dic(9; 20): A new recurrent chromosome abnormality in adult acute lymphoblastic leukemia

Abstract

Loss of chromosome 20 and rearrangement of the short arm of chromosome 9 were identified by banding analysis of three adult patients with acute lymphoblastic leukemia (ALL). The G‐banding pattern suggested and identical deletion of 9p, but, also, an unbalanced translocation with chromosome 20 was taken into consideration. Dual‐color chromosome painting with probes for chromosomes 9 and 20 revealed the presence of material from chromosome 20 at the short arm of the abnormal chromosome 9 in all three cases. Centromeric alpha‐satellite DNA of both chromosome 9 and chromosome 20 was demonstrated by fluorescence in situ hybridization and indicated the presence of a dicentric chromosome. The hybridization of a YAC clone of the short arm of chromosome 20 proved that the dicentric chromosome contained the short arm of chromosome 20, which had been suspected from the G‐banding pattern. Thus, the rearrangement was interpreted as dic(9; 20)(pl I;qi I . ? I). Because this was the sole chromosome abnormality in two patients, dic(9; 20) may be a primary chromosome aberration in ALL. In one case, a 9q⁺ chromosome derived from a Philadelphia (Ph) translocation was involved in the formation of the dicentric chromosome. Immunophenotyping revealed CD 1o⁺ B‐cell precursor ALL in all three cases. Whereas the two patients in whom dic(9; 20) was the sole cytogenetically detectable change are in continuous complete remission for 10 and 45 months, respectively, the Ph⁺ patient relapsed with leukemia and died 8 months after diagnosis.