase cytogenetics, all with complex karyotypes including 2–6 marker chromosomes. In the monosomy 5 group, only one case displayed the expected one orange and one green (1O + 1G) FISH pattern in a majority of the cells. The other five patients instead showed 1O + 2G FISH signals in 17–86% of the bone marrow cells, which is the typical pattern for del(5q). In the del(5q) group, 26–98% of the bone marrow cells exhibited 1O + 2G FISH signals. All patients showed clonal involvement of the myeloid cell lineages, including the megakaryocytes in a few cases, whereas lymphoid cells generally exhibited the normal 2O + 2G FISH pattern. No difference was seen between patients with 5q− syndrome, those with del(5q) and a complex karyotype, and the monosomy 5 group. We were thus unable to confirm the recent suggestion that B-cells are a part of the abnormal clone in MDS with del(5q). Furthermore, true monosomy 5 seems to be rare in MDS.