Cytogenetic and molecular diagnosis of chromosome 5 deletions in myelodysplasia

Deletions of chromosome 5, del(5q), are frequently observed in myelodysplas ia (MDS). We evaluated molecular detection of loss of heterozygosity (LOH) as a diagnostic method to detect del(5q) in a series of 60 MDS cases at a s ingle institution. LOH was compared to cytogenetics on the same clinical sp ecimen, resolving ambiguous cases by fluorescent in situ hybridization (FIS H) and additional LOH. There was poor concordance between molecular and cyt ogenetic results, but most discrepancies could be resolved by FISH and addi tional LOH. Molecular analysis was of low sensitivity because most cases co ntained a relatively high proportion of cells without del(5q), but it was a ccurate, while cytogenetics overestimated the proportion of cells with del( 5q) and failed to detect some cases with complex rearrangements. Minor clon es were detected both by FISH and LOH. Overall, we found an incidence of 23 % (14 of 60 cases) for del(5q) in MDS. The results also suggest that there is a high degree of genetic heterogeneity in the cellular population of MDS . Although del(5q) is common in MDS, it may not be present in all cells, le ading to diagnostic challenges.