Molecular analysis of chromosome 7q alterations in myeloid disorders

Part or all of chromosome 7 is commonly deleted from bone marrow clones during the development of myeloid disorders, particularly myelodysplasia and acute myeloid leukaemia and is associated with a very poor prognosis. It is proposed that a tumour suppressor gene (or genes) resides on the long arm of this chromosome. Molecular studies have demonstrated loss of heterozygosity for regions between 7q22 and 7q35, with breakpoints at 7q22 and 7q32-34. As part of the human genome mapping project, numerous locus-specific probes are now available and have been useful in defining these critical breakpoint regions further. Although a number of candidate genes are present in the regions of interest, none has so far been analysed critically for the presence of mutations. Experimental data presented here defines the 7q22 and 7q34 breakpoint regions more precisely. Two candidate genes have been identified; the asparagine synthetase (ASNS) gene at 7q22 and the NEDD2 gene at 7q34. ASNS has been studied in detail at the molecular level for the presence of mutations. The association between fragile sites, areas of expansion of trinucleotide repeats, and cancer-related genes may be applicable to chromosome 7 band q32 and provides a good explanation as to why chromosomes break in the first place. If a tumour suppressor gene were found for this group of disorders, an essential step in further analysis is to attempt to reintroduce the lost gene to restore function. For this and to try new therapies, animal models are a necessary resource. No myelodysplasia model exists, thus data is presented here on work carried out to try to establish a model in the immunodeficient mouse. It is hoped that the new information obtained through mapping and animal modelling will improve understanding of the chromosome 7-related myeloid disorders.