Tiling resolution array CGH of dic(7;9)(p11 similar to 13;p11 similar to 13) in B-cell precursor acute lymphoblastic leukemia reveals clustered breakpoints at 7p11.2 similar to 12.1 and 9p13.1

The dic( 7; 9)( p11 similar to 13; p11 similar to 13) is a recurrent chromosomal abnormality in acute lymphoblastic leukemia (ALL), mainly of B-lineage. Although more than 20 dic(7; 9)-positive ALLs have been reported to date, the molecular genetic consequences of this aberration are unknown. We performed tiling resolution (32K) genome-wide array-based comparative genomic hybridization ( array CGH) analysis of three cases with dic(7; 9) in order to characterize the breakpoints on 7p and 9p. The analysis showed a clustering of breakpoints within 9p13.1 in all three cases and within 7p11.2 in two cases; the array CGH revealed two different breakpoints - 7p12.1 and 7p14.1 - in the remaining case. Based on these findings the abnormality should hence be designated dic(7; 9)(p11.2 similar to 12.1; p13.1). Locus-specific fluorescence in situ hybridization analysis of one of the cases narrowed down the 7p11.2 breakpoint to a < 500-kb segment in this sub-band, a region containing three known genes. Unfortunately, lack of material precluded further molecular genetic studies, and it thus remains unknown whether the pathogenetically important outcome of the dic(7; 9) is formation of a chimeric gene or loss of 7p and/or 9p material. Copyright (c) 2007 S. Karger AG, Basel.