CHROMOSOMAL DELETIONS IN THE MYELODYSPLASTIC SYNDROME

Karyotypic abnormalities in primary myelodysplastic syndrome (P-MDS) are less frequent than in secondary myelodysplasia. A review of the literature involving over 3000 reported cases, shows the incidence of karyotypically abnormal clones at presentation in nearly 48% of cases. Approximately 50% of the abnormalities comprise of deletions of chromosomes 5, 7, 11, 12, 13 and 20. Localisation of a number of haemopoietic growth factors and their receptors to the deleted segments of the chromosomes, has invoked considerable interest in the molecular pathology of the interstitial deletions and their consequent role in the multistep pathogenesis of MDS. Present evidence suggests chromosome abnormalities are a later event in the multistep pathogenesis, and it is suggested their occurrence may be restricted to a restricted myeloid progenitor cell, although the initial event(s) occur at the common lymphoid-myeloid progenitor. Much has been gleaned from the dominant modes of leukaemogenesis, such as the occurrence of missense mutations at specific positions of RAS and FMS mutations. It is suggested that a similar enquiry into the mechanisms of chromosomal deletions in P-MDS is required in order to delineate the role of these abnormalities in the clonal evolution of this group of diseases.