Demonstration of acquired hemizygosity and clonality in acute lymphoblastic leukemia with chromosome 7 abnormalities using hypervariable DNA probes

Clonal abnormalities of chromosome(s) 7 were investigated in two patients with acute lymphoblastic leukemia. The abnormal karyotypes were 46,XY,–7,del(6)(q13q21),+i(7q)/47,XY,del(6),+i(7q) in case 1, and 46,XX,–7,t(4;11)(q21;q23),+i(7q) in case 2. DNA from leukemic tissue was investigated with Southern blotting using hypervariable DNA probes λMS31 and pλg3 located on 7p and 7q, respectively. Restriction fragment length polymorphisms (RFLPs) were detected on the short arm in case 1 and on both arms in case 2, and a marked difference in intensity between the two alleles was observed. In case 1 the acquired hemizygosity of 7p, suggested by the cytogenetic findings, was confirmed by Southern blotting. Thus, one chromosome 7 formed the i(7q) and the other No. 7 was duplicated. In case 2 the results of the Southern blotting indicated that the size of the clone with i(7q) was considerably greater than suggested by cytogenetic analysis of the few available metaphase cells.