LOCALIZATION BY CHROMOSOME MICRODISSECTION OF A RECURRENT BREAKPOINT REGION ON CHROMOSOME-6 IN HUMAN B-CELL LYMPHOMA

Deletion of the long arm of chromosome 6 (6q) is one of the most commo n chromosomal alterations in human B-cell lymphomas, Conventional cyto genetic banding analysis and loss-of-heterozygosity (LOH) studies have detected several common regions of deletion ranging across the entire long arm (6q), with no defined recurrent breakpoint yet identified, W e describe here a strategy combining chromosome microdissection and fl uorescence in situ hybridization (Micro-FISH) to determine a minimal r egion of deletion along chromosome 6. Seven clinical cases and one cel l line of follicular lymphoma containing a t(14;18) and one case of di ffuse lymphoma, also with a t(14;18), were used for this study, All ni ne cases had previously defined abnormalities of chromosome 6 determin ed by cytogenetic analysis. The results of chromosome dissection were unexpected and in contrast to the suggestion of disparate breakpoints by conventional chromosome banding. Specifically, Micro-FISH analysis provided evidence for a common breakpoint at 6q11 in seven of nine cas es, After Micro-FISH analysis, all of the presumed simple deletions of chromosome 6 were carefully reanalyzed and shown to actually represen t either nonreciprocal translocations (three cases), interstitial dele tions (five cases), or isochromosome (one case), The recurrent proxima l breakpoint (6q11) was detected in seven of nine cases, with the mini mal region of deletion encompassing 6q11 to 6q21. By analogy to other tumor systems, the identification of recurring breakpoints within 6q11 may suggest that a gene(s) important to the genesis or progression of follicular lymphoma can be localized to this band region.