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 lambda MS31 and p lambda g3 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.