Deletion of part of the long arm of chromosome 5 (5q-) is one of the most common structural aberrations in patients with myeloid disorders. The deletion is interstitial and the deleted segment is variable in size and breakpoint localization. Precise analysis of chromosomal breakpoints proved that band 5q31 is the most common deleted region. Extensive molecular studies have been performed to identify one or several tumor suppressor gene(s) in this critical region. Although these genes have not been identified as yet, the candidate genes are being intensively studied. Isolation and characterization of tumor suppressor genes will lead to the understanding of molecular mechanisms of normal hematopoiesis and that of leukemic transformation.

        Key words: deletion 5q, tumor suppressor genes, fluorescence in situ hybridization.