Chromosome 20 deletions in myeloid malignancies: reduction of the common deleted region, generation of a PAC/BAC contig and identification of candidate genes. UK Cancer Cytogenetics Group (UKCCG).

Deletion of the long arm of chromosome 20 represents the most common chromosomal abnormality associated with the myeloproliferative disorders (MPDs) and is also found in other myeloid malignancies including myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML). Previous studies have identified a common deleted region (CDR) spanning approximately 8 Mb. We have now used G-banding, FISH or microsatellite PCR to analyse 113 patients with a 20q deletion associated with a myeloid malignancy. Our results define a new MPD CDR of 2.7 Mb, an MDS/AML CDR of 2.6 Mb and a combined 'myeloid' CDR of 1.7 Mb. We have also constructed the most detailed physical map of this region to date--a bacterial clone map spanning 5 Mb of the chromosome which contains 456 bacterial clones and 202 DNA markers. Fifty-one expressed sequences were localized within this contig of which 37 lie within the MPD CDR and 20 within the MDS/AML CDR. Of the 16 expressed sequences (six genes and 10 unique ESTs) within the 'myeloid' CDR, five were expressed in both normal bone marrow and purified CD34 positive cells. These data identify a set of genes which are both positional and expression candidates for the target gene(s) on 20q.

Identification of multiple copies of a 20q-chromosome in a case of myelodysplastic syndrome: a FISH study.

In myelodysplastic syndromes (MDS) karyotypic aberrations identify subgroups of patients with distinct clinical-morphological features and can be relevant in risk assessment of developing leukemia. Often conventional cytogenetic analysis is not sufficiently informative due to the presence of partially or completely unrecognizable chromosome markers. By chromosome microdissection (MD) and fluorescence in situ hybridization (FISH) we investigated the nature of a karyotypic marker occurring in multiple copies in one case of MDS arisen in a patient previously treated for breast cancer. Results showed dicentrics derived from telomeric fusion between interstitially deleted 20q-chromosomes. The abnormal karyotype resulted into polysomy for a deleted chromosome 20q.