DETECTION OF NUMERICAL CHROMOSOME-ABNORMALITIES BY FISH IN CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA

Fluorescence in situ hybridization (FISH) was performed on interphase bone marrow cells to study numerical chromosome abnormalities in child hood acute lymphoblastic leukemia (ALL). Ten patients were selected fo r this study on the basis of having an extra chromosome 6 in the abnor mal clone of the bone marrow at diagnosis. The numerical changes that were detected by FISH with a chromosome 6 specific alpha-satellite DNA probe correlated well with the cytogenetic and clinical data in all p atients. Three hybridization signals were seen in 43.8-83.0% of interp hase cells in the specimens with a hyperdiploid karyotype. The diagnos tic bone marrow sample of the patient with a tetraploid karyotype reve aled four signals in 67.0% of cells. Two signals were detected in the majority of the cells in the three nonleukemic control bone marrow sam ples (97.0-97.7%), assessing the cut-off Value of about 1 % for trisom y 6. This study demonstrates that FISH analysis is a useful and sensit ive fool to screen for the presence of extra chromosomes in interphase cells and is important clinically for evaluating the achievement and maintenance of remission in hyperdiploid childhood ALL. However, to de tect structural chromosome aberrations which carry important diagnosti c and prognostic information, as seen in our patient with the transloc ation t(1;19) at diagnosis but not at relapse, conventional cytogeneti c analysis should be performed both at diagnosis and at relapse.