DELETIONS OF CHROMOSOME-21 RESTRICTED TO THE LEUKEMIC-CELLS OF CHILDREN WITH DOWN-SYNDROME AND LEUKEMIA

Down syndrome (DS) is associated with an increased risk of developing hematological malignancies, but the basis for this predisposition is s o far unknown. Using fluorescence in situ hybridization with a panel o f locus-specific probes on normal and leukemic metaphases, we have fou nd long-arm interstitial deletions of one of the chromosome 21s in the leukemic cells from five patients with DS and leukemia. This finding provides strong evidence for a gene or genes present on chromosome 21 having an important function in the development of leukemia in individ uals with Down syndrome.